climate zone essay

What Are the Major Climate Zones?

Climate zones dictate the weather and plant life native to a region.

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The Discovery of Earth’s Climate Zones

The main climate zones, regional climate zones.

• Do Earth's Climate Zones Shift?

Earth's climate zones—the horizontal belts of different climates that encircle the planet—consist of tropical, dry, temperate, continental, and polar zones.  

These major climate zones exist thanks to Earth’s diverse landscapes. Each country is located at a specific latitude and elevation, next to either a particular landmass, body of water, or both. As a result, they are impacted differently by certain ocean currents or winds. Likewise, a location’s temperatures and precipitation patterns are influenced in a unique way. And it’s this unique mix of influences that yields different climate types.

As abstract as climate zones may seem, they remain a key tool for understanding earth’s many biomes , tracking the extent of climate change, determining plant hardiness , and more.

The concept of climate zones dates back to ancient Greece. In the 6th century B.C., a pupil of Pythagoras was the first to suggest the idea.

A few centuries later, the famous Greek scholar Aristotle hypothesized that the earth’s five circles of latitude (the Arctic Circle, Tropic of Capricorn, Tropic of Cancer, Equator, and Antarctic Circle) divided the Northern and Southern hemispheres into a torrid, temperate, and frigid zone. However, it was Russian-German scientist Wladimir Köppen who, in the early 1900s, created the climate classification scheme we use today.

Because little climate data existed at that time, Köppen, who also studied botany, began observing the relationship between plants and climate. If a species of plant needed special temperatures and rainfall to grow, he thought, then a location’s climate could be inferred simply by observing the plant life native to that area.

Maulucioni / Wikimedia Commons / Public Domain

Using his botanical hypothesis, Köppen determined that five major climates exist worldwide: tropical, dry, temperate, continental, and polar.

Tropical (A)

Tropical climate zones lie near the Equator and have continually high temperatures and high precipitation. All months have average temperatures above 64 degrees F (18 degrees C), and 59 plus inches (1,499 mm) of annual rainfall is normal.

Dry or arid climate zones experience high temperatures year-round, but little annual precipitation. 

Temperate (C)

Temperate climates exist in Earth’s middle latitudes and are influenced by both the land and water that surrounds them. In these zones, wider temperature ranges are experienced throughout the year, and seasonal variations are more distinct.

Continental (D)

Continental climates also exist in the mid-latitudes, but as the name implies, they’re generally found at the interiors of large landmasses. These zones are characterized by temperatures that swing from cold in winter to warm in summer, and moderate precipitation that occurs mostly in the warmer months or as snowstorms in the colder months.

Polar climate zones are too harsh to support vegetation. Both winters and summers are very cold, and the warmest month has an average temperature below 50 degrees F (10 degrees C).

In later years, scientists added a sixth major climate zone—the highland climate. It includes the variable climates found in the world’s high mountain regions and plateaus.

What's With All the Letters?

As seen on Köppen-Geiger climate maps, each climate zone is abbreviated by a string of two or three letters. The first letter (always capitalized) describes the main climate group. The second letter indicates precipitation patterns (wet or dry). And if there’s a third letter present, it describes the climate’s temperatures (hot or cold).

Köppen’s five climate groups do a good job of telling us where the world’s hottest, coldest, and in-between climates are, but they don’t capture how local geographical features, such as mountains or lakes, influence seasonal precipitation and temperatures. Realizing this, Köppen split his main categories into subcategories called regional climates .

Some of the above climate subzones can be further classified by temperature. For example, deserts can be either "hot" or "cold" depending on whether their average annual temperature is above 64 degrees F (18 degrees C) or below it. When you consider the five major climate zones, plus this cornucopia of subzones, a total of more than 30 unique regional climate zones exist.

Do Earth's Climate Zones Shift?

As temperature and precipitation patterns across a region change, the region’s climate zone, which is based on those parameters, will also change. Between 1950 and 2010, human-caused climate change shifted nearly six percent of the global land area toward warmer and drier climate types, according to a 2015 study in Scientific Reports .  

Mahmud, Khandakar Hasan, et al. " Development of Climate Classification Map for Bangladesh Based on Koppen's Climate Classification ." The Jahangirnagar Review , vol. 39, 2015, pp. 23-36.

" Climate Zones ." National Oceanic and Atmospheric Administration .

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Chan, Duo and Qigang Wu. " Significant Anthropogenic-Induced Changes of Climate Classes Since 1950 ." Scientific Reports , vol. 5, 2015, 13487, doi:10.1038/srep13487

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A young boy herds his goats in the Ghat District of Libya, which has been converted largely to desert in the last 100 years. TAHA JAWASHI/AFP/Getty Images

Redrawing the Map: How the World’s Climate Zones Are Shifting

Rising global temperatures are altering climatic zones around the planet, with consequences for food and water security, local economies, and public health. Here’s a stark look at some of the distinct features that are already on the move.

By Nicola Jones • October 23, 2018

As human-caused emissions change the planet’s atmosphere, and people reshape the landscape, things are changing fast. The receding line of Arctic ice has made headlines for years, as the white patch at the top of our planet shrinks dramatically. The ocean is rising, gobbling up coastlines. Plants, animals, and diseases are on the move as their patches of suitable climate move too.

Sometimes, the lines on the map can literally be redrawn: the line of where wheat will grow, or where tornadoes tend to form, where deserts end, where the frozen ground thaws, and even where the boundaries of the tropics lie.

Here we summarize some of the littler-known features that have shifted in the face of climate change and pulled the map out from under the people living on the edges. Everything about global warming is changing how people grow their food, access their drinking water, and live in places that are increasingly being flooded, dried out, or blasted with heat waves. Seeing these changes literally drawn on a map helps to hammer these impacts home.

The tropics are getting bigger at 30 miles per decade

The tropics are expanding by half a degree per decade. Source: Staten et al., Nature Climate Change, 2018. Graphic by Katie Peek.

On an atlas, the boundary of the tropics is marked out by the Tropic of Cancer and the Tropic of Capricorn, at about 23 degrees north and south. These lines are determined by where the sun lies directly overhead on the December and June solstices. But from a climate perspective, most scientists draw the edges of the tropics instead at the nearby boundary of the Hadley cell — a large-scale circulation pattern where hot air rises at the equator, and falls back to earth, cooler and drier, somewhere around 30 degrees latitude north (the top of the Sahara desert and Mexico) and 30 degrees south (the bottom of the Kalahari Desert).

The word “tropical” often brings to mind rainforests, colorful birds, and lush, dripping foliage, but the vast majority of our planet’s middle region is actually quite dry. “The ratio is something like 100 to 1,” says Jian Lu, a climate scientist at the Pacific Northwest National Laboratory in Richland, Washington. About a decade ago, scientists first noticed that this dry belt seemed to be getting bigger. The dry edges of the tropics are expanding as the subtropics push both north and south, bringing ever-drier weather to places including the Mediterranean. Meanwhile, the smaller equatorial region with heavy rains is actually contracting, Lu says: “People call it the tropic squeeze .”

In a paper published in August, Lu and colleagues tracked how and why the Hadley cell is expanding. They found that since satellite records started in the late 1970s, the edges of the tropics have been moving at about 0.2-0.3 degrees of latitude per decade (in both the north and the south) .The change is already dramatic in some areas, Lu says — the average over 30 years is about a degree of latitude, or approximately 70 miles, but in some spots the dry expansion is larger. The result is that the boundary between where it’s getting wetter and where it’s getting drier is pushing farther north , making even countries as far north as Germany and Britain drier. Meanwhile, already dry Mediterranean countries are really feeling the change: In 2016, for example, the eastern Mediterranean region had its worst drought in 900 years . The last time the tropics expanded northward (from 1568 to 1634 , due to natural climate fluctuations), droughts helped to trigger the collapse of the Ottoman Empire.

There are several reasons for the shift in the Hadley cell, Lu’s team reports, including the ozone hole in the Southern Hemisphere and warming black soot in air pollution from Asia, along with rising air temperatures from greenhouse gases. Changes in sea surface temperatures, Lu says, seems to be causing at least half of the shift. That means predicting future tropical expansion is difficult, says Lu. “We can’t put a number on it, but we have a rough idea it will keep increasing.”

The Sahara desert has gotten 10 percent bigger since 1920

Since 1902, the Sahara Desert has grown 10 percent, advancing as much as 500 miles northward over the winter months in some spots. Source: Thomas & Nigam, Journal of Climate, 2018. Graphic by Katie Peek.

The world’s largest warm-weather desert is getting bigger. The Sahara already covers a vast 3.6 million square miles — an area nearly as large as the United States. The desert’s edges are defined by rainfall; the line is usually drawn where the ground sees just 4 inches per year. When Natalie Thomas and Sumant Nigam, ocean and atmospheric scientists at the University of Maryland, looked at records stretching from 2013 back to 1920, they found that these boundaries for the Sahara had crept both northward and southward, making the entire region about 10 percent larger.

The change, which is expected to reduce some countries’ ability to grow food, hardly seems fair. “Morally, how do we deal with the fact that developing countries are paying the price?” says Thomas. One study in the 1990s showed that the limit of where plants could grow in the dry southern edge of the Sahara had moved nearly 81 miles south in the 10 years between 1980 and 1990.

Across most of the Sahara the change is on the order of tens of miles over the study period, but in other spots it’s far more dramatic: Libya has gone from being mostly not desert in 1920, to mostly desert in 2013, as the line there has advanced a shocking 500 miles or so in winter months. Lake Chad, which sits on the southern edge of the Sahara, shrank dramatically from 9,600 square miles in the 1970s to less than 770 square miles in the 1990s, in part due to reduced rainfall in the Sahel, the dry region just to the south of the Sahara.

Nigam and his colleague calculate that about two-thirds of the change might be accounted for by natural climate cycles, such as the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation, which help to determine rainfall. But the remaining third, they reckon, is down to climate change — the northern edge of the desert, for example, seems to be moving because of the climate-driven poleward creep of the tropics.

The 100th Meridian has shifted 140 miles east

The arid Western plains of North America meet the wetter, eastern region near the 100th Meridian. This climatic boundary has shifted about 140 miles east since 1980. Source: Seager et al., Earth Interactions, 2018. Graphic by Katie Peek.

Back in the 1870s, scientist and explorer John Wesley Powell noticed a stark transition between the arid Western plains of North America and the wetter, eastern region. As he wrote, “passing from east to west across this belt a wonderful transformation is observed”: a “luxuriant growth of grass” gives way to “naked” ground with the occasional cacti. The line between the two regions goes from Mexico to Manitoba, cutting right through the continent’s breadbasket. To the east, farmers grow mainly rain-loving corn; to the west, mainly drought-resistant wheat.

This climatic transition has long been called the 100th Meridian, after the longitudinal line that it roughly matches up with. But in March, climate scientist Richard Seager of the Lamont–Doherty Earth Observatory of Columbia University and colleagues published papers showing the transition is on the move .

The reasons for the existence of the line are many: the Rocky Mountains force the wet air blowing in from the Pacific to rain out before the winds reach the plains; Atlantic storms and winds from the Gulf of Mexico bring moisture to the east. Now things are changing. Rainfall hasn’t changed much in the northern plains, but rising temperatures are increasing evaporation from the soil and drying things out. Meanwhile, rainfall is diminishing further south due to shifts in wind patterns. In total, that seems to have moved the line about 140 miles eastward since 1980, Seager calculated. The shift seen so far might be due to natural variability, he says, but it’s in line with what we expect to keep happening because of climate change. And it will keep moving east as the planet keeps warming.

U.S. farmers don’t seem to report problems or changes yet, Seager says, but he predicts that the country’s agriculture will eventually have to adapt, by adding more irrigation, for example, using different seeds, or shifting their crop entirely from one plant to another.

Tornado Alley has shifted 500 miles east in 30 years

Hotspots for tornado formation in the U.S. have shifted east 500 miles since the mid-1980s, along with shifts in temperatures. Source: Agee et al, Journal of Applied Meteorology and Climatology, 2016. Graphic by Katie Peek.

The author of the Wizard of Oz likely chose Kansas for the book’s setting for a reason: it was smack dab in the middle of “Tornado Alley,” the stretch from South Dakota to Texas that’s infamous for destructive storms. But things are changing; research shows that tornados are now more likely to hit homes some 500 miles to the east in Southern states, including Tennessee and Alabama.

Earth scientist Ernest Agee of Purdue University in Indiana and colleagues looked at tornado activity going back to the 1950s when modern tornado records began, and compared the first 30 years of records to the next 30. This showed a clear shift in where tornadoes were hitting hardest, both in terms of the total number of tornadoes and the number of tornado days. In the first half of the study period, from 1954 to 1983, an area in Oklahoma was king, with a total of 477 tornadoes. But that area’s tornado count decreased dramatically, by 45 percent, in the second half of the study period, from 1984 to 2013. Meanwhile, an equivalently sized area in northern Alabama bumped up 48 percent to 477 large tornadoes. Tennessee’s number of days of violent tornadoes doubled, from 14 to 28 days, making the state arguably the new heart of tornado activity, the authors argue.

The researchers don’t know exactly why the shift happened. Part of the reason might be attributed to who is reporting tornados, notes co-author Sam Childs, an atmospheric scientist at Colorado State University. “The storm prediction center is based out of Oklahoma City. There were a lot of reports there at first, and that’s broadening out with time,” Childs says. “But there’s definitely a meteorological effect too.” The shift in tornadoes matches up with a change in the weather, he notes. The eastern half of the U.S. was about 1.2 degrees Fahrenheit warmer during the second half of the study, making it likely that climate had something to do with the move.

The general link between weather and tornadoes is fairly well established. Tornadoes need several things to form, including warm, wet, buoyant air and high wind shear. As the 100 th Meridian moves eastward, it is pushing drier conditions further east (Oklahoma lies right on that line). But it’s hard to say why Tennessee is seeing more of them, and the future for tornado activity is hard to predict.

Plant Hardiness Zones are moving north in the U.S. at 13 miles per decade

Hardiness zones in the U.S., which track average low temperatures in winter, have all shifted northward by half a zone warmer since 1990. Source: United States Department of Agriculture. Graphic by Katie Peek.

As any gardener knows, the easiest way to keep track of which plants will fare well where you live, or when to plant your tomatoes to avoid a spring frost, is by taking note of your “ hardiness zone .” In the frozen depths of Alaska and Siberia’s zone 1, you might want to plant something like Yarrow to survive overwinter; in zone 5, which cuts through the Corn Belt in the U.S. Midwest, you can plant asparagus in March or April.

