Climate Zones

Blurred Boundaries

Remember the colorful climate map in your school atlas? Global warming is currently redrawing it. A journey across the map to places that are changing faster than ever before.

By Christoph von Eichhorn (Text), Jonas Jetzig (Infographics) and Stefan Kloiber (Development)

April 25, 2025 | reading time: 12 Min.

Climate change does not always appear grim and gloomy. Sometimes it manifests itself in rich yellow, bright red, metallic blue—just like the bee-eater.

Now that May is just around the corner, people in Germany are once again on the lookout to see where these colorful migratory birds will settle down to breed when they arrive in Europe after spending the winter in Africa. Originally, the Mediterranean region was their final destination. But over the past two decades, these heat-loving birds have been moving further and further north.

600 bee-eaters now breed in the Kaiserstuhl region of southern Baden, and last year they were spotted as far north as Kassel and Oberhausen. They are also said to be breeding in Kelheim in Lower Bavaria.

There is a high probability that the bee-eater will migrate further north again this year. This is because the changes in its habitat reflect a shift that has not been seen on Earth for thousands of years.

To illustrate this shift, just open any old school atlas. Somewhere in it you will find the Earth's climate zones, a colorful patchwork of tropical rainforests, savannas, deserts, steppes, tundras, and temperate zones.

And it is very likely that the map is no longer accurate.

A research team has examined climate zones worldwide and concluded that they have shifted dramatically since the beginning of industrialization due to global warming. A cold, continental Germany is a thing of the past, Iceland is becoming greener, and deserts are expanding in Africa. It has become hotter everywhere. At the same time, these changes are relatively minor compared to what the planet – and thus humanity – could face in the course of this century. The division of the world as we know it will change.

This is what the world looked like around the year 1900.

It was the world of Vladimir Köppen. The botanist, who grew up as the child of a German scientist in the Russian Empire, divided the Earth into five classes at the beginning of the 20th century based on typical temperatures and precipitation: tropical, arid, temperate, continental and polar.

His basic idea was that the same climate zones also have roughly the same vegetation—for example, rainforests in the tropics, sparse vegetation in desert regions, or boreal coniferous forests in cold regions.

Later, meteorologist Rudolf Geiger enhanced the system, which is why it is now known as the “Köppen-Geiger classification.”

An international team led by climatologist Hylke Beck, a researcher at King Abdullah University of Science and Technology in Saudi Arabia, has remeasured climate zones using historical and current temperature and precipitation data, accurate to the square kilometer.

In the journal Scientific Data, the climate researchers conclude that since the beginning of the 20th century, approximately five percent of the total land mass have changed to a new Köppen climate class. While polar regions have receded, tropical and arid arid zones are expanding.

Even if global climate targets are met and warming is limited to below two degrees Celsius above pre-industrial levels, this trend is likely to continue. The researchers estimate that a further five percent of the world's landmass will slip into a new climate class by the end of the 21st century, based on an evaluation of 42 climate models.

If the world remains on its current emissions path, which will result in warming of around three degrees by 2100, a further eight percent of land masses would change climate class. An area the size of Argentina, around 2.6 million square kilometers, would then slip from the polar to the continental zone. A region of roughly the same size would no longer have a temperate climate in a few decades, but a tropical one.

And it could get even worse, according to climate researcher Hylke Beck: “Given the current geopolitical situation, the likelihood of even more extreme emission scenarios is increasing, which would further exacerbate these changes and their global impact.” In extreme cases, up to 13 percent of the land area could shift into a new main climate class.

An immediate consequence of the changes is “pressure on plants and animals, forcing them to adapt, migrate, or become extinct,” says Beck. This can already be seen, for example, in red foxes, oak trees, and polar bears, all of which are shifting their habitats—with polar bears having hardly any refuges left. The consequences of climate change are also becoming increasingly visible in agriculture.

Both southern Italy and Great Britain belong to the “temperate zone,” but feel very different. In order to describe the great diversity on the planet more accurately, Köppen and Geiger divided the five main classes into 30 climate zones. They took into account factors such as whether there is a dry or rainy season and how warm or cold it is in summer and winter.

Southern Italy and Great Britain are thus divided into different subzones: the warm mediterranean climate, where summers are hot and dry, and oceanic climate zone, where precipitation is evenly distributed throughout the year, as in England. These 30 subzones are also shifting rapidly, as can be seen in Germany.

At the beginning of the 20th century, most of what is now the Federal Republic of Germany still had a humid continental climate.

Between 1991 and 2020, practically only the southeast of the country still fits this type. More than two-thirds of the country's territory is now characterized by a temperate oceanic climate similar to that of Great Britain.