Hardiness maps are published around the world, but it’s easiest to see change where the idea was first developed, in the United States. The U.S. Department of Agriculture’s hardiness map, first published in 1960, is based on the average annual minimum temperature of any given spot — a metric that plays a big part in determining if perennial crops like orange trees will make it through the coldest months. Each zone marks out a 10 degrees F band, from -60 to -50 degrees F in zone 1 to 60 to 70 degrees F in zone 13. When that map was last updated , in 2012, nearly half the country was upgraded to half a zone warmer than it had been in 1990; in other words, all the lines shifted on average a little to the north. That was partly thanks to more detailed mapping techniques, the authors of the map reported, but also because temperatures were warmer in the more recent data set.

The researchers who produced the 2012 revision stopped short of saying the change was due to climate change, especially since the method of how they produced the map changed so much from one version to the next. But others have followed up on the same idea to show how climate change, specifically, is shifting U.S. hardiness zones.

Lauren Parker and John Abatzoglou of the University of Idaho tracked what would happen to hardiness zones from 2041 to 2070 under future global warming scenarios, and found the lines will continue to march northward at a “climate velocity” of 13.3 miles per decade. That means big changes in store for three major cash crops, they note. Almonds will see their suitable growing range expand from 73 percent of the continental U.S. from 1971-2000 to 93 percent from 2041–2070. Kiwifruit will bump up from 23 percent to 32 percent during the same period, and oranges from 5 percent to 8 percent.

So the shift in hardiness zones is good news for perennial cash crops in the U.S., but not necessarily good news overall for food security in North America, or globally. “On the plus side, if we can expand the range over which we grow crops, that’s a good thing,” says Parker. But, she adds, “On the flip side, you also allow for the expansion of weeds and pests.”

The permafrost line has moved 80 miles north in 50 years in parts of Canada

As global air temperatures rise, permafrost is retreating north, moving as far as 80 miles poleward over a half-century in parts of Canada. Source: Berkeley Earth. Graphic by Katie Peek.

As the planet warms, the Arctic is feeling it the most: Temperatures in northern regions are rising at about twice the global average. That’s having a huge impact on the region’s permafrost, ground that typically stays frozen all year round. As the line delineating an average temperature of 0 degrees Celsius moves north, so too does the permafrost line. “They roughly track together,” says Kevin Schafer, a permafrost expert at the U.S. National Snow and Ice Data Center.

Permafrost isn’t particularly well documented: It’s underground, so out of sight of satellites, and the Arctic is only sparsely covered with meteorological stations. “There aren’t a lot of measurements that far north,” says Schafer. That means much of the evidence of permafrost thaw so far is either anecdotal or limited to specific well-monitored regions. One study in northern Canada found that the permafrost around James Bay had retreated 80 miles north over 50 years. Studies of ground temperatures in boreholes have also revealed frightening rates of change, says Schafer. “What we’re seeing is 20 meters down, it’s increasing as high as 1-2 degrees C per decade,” he says. “In the permafrost world that’s a really rapid change. Extremely rapid.”

The future looks similarly dire. One study predicts that by 2100, the area covered by permafrost might shrink from nearly 4 million square miles to less than 0.4 million ; most of Alaska and the southern tip of Greenland would be permafrost-free.

The impacts are expected to be huge on both a local and global level. Right now, permafrost acts like cement, keeping the ground firm and impermeable to water. As it thaws, buildings and infrastructure collapse. In the northern Russian city of Norilsk , buildings are already tilting, cracking, and becoming condemned. In Bethel , Alaska, roads are buckling and homes collapsing. Many of the Arctic’s uncountable small lakes will also drain away. “That’s going to have a massive impact on the [region’s] ecology,” says Schafer. Meanwhile, the thaw will also release vast amounts of climate-warming methane into the atmosphere.

The Wheat Belt is pushing poleward at up to 160 miles per decade

Between 1990 and 2015, production dropped in much of Australia's Wheat Belt due to drier than average conditions. The areas that disappear from this map are those where output dropped 50 percent or more. Source: Hochman, Gobbett, & Horan, Global Change Biology, 2017. Graphic by Katie Peek.

Australia, renowned for its interior deserts and coastal beaches, is also one of the planet’s largest wheat exporters — just after Canada, Russia, and the U.S. But the arable land at the nation’s southern edge is shrinking, and its potential for growing wheat declining.

In the 1860s, surveyor George Goyder drew a line to show where the edge of Australia’s arable land ended. More than a century later, Goyder’s line is still considered an important feature in determining the country’s “cropping belt.” But climate change is making that land drier, effectively pushing the line further south .

Any given patch of land has a “theoretical potential” for the amount of wheat it can support, given its soil, the climate, and other factors. Reductions in rainfall and warmer temperatures have already reduced the theoretical potential of southern Australia by 27 percent since 1990 . So far, farmers have managed to adapt to the changing conditions and squeeze the same amount of wheat out of their lands. By tweaking things such as their seeds and harvesting practices, they have gone from harvesting 38 percent of their theoretical maximum in 1990 to 55 percent in 2015. But that can only go on so long — farmers can typically only reach about 80 percent of any given parcel of land’s maximum potential. Once they hit that limit, Australian farmers probably won’t be able to counteract the effects of the changing climate any longer. Zvi Hochman, of Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO), says he expects to see actual yields start to drop around 2040. Places like the farming community of Orroroo, currently right on top of Goyder’s line, will be “ significantly impacted ,” writes Julia Piantadosi of the University of South Australia in Adelaide — they won’t be able to keep farming the way they are doing today.

North America is seeing the opposite phenomenon: Its arable land is romping northward, expanding the wheat belt into higher and higher latitudes. Scientists project it could go from about 55 degrees north today to as much as 65 degrees North — the latitude of Fairbanks, Alaska — by 2050. That’s about 160 miles per decade. That’s not all good news, as the southern edge gets drier, hotter, and less agriculturally productive. One study showed that U.S. farmers will likely have to change the strains of wheat they grow, while France and Turkey will have to invest heavily in irrigation systems. In Asia, half of the Indo-Gangetic Plains, which account for 15 percent of global wheat production, are predicted to become heat-stressed by 2050 , significantly cutting yields.

Correction, October 23, 2018: An earlier version of this article incorrectly stated that one degree of latitude equals 100 miles. It is actually nearly 70 miles on average.

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Climate Systems and Change

Climate zones and biomes.

A climate zone results from the climate conditions of an area: its temperature, humidity, amount and type of precipitation, and the season. A climate zone is reflected in a region’s natural vegetation. Perceptive travelers can figure out which climate zone they are in by looking at the vegetation, even if the weather is unusual for the climate on that day.

The major factors that influence climate determine the different climate zones. In general, the same type of climate zone will be found at similar latitudes and in similar positions on nearly all continents, both in the Northern and Southern Hemispheres. The one exception to this pattern is the climate zones called the continental climates, which are not found at higher latitudes in the Southern Hemisphere. This is because the Southern Hemisphere land masses are not wide enough to produce a continental climate.

The most common system used to classify climatic zones is the Köppen classification system . This system is based on the temperature , the amount of precipitation , and the times of year when precipitation occurs. Since climate determines the type of vegetation that grows in an area, vegetation is used as an indicator of climate type.

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A climate type and its plants and animals make up a biome . The organisms of a biome share certain characteristics around the world, because their environment has similar advantages and challenges. The organisms have adapted to that environment in similar ways over time. For example, different species of cactus live on different continents, but they have adapted to the harsh desert in similar ways.

The Köppen classification system recognizes five major climate groups, each with a distinct capital letter A through E. Each lettered group is divided into subcategories. Some of these subcategories are forest (f), monsoon (m), and wet/dry (w) types, based on the amount of precipitation and season when that precipitation occurs .

• Dynamic Earth: Introduction to Physical Geography. Authored by : R. Adam Dastrup. Located at : http://www.opengeography.org/physical-geography.html . Project : Open Geography Education. License : CC BY-SA: Attribution-ShareAlike
• World Koppen Classification (with authors). Authored by : Peel, M. C., Finlayson, B. L., and McMahon, T. A. (University of Melbourne). Enhanced, modified, and vectorized by Ali Zifan. Located at : https://commons.wikimedia.org/wiki/File:World_Koppen_Classification_(with_authors).svg . License : CC BY-SA: Attribution-ShareAlike
• What is climate? - Met Office climate change guide. Authored by : Met Office - Weather. Located at : https://youtu.be/bjwmrg__ZVw . License : All Rights Reserved . License Terms : Standard YouTube License
• How does the climate system work?. Authored by : Met Office - Weather. Located at : https://youtu.be/lrPS2HiYVp8 . License : All Rights Reserved . License Terms : Standard YouTube License
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Earth's Changing Climate

Climate change is a long-term shift in global or regional climate patterns. Often climate change refers specifically to the rise in global temperatures from the mid 20th century to present.

Earth Science, Geography, Human Geography, Physical Geography

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Climate  is the long-term pattern of weather in a particular area. Weather can change from hour to hour, day to day, month to month or even from year to year. For periods of 30 years or more, however, distinct  weather patterns occur. A  desert  might experience a rainy week, but over the long term, the region receives very little rainfall . It has a dry climate .

Because climates are mostly constant, living things can  adapt  to them. Polar bears have adapted to stay warm in  polar climates , while cacti have evolved to hold onto water in  dry climates . The  enormous  variety of life on Earth results in large part from the variety of climates that exist.

Climates do change, however—they just change very slowly, over hundreds or even thousands of years. As climates change, organisms that live in the area must adapt ,  relocate , or risk going  extinct .

Earth’s Changing Climate Earth’s climate has changed many times. For example,  fossils from the Cretaceous period (144 to 65 million years ago) show that Earth was much warmer than it is today.  Fossilized plants and animals that normally live in warm  environments have been found at much higher  latitudes than they could survive at today. For instance,  breadfruit  trees ( Artocarpus altilis ), now found on  tropical   islands , grew as far north as Greenland.

Earth has also experienced several major  ice ages —at least four in the past 500,000 years. During these periods, Earth’s  temperature   decreased , causing an  expansion  of  ice sheets and  glaciers . The most recent Ice Age began about two million years ago and peaked about 20,000 years ago. The ice caps began retreating 18,000 years ago. They have not disappeared completely, however. Their presence in Antarctica and Greenland suggests Earth is still in a sort of ice age. Many scientists believe we are in an  interglacial period , when warmer temperatures have caused the ice caps to  recede . Many centuries from now, the glaciers may advance again. Climatologists look for evidence of past climate change in many different places. Like clumsy criminals, glaciers leave many clues behind them. They scratch and  scour   rocks as they move. They deposit sediment  known as glacial till. This sediment sometimes forms mounds or ridges called  moraines . Glaciers also form elongated oval hills known as  drumlins . All of these geographic features on land that currently has no glaciers suggest that glaciers were once there. Scientists also have chemical evidence of ice ages from sediments and  sedimentary rocks . Some rocks only form from glacial material. Their presence under the ocean or on land also tells scientists that glaciers were once present in these areas. Scientists also have paleontological evidence—fossils. Fossils show what kinds of animals and plants lived in certain areas. During ice ages, organisms that are adapted to cold weather can increase their range , moving closer to the  Equator . Organisms that are adapted to warm weather may lose part of their  habitat , or even go extinct.

Climate changes occur over shorter periods, as well. For example, the so-called  Little Ice Age  lasted only a few hundred years, peaking during the 16th and 17th centuries. During this time, average global temperatures were 1 to 1.5 degrees Celsius (2 to 3 degrees Fahrenheit) cooler than they are today.

A change of one or two degrees might not seem like a lot, but it was enough to cause some pretty massive effects. For instance, glaciers grew larger and sometimes engulfed whole mountain villages. Winters were longer than usual, limiting the growing seasons of  crops . In northern Europe, people deserted farms and villages to avoid  starvation .

One way scientists have learned about the Little Ice Age is by studying the rings of trees that are more than 300 years old. The thickness of  tree rings is related to the amount of the trees’ annual growth. This in turn is related to climate changes. During times of  drought  or cold, trees could not grow as much. The rings would be closer together.

Some climate changes are almost predictable . One example of regular climate change results from the warming of the surface waters of the tropical eastern Pacific Ocean. This warming is called El Niño —The Child—because it tends to begin around Christmas. In normal years,  trade winds blow steadily across the ocean from east to west, dragging warm surface water along in the same direction. This produces a shallow layer of warm water in the eastern Pacific and a buildup of warm water in the west. Every few years, normal winds falter and ocean currents reverse. This is El Niño. Warm water deepens in the eastern Pacific. This, in turn, produces  dramatic  climate changes. Rain decreases in Australia and southern Asia, and freak storms may pound Pacific islands and the west coast of the Americas. Within a year or two, El Niño ends, and climate systems return to normal.

Natural Causes of Climate Change Climate changes happen for a variety of reasons. Some of these reasons have to do with Earth’s  atmosphere . The climate change brought by El Niño, which relies on winds and ocean currents, is an example of natural atmospheric changes. Natural climate change can also be affected by forces outside Earth’s atmosphere. For instance, the 100,000-year cycles of ice ages are probably related to changes in the tilt of Earth’s  axis  and the shape of its  orbit  around the sun. Those planetary factors change slowly over time and affect how much of the sun’s energy reaches different parts of the world in different seasons.

The impact of large  meteorites on Earth could also cause climate change . The impact of a meteor would send millions of tons of  debris  into the atmosphere . This debris would block at least some of the sun’s rays, making it cold and dark. This climate change would severely limit what organisms could survive. Many  paleontologists believe the impact of a meteor or comet contributed to the extinction of the dinosaurs .  Dinosaurs simply could not survive in a cool, dark climate . Their bodies could not adjust to the cold, and the dark limited the growth of plants on which they fed.

Plate tectonics  also play a role in climate changes. Earth’s continental plates have moved a great deal over time. More than 200 million years ago, the continents were  merged together as one giant landmass called  Pangaea . As the continents broke apart and moved, their positions on Earth changed, and so did the movements of ocean currents. Both of these changes had effects on climate. Changes in  greenhouse gases in the atmosphere also have an impact on climate change. Gases like  carbon dioxide  trap the sun’s heat in Earth’s atmosphere, causing temperatures on the surface to rise.  Volcanoes —both on land and under the ocean—release greenhouse gases, so if the eruption only reaches the troposphere the additional gases contribute to warming. However, if the eruption is powerful enough to reach the stratosphere particles reflect sunlight back into space causing periods of cooling regionally.

Human Causes of Climate Change Some human activities release greenhouse gases—burning  fossil fuels for  transportation  and  electricity , or using  technology  that increases meat production, for instance. Trees absorb carbon dioxide, so cutting down forests for  timber  or  development  contributes to the greenhouse effect . So do factories that  emit   pollutants into the atmosphere.

Many scientists are worried that these activities are causing dramatic and dangerous changes in Earth’s climate. Average temperatures around the world have risen since about 1880, when scientists began tracking them. The seven warmest years of the 20th century occurred in the 1990s. This warming trend may be a sign that the greenhouse effect is increasing because of human activity. This climate change is often referred to as “ global warming .” Global warming is often linked to the burning of fossil fuels— coal ,  oil , and  natural gas —by industries and cars. Warming is also linked to the destruction of tropical forests. The University of California Riverside and NASA estimate human activity has increased the amount of carbon dioxide in the atmosphere by about 30 percent in the past 150 years. The amount of methane , a potent greehouse gas produced by decomposing plant and animal matter, is also increasing. Increased amounts of methane in Earth’s atmosphere are usually linked to  agricultural development  and industrial technology. As economies grow, populations consume more goods and throw away more materials. Large landfills , filled with decomposing waste, release tons of methane into the atmosphere. Chlorofluorocarbon (CFC) ,  hydrochlorofluorocarbon  (HCFC), and  hydrofluorocarbon  (HFC) chemicals are used in refrigeration and aerosol sprays. These chemicals are also greenhouse gases. Many countries are working to  phase out  their use, and some have laws to prevent companies from manufacturing them.

Global Warming

As the proportion of greenhouse gases in the atmosphere rises, so does the temperature of Earth. Climatologists worry that the global temperature will increase so much that ice caps will begin melting within the next several decades . This would cause the  sea level  to rise. Coastal areas, including many low-lying islands, would be flooded. Severe climate change may bring more severe weather patterns—more  hurricanes ,  typhoons , and  tornadoes . More precipitation would fall in some places and far less in others. Regions where crops now grow could become deserts. As climates change, so do the habitats for living things. Animals that live in an area may become threatened. Many human societies depend on specific crops for food , clothing, and trade . If the climate of an area changes, the people who live there may no longer be able to grow the crops they depend on for survival. Some scientists worry that as Earth warms,  tropical diseases such as  malaria ,  West Nile virus , and  yellow fever  will expand into more  temperate  regions. The temperature will continue to rise unless preventive steps are taken. Most climatologists agree that we must reduce the amount of greenhouse gases released into the atmosphere. There are many ways to do this, including:

• Drive less. Use  public transportation ,  carpool , walk, or ride a bike.
• Fly less. Airplanes produce huge amounts of greenhouse gas emissions .
• Reduce, reuse, and recycle.
• Plant a tree. Trees absorb carbon dioxide, keeping it out of the atmosphere.
• Use less electricity.
• Eat less meat. Cows are one of the biggest methane producers.
• Support alternative energy sources that don’t burn fossil fuels, such as  solar power  and  wind energy .

The climate has changed many times during Earth’s history, but the changes have occurred slowly, over thousands of years. Only since the Industrial Revolution have human activities begun to influence climate—and scientists are still working to understand what the  consequences might be.

Cool Warming Could the current phase of climate change cause another Little Ice Age? As strange as it sounds, some scientists believe it could. If melting glaciers release large amounts of freshwater into the oceans, this could disrupt the ocean conveyor belt, an important circulation system that moves seawater around the globe. Stopping this cycle could possibly cause cooling of 3 to 5 degrees Celsius (5-9 degrees Fahrenheit) in the ocean and atmosphere.

Early Squirrels The North American red squirrel has started breeding earlier in the year as a result of climate change. Food becomes available to the squirrels earlier because of warmer winters.

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Factors Affecting Global Climate

Earth is a dynamic planet, constantly undergoing change driven by internal and external forces. Currents of magma within our planet move the plates that form the continental crust in a constant process that builds mountains and creates valleys. These valleys may eventually become lakes, seas, and oceans. On the surface, the greatest factor affecting Earth is sunlight. Sun provides energy for living organisms, and it drives our planet's weather and climate by creating temperature gradients in the atmosphere and oceans.

Atmospheric Circulation

The sun's rays provide both light and heat to Earth, and regions that receive greater exposure warm to a greater extent. This is particularly true of the tropics, which experience less seasonal variation in incident sunlight. Moisture-laden tropical air warms, becomes less dense, and rises. But as air reaches the upper levels of the atmosphere, it cools. Water molecules condense to form clouds and eventually fall as rain. Warm air rising from Earth's surface pushes the air mass away from the equator, and releases its moisture as precipitation as it travels pole-ward (Figure 1).

If the Earth did not spin on its axis, this cycle of evaporation, condensation, and precipitation would move water and air along a north-south axis from the equator to the poles. This, however, does not happen. Earth's spin creates three belts of circulation (Figure 2). Air circulates from the tropics to regions approximately 30° north and south latitude, where the air masses sink. This belt of air circulation is referred to as a Hadley cell, after George Hadley, who first described it (Holton 2004). Two additional belts of circulating air exist in the temperate latitudes (between 30° and 60° latitude) and near the poles (between 60° and 90° latitude).

The sinking air mass at 30˚ latitude drives two phenomena: It contributes to the formation of arid climates and drives circulation of air north and south of the tropics. Dry, even desert-like conditions often occur at 30˚ north and south latitude because the descending dry air draws moisture from the soil (Figure 3). As warm air rises in the tropics, cool air is drawn from surrounding areas to fill the void. This creates the trade winds that blow in subtropical regions. But some of the air that descends from the Hadley cell is drawn away from the equator toward the poles. This air mass creates winds that characterize weather patterns in the temperate zones.

Under the influence of Earth's rotation, air returning to Earth's surface is deflected by the Coriolis force, which shifts the flow of air to the right of its initial trajectory in the northern hemisphere and to the left of its trajectory in the southern hemisphere. Winds blowing toward the equator are deflected to the west, creating the easterly trade winds (easterly winds blow from east to west). In the temperate zones, where the winds blow toward the poles, the Coriolis force deflects them toward the east, with prevailing westerlies (blowing from west to east) transporting most weather patterns in these temperate climes (Figure 2).

Ocean Currents

Earth's rotation affects the oceans in a similar manner, setting up currents that flow within the ocean basins. Ocean currents are driven by surface winds, Earth's rotation, and differences in salinity.

Trade winds blow warm surface waters in tropical oceans and seas from east to west. Warm water pools along the west coast of continents, which sets up a temperature gradient across the ocean surface. Under normal conditions, the western Pacific is about 8°C warmer than the eastern Pacific, and this gradient contributes to the formation of clouds and precipitation in Australia, Indonesia, and parts of Africa. Disruption of this temperature gradient creates the event known as El Niño.

Movement of water away from the coast of Peru and Ecuador creates an upwelling, as cold water is drawn from below to fill the space (Figure 4). Similar conditions occur on the west coast of continents in the Atlantic and Indian Oceans. These regions are the primary source of mixing between warmer surface waters and colder deep waters, which ordinarily remain separate. The upwelling of nutrient-rich water contributes to the unusually high biological productivity of the coastal waters in these regions.

Just as Earth's rotation creates the prevailing winds, it creates surface currents within the oceans. Under the influence of the trade winds, surface waters near the equator flow from east to west. As in the atmosphere, the Coriolis force causes water to be deflected away from the equator (northward in the Northern Hemisphere, southward in the Southern Hemisphere). This Coriolis Effect sets up a rotational convection within the oceans, and currents typically flow in a clockwise rotation in the Northern Hemisphere and in a counter-clockwise direction in the Southern Hemisphere. As it reaches the poles, the water cools and sinks. Prevailing winds in northern and southern latitudes help to create cold-water surface currents that flow back toward the equator along the west coast of continents.

Surface waters freeze as they reach the arctic waters of the North Atlantic. The freezing process removes water molecules, but not salt, from the ocean. The result is an increase in the salinity of ocean waters. With increased salinity and decreased temperature comes greater density — water is densest at 4°C — and the water sinks to the ocean floor. This process sets up a large, slow, deep-water "conveyor belt" that transports water along the ocean floor to Antarctica then through the Indian, Pacific, and eventually Atlantic oceans.

Global Climate

The combination of oceanic and atmospheric circulation drives global climate by redistributing heat and moisture. Areas located near the tropics remain warm and relatively wet throughout the year. In temperate regions, variation in solar input drives seasonal changes. In the Northern Hemisphere where land masses are more concentrated, these seasons can involve pronounced changes in temperature. In the Southern Hemisphere where large land masses are located nearer to the equator and the majority of Earth's surface is covered with water, seasonal cycles revolve around the presence and absence of precipitation rather than major swings in temperature.

Global climate patterns are dynamic: They are continually changing in response to solar radiation, atmospheric greenhouse gas concentrations, and other climate forcing factors. Among the more predictable of these changes are cyclical changes in solar radiation reaching the poles. These cycles, first described by Milutin Milankovitch (1941), involve Earth's orbit, tilt, and the precession of the equinoxes.

Earth's elliptical orbit around the sun shifts under the gravitational pull of other planets in our solar system. In a 100,000-year cycle, the orbit shifts from one that is nearly circular to one that is elongated, pulling the planet further from its energy source (Figure 5A). Earth's tilt relative to its orbit changes in a 41,000-year cycle from 21.5° to 24.5°; we are currently in the middle of this cycle with a tilt of 23.5° (Figure 5B). Finally, the axis (north-south orientation) of the Earth wobbles over time. This 23,000-year precession of the equinoxes changes the orientation of the planet relative to its location in orbit (Figure 5C). When all three Milankovitch cycles reinforce each other, they alter solar input and influence oceanic and atmospheric circulation patterns. This can lead to regular periods of cooling and glaciation.

Periods of cooling can be intensified through albedo; the presence of snow and ice reflects incident sunlight and heat, which serves to further cool the planet. In this way, glaciers and polar ice caps continue to grow during periods when incident sunlight is low. As more water becomes locked up as ice, the surface level of oceans drops, which can alter oceanic circulation patterns. In addition, movement of continental land masses through the processes of plate tectonics can shift the flow of water, altering ocean currents and circulation patterns.

As Earth's precession and tilt increase polar exposure to sunlight, rapid melting events can occur. Freed from the grip of ice, soils thaw and previously frozen vegetation decays, releasing both carbon dioxide and methane gas — two noted greenhouse gases — into the atmosphere. Increases in carbon dioxide and methane in the atmosphere help to further warm the earth, and these gases are thought to have contributed to historical rapid warming events.

Biogeography

The current distribution of plants and animals reflects historical changes in both global climatic conditions and the location of land masses. During cold periods, when much of the land was covered in snow and ice, the amount of land available for terrestrial organisms to inhabit decreased, increasing competition for resources. As the ice retreated during warming events, organisms migrated to fill newly-available areas, and many species flourished under the new environmental conditions. Over time, organisms evolved adaptations that better enabled them to exploit their new surroundings. Some of those adaptations persist in their modern-day descendants.

While climatic conditions were changing, so were the locations of large land masses as they shifted under the influence of magma currents beneath the crust. Continental collisions built mountain ranges and widening rifts became seas, both of which served to create barriers to organismal dispersal, restricting the ability of organisms to migrate. Restricted to smaller areas, organisms evolved traits that best suited them to the environmental conditions of their continent and region.

Today we recognize six biogeographic realms — Nearctic, Palearctic, Neotropical, Ethiopian, Oriental, and Australian — in which animals exhibit features distinctive to that region (Figure 6). Realms that have experienced barriers to dispersal for longer periods of time contain animals with more distinctive traits. One of the best examples of this can be seen in the marsupial mammals of the Australian Region, which has a long history of isolation from other continents.

References and Recommended Reading

Broecker, W. The great ocean conveyor. Oceanography 4 , 79–89 (1991).

Brown, J. H. & Lomolino, M. V. Biogeography , 2nd ed. Sunderland, MA: Sinauer Associates, 1998.

Campbell, N. A. et al . Biology , 7th ed. San Fransisco CA: Pearson, 2005.

Ekman, V. W. On the influence of the Earth's rotation on ocean currents. Arckiv för Matematik, Astronomi och Fysik 2 , 1–52 (1905).

Gross, M. G. Oceanography: A View of Earth . Englewood Cliffs, NJ: Prentice Hall, 1993)

Holton, J. R. An Introduction to Dynamical Meteorology , 4th ed. Burlington, MA: Elsevier Academic Press, 2004.

Lutgens, F. K. et al . The Atmosphere: An Introduction to Meterorology , 8th ed. Englewood Cliffs, NJ: Prentice Hall, 2001.

Milankovitch, Milutin. Canon of Insolation and the Ice Age Problem . Belgrade: Zavod za Udz̆benike i Nastavna Sredstva. 1941.

National Oceanic and Atmospheric Administration. NOAA Tropical Atmosphere Ocean Project .

Pidwirny, M. "Surface and Subsurface Ocean Currents." In Fundamentals of Physical Geography , 2nd ed. (2006).

Ruddiman, W. F. Earth's Climate: Past and Future , 2nd ed. New York, NY: W. H. Freeman and Company, 2008.

Stowe, K. S. Ocean Science . New York, NY: John Wiley & Sons, 1979.

Trefil, J. & Hazen, R. M. The Sciences: An Integrated Approach , 4th ed. New York, NY: John Wiley & Sons, 2004.

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The Science of Climate Change Explained: Facts, Evidence and Proof

Definitive answers to the big questions.

Credit... Photo Illustration by Andrea D'Aquino

Supported by

By Julia Rosen

Ms. Rosen is a journalist with a Ph.D. in geology. Her research involved studying ice cores from Greenland and Antarctica to understand past climate changes.

• Published April 19, 2021 Updated Nov. 6, 2021

The science of climate change is more solid and widely agreed upon than you might think. But the scope of the topic, as well as rampant disinformation, can make it hard to separate fact from fiction. Here, we’ve done our best to present you with not only the most accurate scientific information, but also an explanation of how we know it.

How do we know climate change is really happening?

How much agreement is there among scientists about climate change, do we really only have 150 years of climate data how is that enough to tell us about centuries of change, how do we know climate change is caused by humans, since greenhouse gases occur naturally, how do we know they’re causing earth’s temperature to rise, why should we be worried that the planet has warmed 2°f since the 1800s, is climate change a part of the planet’s natural warming and cooling cycles, how do we know global warming is not because of the sun or volcanoes, how can winters and certain places be getting colder if the planet is warming, wildfires and bad weather have always happened. how do we know there’s a connection to climate change, how bad are the effects of climate change going to be, what will it cost to do something about climate change, versus doing nothing.

Climate change is often cast as a prediction made by complicated computer models. But the scientific basis for climate change is much broader, and models are actually only one part of it (and, for what it’s worth, they’re surprisingly accurate ).

For more than a century , scientists have understood the basic physics behind why greenhouse gases like carbon dioxide cause warming. These gases make up just a small fraction of the atmosphere but exert outsized control on Earth’s climate by trapping some of the planet’s heat before it escapes into space. This greenhouse effect is important: It’s why a planet so far from the sun has liquid water and life!

However, during the Industrial Revolution, people started burning coal and other fossil fuels to power factories, smelters and steam engines, which added more greenhouse gases to the atmosphere. Ever since, human activities have been heating the planet.

We know this is true thanks to an overwhelming body of evidence that begins with temperature measurements taken at weather stations and on ships starting in the mid-1800s. Later, scientists began tracking surface temperatures with satellites and looking for clues about climate change in geologic records. Together, these data all tell the same story: Earth is getting hotter.

Average global temperatures have increased by 2.2 degrees Fahrenheit, or 1.2 degrees Celsius, since 1880, with the greatest changes happening in the late 20th century. Land areas have warmed more than the sea surface and the Arctic has warmed the most — by more than 4 degrees Fahrenheit just since the 1960s. Temperature extremes have also shifted. In the United States, daily record highs now outnumber record lows two-to-one.

Where it was cooler or warmer in 2020 compared with the middle of the 20th century

This warming is unprecedented in recent geologic history. A famous illustration, first published in 1998 and often called the hockey-stick graph, shows how temperatures remained fairly flat for centuries (the shaft of the stick) before turning sharply upward (the blade). It’s based on data from tree rings, ice cores and other natural indicators. And the basic picture , which has withstood decades of scrutiny from climate scientists and contrarians alike, shows that Earth is hotter today than it’s been in at least 1,000 years, and probably much longer.

In fact, surface temperatures actually mask the true scale of climate change, because the ocean has absorbed 90 percent of the heat trapped by greenhouse gases . Measurements collected over the last six decades by oceanographic expeditions and networks of floating instruments show that every layer of the ocean is warming up. According to one study , the ocean has absorbed as much heat between 1997 and 2015 as it did in the previous 130 years.

We also know that climate change is happening because we see the effects everywhere. Ice sheets and glaciers are shrinking while sea levels are rising. Arctic sea ice is disappearing. In the spring, snow melts sooner and plants flower earlier. Animals are moving to higher elevations and latitudes to find cooler conditions. And droughts, floods and wildfires have all gotten more extreme. Models predicted many of these changes, but observations show they are now coming to pass.

Back to top .

There’s no denying that scientists love a good, old-fashioned argument. But when it comes to climate change, there is virtually no debate: Numerous studies have found that more than 90 percent of scientists who study Earth’s climate agree that the planet is warming and that humans are the primary cause. Most major scientific bodies, from NASA to the World Meteorological Organization , endorse this view. That’s an astounding level of consensus given the contrarian, competitive nature of the scientific enterprise, where questions like what killed the dinosaurs remain bitterly contested .

Scientific agreement about climate change started to emerge in the late 1980s, when the influence of human-caused warming began to rise above natural climate variability. By 1991, two-thirds of earth and atmospheric scientists surveyed for an early consensus study said that they accepted the idea of anthropogenic global warming. And by 1995, the Intergovernmental Panel on Climate Change, a famously conservative body that periodically takes stock of the state of scientific knowledge, concluded that “the balance of evidence suggests that there is a discernible human influence on global climate.” Currently, more than 97 percent of publishing climate scientists agree on the existence and cause of climate change (as does nearly 60 percent of the general population of the United States).

So where did we get the idea that there’s still debate about climate change? A lot of it came from coordinated messaging campaigns by companies and politicians that opposed climate action. Many pushed the narrative that scientists still hadn’t made up their minds about climate change, even though that was misleading. Frank Luntz, a Republican consultant, explained the rationale in an infamous 2002 memo to conservative lawmakers: “Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly,” he wrote. Questioning consensus remains a common talking point today, and the 97 percent figure has become something of a lightning rod .

To bolster the falsehood of lingering scientific doubt, some people have pointed to things like the Global Warming Petition Project, which urged the United States government to reject the Kyoto Protocol of 1997, an early international climate agreement. The petition proclaimed that climate change wasn’t happening, and even if it were, it wouldn’t be bad for humanity. Since 1998, more than 30,000 people with science degrees have signed it. However, nearly 90 percent of them studied something other than Earth, atmospheric or environmental science, and the signatories included just 39 climatologists. Most were engineers, doctors, and others whose training had little to do with the physics of the climate system.

A few well-known researchers remain opposed to the scientific consensus. Some, like Willie Soon, a researcher affiliated with the Harvard-Smithsonian Center for Astrophysics, have ties to the fossil fuel industry . Others do not, but their assertions have not held up under the weight of evidence. At least one prominent skeptic, the physicist Richard Muller, changed his mind after reassessing historical temperature data as part of the Berkeley Earth project. His team’s findings essentially confirmed the results he had set out to investigate, and he came away firmly convinced that human activities were warming the planet. “Call me a converted skeptic,” he wrote in an Op-Ed for the Times in 2012.

Mr. Luntz, the Republican pollster, has also reversed his position on climate change and now advises politicians on how to motivate climate action.

A final note on uncertainty: Denialists often use it as evidence that climate science isn’t settled. However, in science, uncertainty doesn’t imply a lack of knowledge. Rather, it’s a measure of how well something is known. In the case of climate change, scientists have found a range of possible future changes in temperature, precipitation and other important variables — which will depend largely on how quickly we reduce emissions. But uncertainty does not undermine their confidence that climate change is real and that people are causing it.

Earth’s climate is inherently variable. Some years are hot and others are cold, some decades bring more hurricanes than others, some ancient droughts spanned the better part of centuries. Glacial cycles operate over many millenniums. So how can scientists look at data collected over a relatively short period of time and conclude that humans are warming the planet? The answer is that the instrumental temperature data that we have tells us a lot, but it’s not all we have to go on.

Historical records stretch back to the 1880s (and often before), when people began to regularly measure temperatures at weather stations and on ships as they traversed the world’s oceans. These data show a clear warming trend during the 20th century.

Global average temperature compared with the middle of the 20th century

+0.75°C

–0.25°

Some have questioned whether these records could be skewed, for instance, by the fact that a disproportionate number of weather stations are near cities, which tend to be hotter than surrounding areas as a result of the so-called urban heat island effect. However, researchers regularly correct for these potential biases when reconstructing global temperatures. In addition, warming is corroborated by independent data like satellite observations, which cover the whole planet, and other ways of measuring temperature changes.

Much has also been made of the small dips and pauses that punctuate the rising temperature trend of the last 150 years. But these are just the result of natural climate variability or other human activities that temporarily counteract greenhouse warming. For instance, in the mid-1900s, internal climate dynamics and light-blocking pollution from coal-fired power plants halted global warming for a few decades. (Eventually, rising greenhouse gases and pollution-control laws caused the planet to start heating up again.) Likewise, the so-called warming hiatus of the 2000s was partly a result of natural climate variability that allowed more heat to enter the ocean rather than warm the atmosphere. The years since have been the hottest on record .

Still, could the entire 20th century just be one big natural climate wiggle? To address that question, we can look at other kinds of data that give a longer perspective. Researchers have used geologic records like tree rings, ice cores, corals and sediments that preserve information about prehistoric climates to extend the climate record. The resulting picture of global temperature change is basically flat for centuries, then turns sharply upward over the last 150 years. It has been a target of climate denialists for decades. However, study after study has confirmed the results , which show that the planet hasn’t been this hot in at least 1,000 years, and probably longer.

Scientists have studied past climate changes to understand the factors that can cause the planet to warm or cool. The big ones are changes in solar energy, ocean circulation, volcanic activity and the amount of greenhouse gases in the atmosphere. And they have each played a role at times.

For example, 300 years ago, a combination of reduced solar output and increased volcanic activity cooled parts of the planet enough that Londoners regularly ice skated on the Thames . About 12,000 years ago, major changes in Atlantic circulation plunged the Northern Hemisphere into a frigid state. And 56 million years ago, a giant burst of greenhouse gases, from volcanic activity or vast deposits of methane (or both), abruptly warmed the planet by at least 9 degrees Fahrenheit, scrambling the climate, choking the oceans and triggering mass extinctions.

In trying to determine the cause of current climate changes, scientists have looked at all of these factors . The first three have varied a bit over the last few centuries and they have quite likely had modest effects on climate , particularly before 1950. But they cannot account for the planet’s rapidly rising temperature, especially in the second half of the 20th century, when solar output actually declined and volcanic eruptions exerted a cooling effect.

That warming is best explained by rising greenhouse gas concentrations . Greenhouse gases have a powerful effect on climate (see the next question for why). And since the Industrial Revolution, humans have been adding more of them to the atmosphere, primarily by extracting and burning fossil fuels like coal, oil and gas, which releases carbon dioxide.

Bubbles of ancient air trapped in ice show that, before about 1750, the concentration of carbon dioxide in the atmosphere was roughly 280 parts per million. It began to rise slowly and crossed the 300 p.p.m. threshold around 1900. CO2 levels then accelerated as cars and electricity became big parts of modern life, recently topping 420 p.p.m . The concentration of methane, the second most important greenhouse gas, has more than doubled. We’re now emitting carbon much faster than it was released 56 million years ago .

30 billion metric tons

Carbon dioxide emitted worldwide 1850-2017

Rest of world

Other developed

European Union

Developed economies

Other countries

United States

E.U. and U.K.

These rapid increases in greenhouse gases have caused the climate to warm abruptly. In fact, climate models suggest that greenhouse warming can explain virtually all of the temperature change since 1950. According to the most recent report by the Intergovernmental Panel on Climate Change, which assesses published scientific literature, natural drivers and internal climate variability can only explain a small fraction of late-20th century warming.

Another study put it this way: The odds of current warming occurring without anthropogenic greenhouse gas emissions are less than 1 in 100,000 .

But greenhouse gases aren’t the only climate-altering compounds people put into the air. Burning fossil fuels also produces particulate pollution that reflects sunlight and cools the planet. Scientists estimate that this pollution has masked up to half of the greenhouse warming we would have otherwise experienced.

Greenhouse gases like water vapor and carbon dioxide serve an important role in the climate. Without them, Earth would be far too cold to maintain liquid water and humans would not exist!

Here’s how it works: the planet’s temperature is basically a function of the energy the Earth absorbs from the sun (which heats it up) and the energy Earth emits to space as infrared radiation (which cools it down). Because of their molecular structure, greenhouse gases temporarily absorb some of that outgoing infrared radiation and then re-emit it in all directions, sending some of that energy back toward the surface and heating the planet . Scientists have understood this process since the 1850s .

Greenhouse gas concentrations have varied naturally in the past. Over millions of years, atmospheric CO2 levels have changed depending on how much of the gas volcanoes belched into the air and how much got removed through geologic processes. On time scales of hundreds to thousands of years, concentrations have changed as carbon has cycled between the ocean, soil and air.

Today, however, we are the ones causing CO2 levels to increase at an unprecedented pace by taking ancient carbon from geologic deposits of fossil fuels and putting it into the atmosphere when we burn them. Since 1750, carbon dioxide concentrations have increased by almost 50 percent. Methane and nitrous oxide, other important anthropogenic greenhouse gases that are released mainly by agricultural activities, have also spiked over the last 250 years.

We know based on the physics described above that this should cause the climate to warm. We also see certain telltale “fingerprints” of greenhouse warming. For example, nights are warming even faster than days because greenhouse gases don’t go away when the sun sets. And upper layers of the atmosphere have actually cooled, because more energy is being trapped by greenhouse gases in the lower atmosphere.

We also know that we are the cause of rising greenhouse gas concentrations — and not just because we can measure the CO2 coming out of tailpipes and smokestacks. We can see it in the chemical signature of the carbon in CO2.

Carbon comes in three different masses: 12, 13 and 14. Things made of organic matter (including fossil fuels) tend to have relatively less carbon-13. Volcanoes tend to produce CO2 with relatively more carbon-13. And over the last century, the carbon in atmospheric CO2 has gotten lighter, pointing to an organic source.

We can tell it’s old organic matter by looking for carbon-14, which is radioactive and decays over time. Fossil fuels are too ancient to have any carbon-14 left in them, so if they were behind rising CO2 levels, you would expect the amount of carbon-14 in the atmosphere to drop, which is exactly what the data show .

It’s important to note that water vapor is the most abundant greenhouse gas in the atmosphere. However, it does not cause warming; instead it responds to it . That’s because warmer air holds more moisture, which creates a snowball effect in which human-caused warming allows the atmosphere to hold more water vapor and further amplifies climate change. This so-called feedback cycle has doubled the warming caused by anthropogenic greenhouse gas emissions.

A common source of confusion when it comes to climate change is the difference between weather and climate. Weather is the constantly changing set of meteorological conditions that we experience when we step outside, whereas climate is the long-term average of those conditions, usually calculated over a 30-year period. Or, as some say: Weather is your mood and climate is your personality.

So while 2 degrees Fahrenheit doesn’t represent a big change in the weather, it’s a huge change in climate. As we’ve already seen, it’s enough to melt ice and raise sea levels, to shift rainfall patterns around the world and to reorganize ecosystems, sending animals scurrying toward cooler habitats and killing trees by the millions.

It’s also important to remember that two degrees represents the global average, and many parts of the world have already warmed by more than that. For example, land areas have warmed about twice as much as the sea surface. And the Arctic has warmed by about 5 degrees. That’s because the loss of snow and ice at high latitudes allows the ground to absorb more energy, causing additional heating on top of greenhouse warming.

Relatively small long-term changes in climate averages also shift extremes in significant ways. For instance, heat waves have always happened, but they have shattered records in recent years. In June of 2020, a town in Siberia registered temperatures of 100 degrees . And in Australia, meteorologists have added a new color to their weather maps to show areas where temperatures exceed 125 degrees. Rising sea levels have also increased the risk of flooding because of storm surges and high tides. These are the foreshocks of climate change.

And we are in for more changes in the future — up to 9 degrees Fahrenheit of average global warming by the end of the century, in the worst-case scenario . For reference, the difference in global average temperatures between now and the peak of the last ice age, when ice sheets covered large parts of North America and Europe, is about 11 degrees Fahrenheit.

Under the Paris Climate Agreement, which President Biden recently rejoined, countries have agreed to try to limit total warming to between 1.5 and 2 degrees Celsius, or 2.7 and 3.6 degrees Fahrenheit, since preindustrial times. And even this narrow range has huge implications . According to scientific studies, the difference between 2.7 and 3.6 degrees Fahrenheit will very likely mean the difference between coral reefs hanging on or going extinct, and between summer sea ice persisting in the Arctic or disappearing completely. It will also determine how many millions of people suffer from water scarcity and crop failures, and how many are driven from their homes by rising seas. In other words, one degree Fahrenheit makes a world of difference.

Earth’s climate has always changed. Hundreds of millions of years ago, the entire planet froze . Fifty million years ago, alligators lived in what we now call the Arctic . And for the last 2.6 million years, the planet has cycled between ice ages when the planet was up to 11 degrees cooler and ice sheets covered much of North America and Europe, and milder interglacial periods like the one we’re in now.

Climate denialists often point to these natural climate changes as a way to cast doubt on the idea that humans are causing climate to change today. However, that argument rests on a logical fallacy. It’s like “seeing a murdered body and concluding that people have died of natural causes in the past, so the murder victim must also have died of natural causes,” a team of social scientists wrote in The Debunking Handbook , which explains the misinformation strategies behind many climate myths.

Indeed, we know that different mechanisms caused the climate to change in the past. Glacial cycles, for example, were triggered by periodic variations in Earth’s orbit , which take place over tens of thousands of years and change how solar energy gets distributed around the globe and across the seasons.

These orbital variations don’t affect the planet’s temperature much on their own. But they set off a cascade of other changes in the climate system; for instance, growing or melting vast Northern Hemisphere ice sheets and altering ocean circulation. These changes, in turn, affect climate by altering the amount of snow and ice, which reflect sunlight, and by changing greenhouse gas concentrations. This is actually part of how we know that greenhouse gases have the ability to significantly affect Earth’s temperature.

For at least the last 800,000 years , atmospheric CO2 concentrations oscillated between about 180 parts per million during ice ages and about 280 p.p.m. during warmer periods, as carbon moved between oceans, forests, soils and the atmosphere. These changes occurred in lock step with global temperatures, and are a major reason the entire planet warmed and cooled during glacial cycles, not just the frozen poles.

Today, however, CO2 levels have soared to 420 p.p.m. — the highest they’ve been in at least three million years . The concentration of CO2 is also increasing about 100 times faster than it did at the end of the last ice age. This suggests something else is going on, and we know what it is: Since the Industrial Revolution, humans have been burning fossil fuels and releasing greenhouse gases that are heating the planet now (see Question 5 for more details on how we know this, and Questions 4 and 8 for how we know that other natural forces aren’t to blame).

Over the next century or two, societies and ecosystems will experience the consequences of this climate change. But our emissions will have even more lasting geologic impacts: According to some studies, greenhouse gas levels may have already warmed the planet enough to delay the onset of the next glacial cycle for at least an additional 50,000 years.

The sun is the ultimate source of energy in Earth’s climate system, so it’s a natural candidate for causing climate change. And solar activity has certainly changed over time. We know from satellite measurements and other astronomical observations that the sun’s output changes on 11-year cycles. Geologic records and sunspot numbers, which astronomers have tracked for centuries, also show long-term variations in the sun’s activity, including some exceptionally quiet periods in the late 1600s and early 1800s.

We know that, from 1900 until the 1950s, solar irradiance increased. And studies suggest that this had a modest effect on early 20th century climate, explaining up to 10 percent of the warming that’s occurred since the late 1800s. However, in the second half of the century, when the most warming occurred, solar activity actually declined . This disparity is one of the main reasons we know that the sun is not the driving force behind climate change.

Another reason we know that solar activity hasn’t caused recent warming is that, if it had, all the layers of the atmosphere should be heating up. Instead, data show that the upper atmosphere has actually cooled in recent decades — a hallmark of greenhouse warming .

So how about volcanoes? Eruptions cool the planet by injecting ash and aerosol particles into the atmosphere that reflect sunlight. We’ve observed this effect in the years following large eruptions. There are also some notable historical examples, like when Iceland’s Laki volcano erupted in 1783, causing widespread crop failures in Europe and beyond, and the “ year without a summer ,” which followed the 1815 eruption of Mount Tambora in Indonesia.

Since volcanoes mainly act as climate coolers, they can’t really explain recent warming. However, scientists say that they may also have contributed slightly to rising temperatures in the early 20th century. That’s because there were several large eruptions in the late 1800s that cooled the planet, followed by a few decades with no major volcanic events when warming caught up. During the second half of the 20th century, though, several big eruptions occurred as the planet was heating up fast. If anything, they temporarily masked some amount of human-caused warming.

The second way volcanoes can impact climate is by emitting carbon dioxide. This is important on time scales of millions of years — it’s what keeps the planet habitable (see Question 5 for more on the greenhouse effect). But by comparison to modern anthropogenic emissions, even big eruptions like Krakatoa and Mount St. Helens are just a drop in the bucket. After all, they last only a few hours or days, while we burn fossil fuels 24-7. Studies suggest that, today, volcanoes account for 1 to 2 percent of total CO2 emissions.

When a big snowstorm hits the United States, climate denialists can try to cite it as proof that climate change isn’t happening. In 2015, Senator James Inhofe, an Oklahoma Republican, famously lobbed a snowball in the Senate as he denounced climate science. But these events don’t actually disprove climate change.

While there have been some memorable storms in recent years, winters are actually warming across the world. In the United States, average temperatures in December, January and February have increased by about 2.5 degrees this century.

On the flip side, record cold days are becoming less common than record warm days. In the United States, record highs now outnumber record lows two-to-one . And ever-smaller areas of the country experience extremely cold winter temperatures . (The same trends are happening globally.)

So what’s with the blizzards? Weather always varies, so it’s no surprise that we still have severe winter storms even as average temperatures rise. However, some studies suggest that climate change may be to blame. One possibility is that rapid Arctic warming has affected atmospheric circulation, including the fast-flowing, high-altitude air that usually swirls over the North Pole (a.k.a. the Polar Vortex ). Some studies suggest that these changes are bringing more frigid temperatures to lower latitudes and causing weather systems to stall , allowing storms to produce more snowfall. This may explain what we’ve experienced in the U.S. over the past few decades, as well as a wintertime cooling trend in Siberia , although exactly how the Arctic affects global weather remains a topic of ongoing scientific debate .

Climate change may also explain the apparent paradox behind some of the other places on Earth that haven’t warmed much. For instance, a splotch of water in the North Atlantic has cooled in recent years, and scientists say they suspect that may be because ocean circulation is slowing as a result of freshwater streaming off a melting Greenland . If this circulation grinds almost to a halt, as it’s done in the geologic past, it would alter weather patterns around the world.

Not all cold weather stems from some counterintuitive consequence of climate change. But it’s a good reminder that Earth’s climate system is complex and chaotic, so the effects of human-caused changes will play out differently in different places. That’s why “global warming” is a bit of an oversimplification. Instead, some scientists have suggested that the phenomenon of human-caused climate change would more aptly be called “ global weirding .”

Extreme weather and natural disasters are part of life on Earth — just ask the dinosaurs. But there is good evidence that climate change has increased the frequency and severity of certain phenomena like heat waves, droughts and floods. Recent research has also allowed scientists to identify the influence of climate change on specific events.

Let’s start with heat waves . Studies show that stretches of abnormally high temperatures now happen about five times more often than they would without climate change, and they last longer, too. Climate models project that, by the 2040s, heat waves will be about 12 times more frequent. And that’s concerning since extreme heat often causes increased hospitalizations and deaths, particularly among older people and those with underlying health conditions. In the summer of 2003, for example, a heat wave caused an estimated 70,000 excess deaths across Europe. (Human-caused warming amplified the death toll .)

Climate change has also exacerbated droughts , primarily by increasing evaporation. Droughts occur naturally because of random climate variability and factors like whether El Niño or La Niña conditions prevail in the tropical Pacific. But some researchers have found evidence that greenhouse warming has been affecting droughts since even before the Dust Bowl . And it continues to do so today. According to one analysis , the drought that afflicted the American Southwest from 2000 to 2018 was almost 50 percent more severe because of climate change. It was the worst drought the region had experienced in more than 1,000 years.

Rising temperatures have also increased the intensity of heavy precipitation events and the flooding that often follows. For example, studies have found that, because warmer air holds more moisture, Hurricane Harvey, which struck Houston in 2017, dropped between 15 and 40 percent more rainfall than it would have without climate change.

It’s still unclear whether climate change is changing the overall frequency of hurricanes, but it is making them stronger . And warming appears to favor certain kinds of weather patterns, like the “ Midwest Water Hose ” events that caused devastating flooding across the Midwest in 2019 .

It’s important to remember that in most natural disasters, there are multiple factors at play. For instance, the 2019 Midwest floods occurred after a recent cold snap had frozen the ground solid, preventing the soil from absorbing rainwater and increasing runoff into the Missouri and Mississippi Rivers. These waterways have also been reshaped by levees and other forms of river engineering, some of which failed in the floods.

Wildfires are another phenomenon with multiple causes. In many places, fire risk has increased because humans have aggressively fought natural fires and prevented Indigenous peoples from carrying out traditional burning practices. This has allowed fuel to accumulate that makes current fires worse .

However, climate change still plays a major role by heating and drying forests, turning them into tinderboxes. Studies show that warming is the driving factor behind the recent increases in wildfires; one analysis found that climate change is responsible for doubling the area burned across the American West between 1984 and 2015. And researchers say that warming will only make fires bigger and more dangerous in the future.

It depends on how aggressively we act to address climate change. If we continue with business as usual, by the end of the century, it will be too hot to go outside during heat waves in the Middle East and South Asia . Droughts will grip Central America, the Mediterranean and southern Africa. And many island nations and low-lying areas, from Texas to Bangladesh, will be overtaken by rising seas. Conversely, climate change could bring welcome warming and extended growing seasons to the upper Midwest , Canada, the Nordic countries and Russia . Farther north, however, the loss of snow, ice and permafrost will upend the traditions of Indigenous peoples and threaten infrastructure.

It’s complicated, but the underlying message is simple: unchecked climate change will likely exacerbate existing inequalities . At a national level, poorer countries will be hit hardest, even though they have historically emitted only a fraction of the greenhouse gases that cause warming. That’s because many less developed countries tend to be in tropical regions where additional warming will make the climate increasingly intolerable for humans and crops. These nations also often have greater vulnerabilities, like large coastal populations and people living in improvised housing that is easily damaged in storms. And they have fewer resources to adapt, which will require expensive measures like redesigning cities, engineering coastlines and changing how people grow food.

Already, between 1961 and 2000, climate change appears to have harmed the economies of the poorest countries while boosting the fortunes of the wealthiest nations that have done the most to cause the problem, making the global wealth gap 25 percent bigger than it would otherwise have been. Similarly, the Global Climate Risk Index found that lower income countries — like Myanmar, Haiti and Nepal — rank high on the list of nations most affected by extreme weather between 1999 and 2018. Climate change has also contributed to increased human migration, which is expected to increase significantly .

Even within wealthy countries, the poor and marginalized will suffer the most. People with more resources have greater buffers, like air-conditioners to keep their houses cool during dangerous heat waves, and the means to pay the resulting energy bills. They also have an easier time evacuating their homes before disasters, and recovering afterward. Lower income people have fewer of these advantages, and they are also more likely to live in hotter neighborhoods and work outdoors, where they face the brunt of climate change.

These inequalities will play out on an individual, community, and regional level. A 2017 analysis of the U.S. found that, under business as usual, the poorest one-third of counties, which are concentrated in the South, will experience damages totaling as much as 20 percent of gross domestic product, while others, mostly in the northern part of the country, will see modest economic gains. Solomon Hsiang, an economist at University of California, Berkeley, and the lead author of the study, has said that climate change “may result in the largest transfer of wealth from the poor to the rich in the country’s history.”

Even the climate “winners” will not be immune from all climate impacts, though. Desirable locations will face an influx of migrants. And as the coronavirus pandemic has demonstrated, disasters in one place quickly ripple across our globalized economy. For instance, scientists expect climate change to increase the odds of multiple crop failures occurring at the same time in different places, throwing the world into a food crisis .

On top of that, warmer weather is aiding the spread of infectious diseases and the vectors that transmit them, like ticks and mosquitoes . Research has also identified troubling correlations between rising temperatures and increased interpersonal violence , and climate change is widely recognized as a “threat multiplier” that increases the odds of larger conflicts within and between countries. In other words, climate change will bring many changes that no amount of money can stop. What could help is taking action to limit warming.

One of the most common arguments against taking aggressive action to combat climate change is that doing so will kill jobs and cripple the economy. But this implies that there’s an alternative in which we pay nothing for climate change. And unfortunately, there isn’t. In reality, not tackling climate change will cost a lot , and cause enormous human suffering and ecological damage, while transitioning to a greener economy would benefit many people and ecosystems around the world.

Let’s start with how much it will cost to address climate change. To keep warming well below 2 degrees Celsius, the goal of the Paris Climate Agreement, society will have to reach net zero greenhouse gas emissions by the middle of this century. That will require significant investments in things like renewable energy, electric cars and charging infrastructure, not to mention efforts to adapt to hotter temperatures, rising sea-levels and other unavoidable effects of current climate changes. And we’ll have to make changes fast.

Estimates of the cost vary widely. One recent study found that keeping warming to 2 degrees Celsius would require a total investment of between $4 trillion and $60 trillion, with a median estimate of $16 trillion, while keeping warming to 1.5 degrees Celsius could cost between $10 trillion and $100 trillion, with a median estimate of $30 trillion. (For reference, the entire world economy was about $88 trillion in 2019.) Other studies have found that reaching net zero will require annual investments ranging from less than 1.5 percent of global gross domestic product to as much as 4 percent . That’s a lot, but within the range of historical energy investments in countries like the U.S.

Now, let’s consider the costs of unchecked climate change, which will fall hardest on the most vulnerable. These include damage to property and infrastructure from sea-level rise and extreme weather, death and sickness linked to natural disasters, pollution and infectious disease, reduced agricultural yields and lost labor productivity because of rising temperatures, decreased water availability and increased energy costs, and species extinction and habitat destruction. Dr. Hsiang, the U.C. Berkeley economist, describes it as “death by a thousand cuts.”

As a result, climate damages are hard to quantify. Moody’s Analytics estimates that even 2 degrees Celsius of warming will cost the world $69 trillion by 2100, and economists expect the toll to keep rising with the temperature. In a recent survey , economists estimated the cost would equal 5 percent of global G.D.P. at 3 degrees Celsius of warming (our trajectory under current policies) and 10 percent for 5 degrees Celsius. Other research indicates that, if current warming trends continue, global G.D.P. per capita will decrease between 7 percent and 23 percent by the end of the century — an economic blow equivalent to multiple coronavirus pandemics every year. And some fear these are vast underestimates .

Already, studies suggest that climate change has slashed incomes in the poorest countries by as much as 30 percent and reduced global agricultural productivity by 21 percent since 1961. Extreme weather events have also racked up a large bill. In 2020, in the United States alone, climate-related disasters like hurricanes, droughts, and wildfires caused nearly $100 billion in damages to businesses, property and infrastructure, compared to an average of $18 billion per year in the 1980s.

Given the steep price of inaction, many economists say that addressing climate change is a better deal . It’s like that old saying: an ounce of prevention is worth a pound of cure. In this case, limiting warming will greatly reduce future damage and inequality caused by climate change. It will also produce so-called co-benefits, like saving one million lives every year by reducing air pollution, and millions more from eating healthier, climate-friendly diets. Some studies even find that meeting the Paris Agreement goals could create jobs and increase global G.D.P . And, of course, reining in climate change will spare many species and ecosystems upon which humans depend — and which many people believe to have their own innate value.

The challenge is that we need to reduce emissions now to avoid damages later, which requires big investments over the next few decades. And the longer we delay, the more we will pay to meet the Paris goals. One recent analysis found that reaching net-zero by 2050 would cost the U.S. almost twice as much if we waited until 2030 instead of acting now. But even if we miss the Paris target, the economics still make a strong case for climate action, because every additional degree of warming will cost us more — in dollars, and in lives.

Veronica Penney contributed reporting.

Illustration photographs by Esther Horvath, Max Whittaker, David Maurice Smith and Talia Herman for The New York Times; Esther Horvath/Alfred-Wegener-Institut

An earlier version of this article misidentified the authors of The Debunking Handbook. It was written by social scientists who study climate communication, not a team of climate scientists.

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Climate Zones of the United States Essay

The types of climate zones, atmospheric currents.

The U.S. is a vast country and is home to almost every type of climate zones. The four types of climate zones generally are polar, temperate, tropical climates, and deserts (Rohli and Vega 180). All of their subtypes can be spotted in the U.S.: from arctic and subarctic in Alaska to tropical in the Hawaiian Islands, California, and Florida. In general, the majority of the territory belongs to a temperate (continental) climate, humid in the east and dry in the west, with hot summers and cold winters.

The tropical climate can be seen in Florida and Hawaii, the warmest regions of the U.S., winters here are warm, and summers are scorching. The desert climate is in Arizona and eastern California where the Death Valley and the Grand Canyon can be found as examples. The polar climate zone with freezing winters and cool summers is influencing the nature of the Northern Interior, Great Lakes, and New England. There are other climate subtypes such as Mediterranean (South Florida), temperate oceanic (Pacific Northwest).

One of the fundamental factors determining the climate in the United States is the presence of atmospheric currents, which carry air masses and moisture from the North Pacific Ocean on the continent. The moist Pacific cyclones abundantly irrigate the northwestern coast of the country with rain or snow (Rohli and Vega 185). As for the southern regions of the U.S., in California, precipitation mainly falls in the fall and winter, so summer is dry and hot there. A barrier arises in the form of the Pacific mountains and the Rocky Mountains on the way the air masses move inland. Because of this, the region of the Intermontane Plateau and the western part of the Great Plains is almost always dry. Also, the climate of the United States of America is greatly influenced by the warm tropical air currents coming here from the Atlantic and the Gulf of Mexico.

Rohli, Robert V., and Anthony J. Vega. Climatology . Jones & Bartlett Learning, 2017.

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What factors affect climate?

Five factors affect climate. These are summarised below.

Temperature range increases with distance from the equator. Also, temperatures decrease as you move away from the equator because the sun’s rays are dispersed over a larger land area as you move away from the equator due to the Earth’s curved surface.

The difference in the concentration of solar energy at the equator and the poles

Temperatures decrease with height as the air is less dense and cannot hold heat as well. As a result, the temperature usually drops by 1°C for every 100 metres in altitude.

If winds have been blown from a hot area, they will raise temperatures. If winds have originated from cold regions, they will lower temperatures. In the UK, winds originating from the south tend to be warm, whereas those from the north bring cold air. Air masses have a significant influence on the climate of the UK.

Air masses affecting the UK – source: Met Office

Distance from the sea (continentality)

Land heats and cools faster than the sea. Therefore coastal areas have a lower temperature range than those areas inland. On the coast, winters are mild, and summers are cool. In inland areas, temperatures are high in the summer and cold in the winter. Despite London and Moscow being on similar lines of latitude, London experiences much milder winters and cooler summers than Moscow due to its proximity to the sea.

Aspect 

Slopes facing the sun are warmer than those that are not. Therefore, south-facing slopes in the northern hemisphere are usually warm. However, slopes facing north in the southern hemisphere are warmest.

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What is climate change mitigation and why is it urgent?

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• Climate change mitigation involves actions to reduce or prevent greenhouse gas emissions from human activities.
• Mitigation efforts include transitioning to renewable energy sources, enhancing energy efficiency, adopting regenerative agricultural practices and protecting and restoring forests and critical ecosystems.
• Effective mitigation requires a whole-of-society approach and structural transformations to reduce emissions and limit global warming to 1.5°C above pre-industrial levels.
• International cooperation, for example through the Paris Agreement, is crucial in guiding and achieving global and national mitigation goals.
• Mitigation efforts face challenges such as the world's deep-rooted dependency on fossil fuels, the increased demand for new mineral resources and the difficulties in revamping our food systems.
• These challenges also offer opportunities to improve resilience and contribute to sustainable development.

What is climate change mitigation?

Climate change mitigation refers to any action taken by governments, businesses or people to reduce or prevent greenhouse gases, or to enhance carbon sinks that remove them from the atmosphere. These gases trap heat from the sun in our planet’s atmosphere, keeping it warm. 

Since the industrial era began, human activities have led to the release of dangerous levels of greenhouse gases, causing global warming and climate change. However, despite unequivocal research about the impact of our activities on the planet’s climate and growing awareness of the severe danger climate change poses to our societies, greenhouse gas emissions keep rising. If we can slow down the rise in greenhouse gases, we can slow down the pace of climate change and avoid its worst consequences.

Reducing greenhouse gases can be achieved by:

• Shifting away from fossil fuels : Fossil fuels are the biggest source of greenhouse gases, so transitioning to modern renewable energy sources like solar, wind and geothermal power, and advancing sustainable modes of transportation, is crucial.
• Improving energy efficiency : Using less energy overall – in buildings, industries, public and private spaces, energy generation and transmission, and transportation – helps reduce emissions. This can be achieved by using thermal comfort standards, better insulation and energy efficient appliances, and by improving building design, energy transmission systems and vehicles.
• Changing agricultural practices : Certain farming methods release high amounts of methane and nitrous oxide, which are potent greenhouse gases. Regenerative agricultural practices – including enhancing soil health, reducing livestock-related emissions, direct seeding techniques and using cover crops – support mitigation, improve resilience and decrease the cost burden on farmers.
• The sustainable management and conservation of forests : Forests act as carbon sinks , absorbing carbon dioxide and reducing the overall concentration of greenhouse gases in the atmosphere. Measures to reduce deforestation and forest degradation are key for climate mitigation and generate multiple additional benefits such as biodiversity conservation and improved water cycles.
• Restoring and conserving critical ecosystems : In addition to forests, ecosystems such as wetlands, peatlands, and grasslands, as well as coastal biomes such as mangrove forests, also contribute significantly to carbon sequestration, while supporting biodiversity and enhancing climate resilience.
• Creating a supportive environment : Investments, policies and regulations that encourage emission reductions, such as incentives, carbon pricing and limits on emissions from key sectors are crucial to driving climate change mitigation.

Photo: Stephane Bellerose/UNDP Mauritius

Photo: La Incre and Lizeth Jurado/PROAmazonia

What is the 1.5°C goal and why do we need to stick to it?

In 2015, 196 Parties to the UN Climate Convention in Paris adopted the Paris Agreement , a landmark international treaty, aimed at curbing global warming and addressing the effects of climate change. Its core ambition is to cap the rise in global average temperatures to well below 2°C above levels observed prior to the industrial era, while pursuing efforts to limit the increase to 1.5°C.

The 1.5°C goal is extremely important, especially for vulnerable communities already experiencing severe climate change impacts. Limiting warming below 1.5°C will translate into less extreme weather events and sea level rise, less stress on food production and water access, less biodiversity and ecosystem loss, and a lower chance of irreversible climate consequences.

To limit global warming to the critical threshold of 1.5°C, it is imperative for the world to undertake significant mitigation action. This requires a reduction in greenhouse gas emissions by 45 percent before 2030 and achieving net-zero emissions by mid-century.

What are the policy instruments that countries can use to drive mitigation?

Everyone has a role to play in climate change mitigation, from individuals adopting sustainable habits and advocating for change to governments implementing regulations, providing incentives and facilitating investments. The private sector, particularly those businesses and companies responsible for causing high emissions, should take a leading role in innovating, funding and driving climate change mitigation solutions. 

International collaboration and technology transfer is also crucial given the global nature and size of the challenge. As the main platform for international cooperation on climate action, the Paris Agreement has set forth a series of responsibilities and policy tools for its signatories. One of the primary instruments for achieving the goals of the treaty is Nationally Determined Contributions (NDCs) . These are the national climate pledges that each Party is required to develop and update every five years. NDCs articulate how each country will contribute to reducing greenhouse gas emissions and enhance climate resilience.   While NDCs include short- to medium-term targets, long-term low emission development strategies (LT-LEDS) are policy tools under the Paris Agreement through which countries must show how they plan to achieve carbon neutrality by mid-century. These strategies define a long-term vision that gives coherence and direction to shorter-term national climate targets.

Photo: Mucyo Serge/UNDP Rwanda

Photo: William Seal/UNDP Sudan

At the same time, the call for climate change mitigation has evolved into a call for reparative action, where high-income countries are urged to rectify past and ongoing contributions to the climate crisis. This approach reflects the UN Framework Convention on Climate Change (UNFCCC) which advocates for climate justice, recognizing the unequal historical responsibility for the climate crisis, emphasizing that wealthier countries, having profited from high-emission activities, bear a greater obligation to lead in mitigating these impacts. This includes not only reducing their own emissions, but also supporting vulnerable countries in their transition to low-emission development pathways.

Another critical aspect is ensuring a just transition for workers and communities that depend on the fossil fuel industry and its many connected industries. This process must prioritize social equity and create alternative employment opportunities as part of the shift towards renewable energy and more sustainable practices.

For emerging economies, innovation and advancements in technology have now demonstrated that robust economic growth can be achieved with clean, sustainable energy sources. By integrating renewable energy technologies such as solar, wind and geothermal power into their growth strategies, these economies can reduce their emissions, enhance energy security and create new economic opportunities and jobs. This shift not only contributes to global mitigation efforts but also sets a precedent for sustainable development.

What are some of the challenges slowing down climate change mitigation efforts?

Mitigating climate change is fraught with complexities, including the global economy's deep-rooted dependency on fossil fuels and the accompanying challenge of eliminating fossil fuel subsidies. This reliance – and the vested interests that have a stake in maintaining it – presents a significant barrier to transitioning to sustainable energy sources.

The shift towards decarbonization and renewable energy is driving increased demand for critical minerals such as copper, lithium, nickel, cobalt, and rare earth metals. Since new mining projects can take up to 15 years to yield output, mineral supply chains could become a bottleneck for decarbonization efforts. In addition, these minerals are predominantly found in a few, mostly low-income countries, which could heighten supply chain vulnerabilities and geopolitical tensions.

Furthermore, due to the significant demand for these minerals and the urgency of the energy transition, the scaled-up investment in the sector has the potential to exacerbate environmental degradation, economic and governance risks, and social inequalities, affecting the rights of Indigenous Peoples, local communities, and workers. Addressing these concerns necessitates implementing social and environmental safeguards, embracing circular economy principles, and establishing and enforcing responsible policies and regulations .

Agriculture is currently the largest driver of deforestation worldwide. A transformation in our food systems to reverse the impact that agriculture has on forests and biodiversity is undoubtedly a complex challenge. But it is also an important opportunity. The latest IPCC report highlights that adaptation and mitigation options related to land, water and food offer the greatest potential in responding to the climate crisis. Shifting to regenerative agricultural practices will not only ensure a healthy, fair and stable food supply for the world’s population, but also help to significantly reduce greenhouse gas emissions.  

Photo: UNDP India

Photo: Nino Zedginidze/UNDP Georgia

What are some examples of climate change mitigation?

In Mauritius , UNDP, with funding from the Green Climate Fund, has supported the government to install battery energy storage capacity that has enabled 50 MW of intermittent renewable energy to be connected to the grid, helping to avoid 81,000 tonnes of carbon dioxide annually. 

In Indonesia , UNDP has been working with the government for over a decade to support sustainable palm oil production. In 2019, the country adopted a National Action Plan on Sustainable Palm Oil, which was collaboratively developed by government, industry and civil society representatives. The plan increased the adoption of practices to minimize the adverse social and environmental effects of palm oil production and to protect forests. Since 2015, 37 million tonnes of direct greenhouse gas emissions have been avoided and 824,000 hectares of land with high conservation value have been protected.

In Moldova and Paraguay , UNDP has helped set up Green City Labs that are helping build more sustainable cities. This is achieved by implementing urban land use and mobility planning, prioritizing energy efficiency in residential buildings, introducing low-carbon public transport, implementing resource-efficient waste management, and switching to renewable energy sources. 

UNDP has supported the governments of Brazil, Costa Rica, Ecuador and Indonesia to implement results-based payments through the REDD+ (Reducing emissions from deforestation and forest degradation in developing countries) framework. These include payments for environmental services and community forest management programmes that channel international climate finance resources to local actors on the ground, specifically forest communities and Indigenous Peoples. 

UNDP is also supporting small island developing states like the Comoros to invest in renewable energy and sustainable infrastructure. Through the Africa Minigrids Program , solar minigrids will be installed in two priority communities, Grand Comore and Moheli, providing energy access through distributed renewable energy solutions to those hardest to reach.

And in South Africa , a UNDP initative to boost energy efficiency awareness among the general population and improve labelling standards has taken over commercial shopping malls.

What is UNDP’s role in supporting climate change mitigation?

UNDP aims to assist countries with their climate change mitigation efforts, guiding them towards sustainable, low-carbon and climate-resilient development. This support is in line with achieving the Sustainable Development Goals (SDGs), particularly those related to affordable and clean energy (SDG7), sustainable cities and communities (SDG11), and climate action (SDG13). Specifically, UNDP’s offer of support includes developing and improving legislation and policy, standards and regulations, capacity building, knowledge dissemination, and financial mobilization for countries to pilot and scale-up mitigation solutions such as renewable energy projects, energy efficiency initiatives and sustainable land-use practices. 

With financial support from the Global Environment Facility and the Green Climate Fund, UNDP has an active portfolio of 94 climate change mitigation projects in 69 countries. These initiatives are not only aimed at reducing greenhouse gas emissions, but also at contributing to sustainable and resilient development pathways.

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Climate Change Essay for Students and Children

500+ words climate change essay.

Climate change refers to the change in the environmental conditions of the earth. This happens due to many internal and external factors. The climatic change has become a global concern over the last few decades. Besides, these climatic changes affect life on the earth in various ways. These climatic changes are having various impacts on the ecosystem and ecology. Due to these changes, a number of species of plants and animals have gone extinct.

When Did it Start?

The climate started changing a long time ago due to human activities but we came to know about it in the last century. During the last century, we started noticing the climatic change and its effect on human life. We started researching on climate change and came to know that the earth temperature is rising due to a phenomenon called the greenhouse effect. The warming up of earth surface causes many ozone depletion, affect our agriculture , water supply, transportation, and several other problems.

Reason Of Climate Change

Although there are hundreds of reason for the climatic change we are only going to discuss the natural and manmade (human) reasons.

Get the huge list of more than 500 Essay Topics and Ideas

Natural Reasons

These include volcanic eruption , solar radiation, tectonic plate movement, orbital variations. Due to these activities, the geographical condition of an area become quite harmful for life to survive. Also, these activities raise the temperature of the earth to a great extent causing an imbalance in nature.

Human Reasons

Man due to his need and greed has done many activities that not only harm the environment but himself too. Many plant and animal species go extinct due to human activity. Human activities that harm the climate include deforestation, using fossil fuel , industrial waste , a different type of pollution and many more. All these things damage the climate and ecosystem very badly. And many species of animals and birds got extinct or on a verge of extinction due to hunting.

Effects Of Climatic Change

These climatic changes have a negative impact on the environment. The ocean level is rising, glaciers are melting, CO2 in the air is increasing, forest and wildlife are declining, and water life is also getting disturbed due to climatic changes. Apart from that, it is calculated that if this change keeps on going then many species of plants and animals will get extinct. And there will be a heavy loss to the environment.

What will be Future?

If we do not do anything and things continue to go on like right now then a day in future will come when humans will become extinct from the surface of the earth. But instead of neglecting these problems we start acting on then we can save the earth and our future.

Although humans mistake has caused great damage to the climate and ecosystem. But, it is not late to start again and try to undo what we have done until now to damage the environment. And if every human start contributing to the environment then we can be sure of our existence in the future.

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Explore historical and projected climate data, climate data by sector, impacts, key vulnerabilities and what adaptation measures are being taken. Explore the overview for a general context of how climate change is affecting Sri Lanka.

• Climate Change Overview

Country Summary

• Climatology
• Trends & Variability
• Mean Projections (CMIP6)
• Extreme Events
• Historical Natural Hazards
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This page presents high-level information for Sri Lanka's climate zones and its seasonal cycle for mean temperature and precipitation for the latest climatology, 1991-2020. Climate zone classifications are derived from the  Köppen-Geiger climate classification system , which divides climates into five main climate groups divided based on seasonal precipitation and temperature patterns. The five main groups are  A  (tropical),  B  (dry),  C  (temperate),  D  (continental), and  E  (polar). All climates except for those in the E group are assigned a seasonal precipitation sub-group (second letter).  Climate classifications are identified by hovering your mouse over the legend. A narrative overview of Sri Lanka's country context and climate is provided following the visualizations.

Sri Lanka is a small island nation lying between 6°N and 10°N latitude and 80°E and 82°E longitude in the Indian Ocean, with a land area of approximately 65,000 square kilometers (km 2 ). The island consists of a mountainous area in the south-central region and a surrounding coastal plain. The climate of Sri Lanka is wet and warm, ideal for forest growth; almost all of the nation’s land area was at one time covered with forests. Over the last century, more than two-thirds of this forest cover, rich in biodiversity, has been removed to accommodate human use. Nonetheless, rich natural resources remain and, alongside its vibrant cultures, contribute to the nation’s successful tourism industry. Approximately a quarter of Sri Lanka’s population are believed to live within the metropolitan area of its commercial capital, Colombo. However, official statistics suggest Sri Lanka’s urban population is relatively low, reportedly 18.6% in 2019. Sri Lanka’s high temperatures, unique and complex hydrological regime, and exposure to extreme climate events make it highly vulnerable to climate change.

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Initial Load

Current slide id:, layers loaded, the usda’s gardening zones shifted. this map shows you what’s changed in vivid   detail.

By Daniel Wood, Connie Hanzhang Jin, Brent Jones and Jeff   Brady

Recently, the USDA updated its plant hardiness map for the first time in 11   years.

If you’re a gardener — and everybody can be a gardener, even on a balcony or a stoop — this is a big   deal!

The updated map opens up new possibilities for home gardeners, but there are limits. Let’s explore how the map has changed and what this means for your   garden.

Enter your city and   state:

Back then, coldest winter temperature was somewhere degrees Fahrenheit on average.

Now, the lowest winter temperature is degrees Fahrenheit on   average.

The new 30-year minimum temperature average was 3.3 degrees F warmer than the previous average, which spanned 1976 to   2005.

Change in lowest winter temperature

+8° F

+9° C

The 2012 USDA hardiness zones were calculated using the average lowest winter temperature for the observation period of 1976-2005. The new zones are calculated using the years 1991-2020. These two observation windows overlap. Colors show the difference between the two 30-year averages for each place on the   map.

Most of the changes across the country are due to the warming   climate.

Winters are warming at a faster pace than other seasons, according to Deke Arndt, director of the National Oceanic and Atmospheric Administration’s National Centers for Environmental   Information.

At the same time, an increase in the amount and quality of data collected at weather stations across the country helped to improve the overall accuracy of temperature readings in recent   years.

What does your hardiness zone tell   you?

Some people might think their hardiness zone tells them which plants they can grow. In reality, it’s a little more   complicated.

Your zone measurement is an average of the coldest yearly temperature in your area over the past 30   years.

Though these temperature estimates differ slightly from the data the USDA used to create the zone map, we’re using them to illustrate how zones are calculated.

However, the temperatures we’re showing here are based on estimates, and in this case they do not align with the more accurate, granular data that the USDA used. The USDA map classifies this area as .

This measurement, which predicts an area’s coldest temperatures, is only useful for plants that have to survive the   winter.

They’re called perennials: You plant them once and they come back after each winter if they’re given the right environment to survive. Think things like trees, shrubs and woody   plants.

Windmill palm

And for predicting winter plant survival, knowing an area’s hardiness zone is a big help to gardeners, says Todd Rounsaville, a horticulturist with the USDA who was involved with creating the new map. He explains that the hardiness zone “is really one of the best predictors of winter survival and plant survival in general in the   landscape.”

He advises gardeners to use the map as one very important tool of many in their risk assessment   toolbox.

“Because the USDA map has really become the industry standard for rating things, it’s pretty rare that you will not see a zone rating on a plant, either on the tag or on a website,” he   says.

Knowing what your average coldest temperature is helps rightsize your expectations about what might grow in your area. Live in Chicago’s Zone 6a ? You can be assured that no citrus plants will survive your winter. Instead, try an apple tree. The apple tree is that kid you grew up with who wore shorts all winter. It needs the cold temperatures to set   fruit.

Live in Miami’s Zone 11a ? No apples for you. Instead, grow dragon   fruit!

What does your hardiness zone not tell you?

On its own, your hardiness zone can’t tell you exactly what to grow in your   area.

For example, parts of these three areas — Juneau, Alaska; Boston, Mass.; and Santa Fe, N.M. — are all in USDA’s Zone   7a .

Juneau, Alaska

Boston, Mass.

Santa Fe, N.M.

“We know intuitively that the same plants can’t grow in these places,” Rounsaville   says.

While Juneau may have relatively temperate winters, it also is extremely wet, averaging over 80 inches of snow a year. Santa Fe, on the other hand, is extremely dry, with much hotter summer temperatures than Juneau. Boston has both temperate winters and summers. It gets a good amount of rain but not nearly enough to sustain Juneau’s rainforest plants. It gets plenty of heat but is colder and wetter in the winter, making it inhospitable for desert dwellers, like cactuses and other   succulents.

But all three cities rarely get below zero degrees each winter, so they are classified as the same   zone.

So when you hear that your zone has changed, here are some things to keep in   mind:

1 The hardiness map says nothing about your extreme lowest temperature

Just because your average lowest winter temperature has changed, doesn’t mean the temperature will never dip below your hardiness   zone.

For example, the average coldest night of the year in St. Louis, Mo., tends to be around 2º F, meaning that it’s in Zone 7a . Because St. Louis has warmed, it moved up from its previous zone rating of 6b .

But notice that this is an average of the coldest temperature St. Louis gets each   winter.

In the past 30 years, the temperature dropped below Zone 7a in at least 11 different   years.

In 2014, the temperature dipped three half zones below St. Louis’ hardiness zone, to -10º F.   Brrrr!

Many common plants that are hardy down to Zone 7 , like rosemary, canna lilies or agave, would suffer significant damage or death from those temperatures, especially during a long cold   snap.

2 The hardiness map says nothing about the frequency of extreme cold   weather

Your poor plants have to stay outside all winter, so the duration and frequency of cold weather matters for plant   survival.

“If you’re naked and you run through a freezer, it’s not going to kill you,” says Andrew Bunting, vice president of horticulture at the Pennsylvania Horticultural Society. “If you run into the freezer and have to stay there for an extended period of time, it’s probably going to kill   you.”

If extreme, out-of-zone weather occurs during a quick cold snap, steps can be taken to protect your plants with temporary blankets or other shelters. Pots can be brought   inside.

But if the extreme lows persist, tender plants will struggle to survive. Your hardiness zone does not take any of this into   account.

3 The hardiness map can’t tell you if your plants will survive the   summer

Summer temperature extremes matter a great deal but are not reflected in the USDA hardiness   map.

Let’s look again at Juneau and Santa Fe, much of which are in Zone 7a . Juneau’s all-time high temperature was 90º F in 1975. Summer days in Santa Fe routinely reach the 90s. Some shade- and cool-weather-loving plants like ferns and hostas will thrive in Juneau but struggle mightily in a place like Santa Fe. Likewise, a cactus accustomed to high temperatures would struggle to thrive in the cooler summer temperatures of Juneau, to say nothing of the overwhelming   rainfall.

Because of this tricky problem, there have been attempts to create a corresponding map that helps gardeners know which plants might survive summer in their   area.

In 1997, the American Horticultural Society released a heat zone map that measured the average number of times per year that the temperature of an area exceeds 86º   F.

But this map didn’t become well known among gardeners. On a recent visit to a plant nursery outside Washington, D.C., nearly every plant tag had a USDA hardiness zone, but only one, out of the several dozen checked, had the AHS heat zone   listed.

Above 86º F, plants from cooler climates rapidly become   stressed.

Because of these complexities, more plant survival factors should be included in the 2023 map, says Tony Avent, who runs Juniper Level Botanic Garden and Plant Delights Nursery in Raleigh,   N.C.

“If [these metrics] had been factored in, that would have given you a much more applicable map,” says Avent, who was a member of the committee that put together the 2012 version of the   map.

“And that’s the part that’s a little   disappointing.”

But including more plant survival factors in the USDA hardiness map runs the risk of creating an overly complicated map and muddying its intended use, Rounsaville   says.

“In a perfect world, we could infinitely break down where plants will grow well, but that’s very hard to do and produce a map that is, you know, coherent but at a local resolution,” Rounsaville   says.

Since the USDA plant hardiness zone can’t tell you everything about how a plant will fare in your garden, it’s a good idea to turn to local plant experts for guidance. Local nurseries and botanical gardens can be great resources for in-depth knowledge of the area and recent warming or cooling   trends.

New plant varieties are constantly being bred with improvements such as increased hardiness, bloom count, bloom length or color   combinations.

Some nursery owners like Avent enjoy experimenting with these plants. He and his team grow many varieties of plants — both typical and unconventional — to figure out which plants they can bring to market in   Raleigh.

“We live to kill plants,” Avent says. He estimates that they’ve killed over 50,000 plant varieties in his career. Every one they kill, they record in a   database.

If my zone changed, can I plant new things   now?

Maybe, and maybe you already did! It’s possible you or your neighbors may have already noticed some of these climatic changes and have been experimenting with plant varieties that were once unusual for your   area.

Keep in mind that the new USDA map is backward looking; it represents changes that have already taken place over the past 30   years.

In the 7a - 7b Philadelphia suburbs, Bunting notes two perennials that he has noticed surviving Philadelphia winters in recent   years.

“It used to be [that] if you had a camellia, it was in a little courtyard with lots of protection, maybe even wrapped [in protective cloth] for the winter.” But now, “It’s perfectly hardy. Same with figs. People used to wrap figs. You don’t have to do that   anymore.”

Of course, your mileage may vary. As Bunting notes, where you plant a perennial in your yard — whether sheltered or in the open — matters. Some areas get southern exposure and lots of sun, others are behind a house, or under a tree. Every yard has many distinct microclimates, and learning how to harness these subtle differences in your yard can help you plant more ambitious varieties with more   confidence.

“Gardeners know that if they’re near paved surfaces or brick and mortar structures, that there’s a lot of radiant heat that those absorb during the day,” Rounsaville says. “And they can really push hardiness zones through the winter to help with plant   survival.”

Aside from local nurseries and botanic gardens, cooperative extension services can be a great place to find local gardening advice. The extension services are part of a national network of local experts who provide advice on everything from agriculture to   gardening.

NPR reached out to services in over 30 areas across the country, and many told us about changes they’ve seen in what they can and can’t plant over the past 15   years.

With that, you have what you need to start a garden. Big or   small.

Happy planting!

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IMF Working Papers

Sovereign environmental, social, and governance (esg) investing: chasing elusive sustainability.

Author/Editor:

Ekaterina Gratcheva ; Bryan Gurhy

Publication Date:

May 17, 2024

Electronic Access:

Free Download . Use the free Adobe Acrobat Reader to view this PDF file

Disclaimer: IMF Working Papers describe research in progress by the author(s) and are published to elicit comments and to encourage debate. The views expressed in IMF Working Papers are those of the author(s) and do not necessarily represent the views of the IMF, its Executive Board, or IMF management.

This paper evaluates the progression of the sovereign ESG landscape since the initial comprehensive assessment of the sector in 2021 in “Demystifying Sovereign ESG” by conducting a comparative analysis of the current sovereign ESG methodologies of commercial ESG providers. The 2021 study articulated the distinct nature of the sovereign ESG segment from corporate ESG and documented fundamental shortcomings in sovereign ESG methodologies, such as the “ingrained income bias”, lack of consensus on environmental performance, and conflation of risk and sustainability objectives. While sovereign ESG methodologies have evolved since 2021, the significant correlation across providers of aggregate, S, and G scores persist. In response to market demand there has been a notable shift towards greater focus on the E pillar against growing heterogeneity on climate and environmental considerations across ESG providers. The findings underscore the disparity between perceptions and realities in implementing a sustainability strategy within the sovereign debt asset class. This necessitates a reevaluation of sovereign ESG scoring methodologies towards outcome-based metrics and urges a globally coordinated effort to establish robust sustainability measurement frameworks.

Working Paper No. 2024/102

9798400277054/1018-5941

WPIEA2024102

Please address any questions about this title to [email protected]

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Photo essay: Inside a sanctuary in Kenya, one of the last safe spaces for birds of prey

The soysambu raptor centre treats hundreds of injured animals, with the hope of releasing them back into the wild.

Simon Thomsett, the director of Soysambu Raptor Centre, is assisted in dressing a bateleur eagle that had a broken wing. All photos: AFP

At the Soysambu Raptor Centre near Nakuru, a city in Kenya , all kinds of injured birds, many of them critically endangered, have found refuge.

Located within the Soysambu Conservancy, a 19,425-hectare conservation centre that borders Lake Nakuru National Park in the west of the country, the centre is one of the few places where birds of prey are safe.

From white-backed vultures to bateleur eagles and owls, the birds here are being treated for a number of issues, including broken wings and bones sustained while jostling for food in the wild or during territorial fights.

While the main aim is to release them into the wild, many birds have permanent injuries and can no longer hunt for prey. The Soysambu Raptor Centre provides them with a safe environment for the rest of their lives, with many raising chicks, which are then released into the wild.

A study published in January by The Peregrine Fund, a US-based non-profit organisation, found the raptor population has fallen by 90 per cent on the African continent over the past 40 years.

The reasons for the decline are numerous.

Vultures and other scavengers have died from eating livestock remains – falling victim to a practice adopted by cattle farmers who poison carcasses to deter lions from approaching their herds.

Deforestation also plays a part as does the proliferation of power lines across Africa that prove fatal for birds who perch on them to hunt prey.

Dozens of towering electricity pylons, many installed in recent years, scar the Soysambu reserve.

The centre consists of 10 enclosures, with a capacity for 15 to 22 birds at a time, according to the Kenya Birds of Prey Trust, which manages the complex.

Established to maintain healthy raptor populations in the country, the Kenya Bird of Prey Trust also runs a number of educational and adoption programmes, working closely with the Kenya Wildlife Service. It also runs the Naivasha Raptor Centre in the nearby Kilimandege Sanctuary.

The remote location of the centres lends itself to raptor rehabilitation, the trust says, which is essential for the slow and monitored releases of birds back into the wild.

Additional input by agencies

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In the campus protests over the war in Gaza, language and rhetoric are—as they have always been when it comes to Israel and Palestine—weapons of mass destruction.

By Zadie Smith

A philosophy without a politics is common enough. Aesthetes, ethicists, novelists—all may be easily critiqued and found wanting on this basis. But there is also the danger of a politics without a philosophy. A politics unmoored, unprincipled, which holds as its most fundamental commitment its own perpetuation. A Realpolitik that believes itself too subtle—or too pragmatic—to deal with such ethical platitudes as thou shalt not kill. Or: rape is a crime, everywhere and always. But sometimes ethical philosophy reënters the arena, as is happening right now on college campuses all over America. I understand the ethics underpinning the protests to be based on two widely recognized principles:

There is an ethical duty to express solidarity with the weak in any situation that involves oppressive power.

If the machinery of oppressive power is to be trained on the weak, then there is a duty to stop the gears by any means necessary.

The first principle sometimes takes the “weak” to mean “whoever has the least power,” and sometimes “whoever suffers most,” but most often a combination of both. The second principle, meanwhile, may be used to defend revolutionary violence, although this interpretation has just as often been repudiated by pacifistic radicals, among whom two of the most famous are, of course, Mahatma Gandhi and Martin Luther King, Jr . In the pacifist’s interpretation, the body that we must place between the gears is not that of our enemy but our own. In doing this, we may pay the ultimate price with our actual bodies, in the non-metaphorical sense. More usually, the risk is to our livelihoods, our reputations, our futures. Before these most recent campus protests began, we had an example of this kind of action in the climate movement. For several years now, many people have been protesting the economic and political machinery that perpetuates climate change, by blocking roads, throwing paint, interrupting plays, and committing many other arrestable offenses that can appear ridiculous to skeptics (or, at the very least, performative), but which in truth represent a level of personal sacrifice unimaginable to many of us.

I experienced this not long ago while participating in an XR climate rally in London. When it came to the point in the proceedings where I was asked by my fellow-protesters whether I’d be willing to commit an arrestable offense—one that would likely lead to a conviction and thus make travelling to the United States difficult or even impossible—I’m ashamed to say that I declined that offer. Turns out, I could not give up my relationship with New York City for the future of the planet. I’d just about managed to stop buying plastic bottles (except when very thirsty) and was trying to fly less. But never to see New York again? What pitiful ethical creatures we are (I am)! Falling at the first hurdle! Anyone who finds themselves rolling their eyes at any young person willing to put their own future into jeopardy for an ethical principle should ask themselves where the limits of their own commitments lie—also whether they’ve bought a plastic bottle or booked a flight recently. A humbling inquiry.

It is difficult to look at the recent Columbia University protests in particular without being reminded of the campus protests of the nineteen-sixties and seventies, some of which happened on the very same lawns. At that time, a cynical political class was forced to observe the spectacle of its own privileged youth standing in solidarity with the weakest historical actors of the moment, a group that included, but was not restricted to, African Americans and the Vietnamese. By placing such people within their ethical zone of interest, young Americans risked both their own academic and personal futures and—in the infamous case of Kent State—their lives. I imagine that the students at Columbia—and protesters on other campuses—fully intend this echo, and, in their unequivocal demand for both a ceasefire and financial divestment from this terrible war, to a certain extent they have achieved it.

But, when I open newspapers and see students dismissing the idea that some of their fellow-students feel, at this particular moment, unsafe on campus, or arguing that such a feeling is simply not worth attending to, given the magnitude of what is occurring in Gaza, I find such sentiments cynical and unworthy of this movement. For it may well be—within the ethical zone of interest that is a campus, which was not so long ago defined as a safe space, delineated by the boundary of a generation’s ethical ideas— it may well be that a Jewish student walking past the tents, who finds herself referred to as a Zionist, and then is warned to keep her distance, is, in that moment, the weakest participant in the zone. If the concept of safety is foundational to these students’ ethical philosophy (as I take it to be), and, if the protests are committed to reinserting ethical principles into a cynical and corrupt politics, it is not right to divest from these same ethics at the very moment they come into conflict with other imperatives. The point of a foundational ethics is that it is not contingent but foundational. That is precisely its challenge to a corrupt politics.

Practicing our ethics in the real world involves a constant testing of them, a recognition that our zones of ethical interest have no fixed boundaries and may need to widen and shrink moment by moment as the situation demands. (Those brave students who—in supporting the ethical necessity of a ceasefire—find themselves at painful odds with family, friends, faith, or community have already made this calculation.) This flexibility can also have the positive long-term political effect of allowing us to comprehend that, although our duty to the weakest is permanent, the role of “the weakest” is not an existential matter independent of time and space but, rather, a contingent situation, continually subject to change. By contrast, there is a dangerous rigidity to be found in the idea that concern for the dreadful situation of the hostages is somehow in opposition to, or incompatible with, the demand for a ceasefire. Surely a ceasefire—as well as being an ethical necessity—is also in the immediate absolute interest of the hostages, a fact that cannot be erased by tearing their posters off walls.

Part of the significance of a student protest is the ways in which it gives young people the opportunity to insist upon an ethical principle while still being, comparatively speaking, a more rational force than the supposed adults in the room, against whose crazed magical thinking they have been forced to define themselves. The equality of all human life was never a self-evident truth in racially segregated America. There was no way to “win” in Vietnam. Hamas will not be “eliminated.” The more than seven million Jewish human beings who live in the gap between the river and the sea will not simply vanish because you think that they should. All of that is just rhetoric. Words. Cathartic to chant, perhaps, but essentially meaningless. A ceasefire, meanwhile, is both a potential reality and an ethical necessity. The monstrous and brutal mass murder of more than eleven hundred people, the majority of them civilians, dozens of them children, on October 7th, has been followed by the monstrous and brutal mass murder (at the time of writing) of a reported fourteen thousand five hundred children. And many more human beings besides, but it’s impossible not to notice that the sort of people who take at face value phrases like “surgical strikes” and “controlled military operation” sometimes need to look at and/or think about dead children specifically in order to refocus their minds on reality.

To send the police in to arrest young people peacefully insisting upon a ceasefire represents a moral injury to us all. To do it with violence is a scandal. How could they do less than protest, in this moment? They are putting their own bodies into the machine. They deserve our support and praise. As to which postwar political arrangement any of these students may favor, and on what basis they favor it—that is all an argument for the day after a ceasefire. One state, two states, river to the sea—in my view, their views have no real weight in this particular moment, or very little weight next to the significance of their collective action, which (if I understand it correctly) is focussed on stopping the flow of money that is funding bloody murder, and calling for a ceasefire, the political euphemism that we use to mark the end of bloody murder. After a ceasefire, the criminal events of the past seven months should be tried and judged, and the infinitely difficult business of creating just, humane, and habitable political structures in the region must begin anew. Right now: ceasefire. And, as we make this demand, we might remind ourselves that a ceasefire is not, primarily, a political demand. Primarily, it is an ethical one.

But it is in the nature of the political that we cannot even attend to such ethical imperatives unless we first know the political position of whoever is speaking. (“Where do you stand on Israel/Palestine?”) In these constructed narratives, there are always a series of shibboleths, that is, phrases that can’t be said, or, conversely, phrases that must be said. Once these words or phrases have been spoken ( river to the sea, existential threat, right to defend, one state, two states, Zionist, colonialist, imperialist, terrorist ) and one’s positionality established, then and only then will the ethics of the question be attended to (or absolutely ignored). The objection may be raised at this point that I am behaving like a novelist, expressing a philosophy without a politics, or making some rarefied point about language and rhetoric while people commit bloody murder. This would normally be my own view, but, in the case of Israel/Palestine, language and rhetoric are and always have been weapons of mass destruction.

It is in fact perhaps the most acute example in the world of the use of words to justify bloody murder, to flatten and erase unbelievably labyrinthine histories, and to deliver the atavistic pleasure of violent simplicity to the many people who seem to believe that merely by saying something they make it so. It is no doubt a great relief to say the word “Hamas” as if it purely and solely described a terrorist entity. A great relief to say “There is no such thing as the Palestinian people” as they stand in front of you. A great relief to say “Zionist colonialist state” and accept those three words as a full and unimpeachable definition of the state of Israel, not only under the disastrous leadership of Benjamin Netanyahu but at every stage of its long and complex history, and also to hear them as a perfectly sufficient description of every man, woman, and child who has ever lived in Israel or happened to find themselves born within it. It is perhaps because we know these simplifications to be impossible that we insist upon them so passionately. They are shibboleths; they describe a people, by defining them against other people—but the people being described are ourselves. The person who says “We must eliminate Hamas” says this not necessarily because she thinks this is a possible outcome on this earth but because this sentence is the shibboleth that marks her membership in the community that says that. The person who uses the word “Zionist” as if that word were an unchanged and unchangeable monolith, meaning exactly the same thing in 2024 and 1948 as it meant in 1890 or 1901 or 1920—that person does not so much bring definitive clarity to the entangled history of Jews and Palestinians as they successfully and soothingly draw a line to mark their own zone of interest and where it ends. And while we all talk, carefully curating our shibboleths, presenting them to others and waiting for them to reveal themselves as with us or against us—while we do all that, bloody murder.

And now here we are, almost at the end of this little stream of words. We’ve arrived at the point at which I must state clearly “where I stand on the issue,” that is, which particular political settlement should, in my own, personal view, occur on the other side of a ceasefire. This is the point wherein—by my stating of a position—you are at once liberated into the simple pleasure of placing me firmly on one side or the other, putting me over there with those who lisp or those who don’t, with the Ephraimites, or with the people of Gilead. Yes, this is the point at which I stake my rhetorical flag in that fantastical, linguistical, conceptual, unreal place—built with words—where rapes are minimized as needs be, and the definition of genocide quibbled over, where the killing of babies is denied, and the precision of drones glorified, where histories are reconsidered or rewritten or analogized or simply ignored, and “Jew” and “colonialist” are synonymous, and “Palestinian” and “terrorist” are synonymous, and language is your accomplice and alibi in all of it. Language euphemized, instrumentalized, and abused, put to work for your cause and only for your cause, so that it does exactly and only what you want it to do. Let me make it easy for you. Put me wherever you want: misguided socialist, toothless humanist, naïve novelist, useful idiot, apologist, denier, ally, contrarian, collaborator, traitor, inexcusable coward. It is my view that my personal views have no more weight than an ear of corn in this particular essay. The only thing that has any weight in this particular essay is the dead. ♦

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