Apart from a few pockets on the edge of the Alps and in the low mountain ranges, there are likely to be hardly any places with a cold continental climate left by the end of the 21st century if the world continues on its current climate path.

This is now also accompanied by humid subtropical weather, similar to that found in the region around Venice and the Po Valley in Italy. In a few decades, this could also be the case in the Upper Rhine Plain, which is already the warmest region in Germany today.

East of the Harz Mountains, a semi-arid steppe climate could develop, similar to that found today in inland Spain.

This does not mean that cacti will soon be sprouting up around Berlin, as the search engine Ecosia claimed in an April Fool's joke. The composition of the soil, the nutrients it contains, and human influence also play a major role in vegetation, and plants tend to shift their habitats rather slowly. In addition, Köppen-Geiger maps do not accurately reflect extreme conditions such as droughts or cold spells, and they also fail to take into account factors such as sunshine duration and wind strength. Furthermore, future precipitation patterns are generally hard to predict.

Nevertheless, the Federal Environment Agency already sees clear winners and losers of climate change: evergreen trees such as cherry laurel and Chinese hemp palm are increasingly surviving German winters and are therefore spreading, as are many other plant and animal species.

Chinese windmill palm (Trachycarpus fortunei)

Most newly introduced species are harmless, but some have devastating effects. For example, the red swamp crayfish transmits “crayfish plague” to native crayfish species.

Red swamp crayfish (Procambarus clarkii)

The disease has led to the extinction of European crayfish in entire regions. The Asian tiger mosquito could transmit diseases to humans that have not yet spread in this country, while giant hogweed and ragweed (also known as ambrosia) are known to cause allergies. They all like warm temperatures.

The polar regions of the Earth are likely to shrink the most in the future. You don't have to travel to the poles to find such climate zones; they also exist in high mountains such as the Alps in the form of alpine permafrost. Here, the ground is permanently frozen.

In 1900, the „nival zone“, or eternal snow, began at an altitude of around 3,030 meters in the Alpine region.

Today, the permafrost boundary lies a good 200 meters higher, with the result that the permafrost belt has shrunk significantly.

At the same time, the tree line is rising. Pure coniferous forests now find suitable conditions at altitudes of up to 1,900 meters, an increase of 150 meters as a result of global warming.

By 2100, fir trees and other conifers are likely to grow at altitudes well above 2,100 meters unless global greenhouse gas emissions are reduced rapidly in the near future. Mixed forests and deciduous forests are advancing from below.

At the same time, permafrost is becoming more limited. According to an Austrian study, depending on the emissions scenario, the boundary of permafrost will be between 3,500 and 4,000 meters in 2100.

In the worst case scenario, only around 80 Alpine peaks would remain permanently covered with snow and ice. Today, the number is at more than 3,000.

Another hotspot for climate change is in Eastern Europe. “Olive trees are now being successfully cultivated in regions such as Austria and northeastern Croatia, which used to be too cold for them,” says Beck.

The country whose climate has changed the most worldwide since the beginning of the 20th century is Hungary.

As recently as 1900, the territory that is now Hungary had an exclusively continental climate, characterized by sharp temperature contrasts between summer and winter.

81 percent of the country's territory has now slipped into a temperate climate zone.

This is likely to change significantly again by 2100. If climate protection measures remain unchanged, Hungary will then mainly have a humid subtropical climate, similar to that of southern China today.

The past few months have already provided a foretaste of this future. In April, climate services pointed to an unusually strong anomaly in soil moisture across large parts of Eastern Europe.

Although Hungary has had sufficient rainfall, Poland, Belarus, and Ukraine have been far too dry since last summer. “The probability of a drought year in these regions is high,” warns the German Weather Service (DWD).

The fact that Eastern Europe is particularly affected by global warming is likely to have global implications. The region is one of the most productive for grain cultivation worldwide. Many countries in the Global South also depend on wheat imports from Europe to secure their food supply.

Especially since climate change is also disrupting agricultural conditions there, as can be seen in South Africa and the neighboring microstates of Lesotho and Eswatini. They are changing most rapidly in the southern hemisphere. Here you can see the climate zones from 1900 to 1930.

Since the beginning of the 20th century, 28 percent of its territory has shifted into a new climate zone. Hot deserts and hot steppes are spreading, limiting opportunities for agriculture.

By 2100, a further 44 percent of the combined territory of the three countries is likely to slip into new climate zones.

This is where the Köppen-Geiger system reaches its limits. Hot deserts are already the driest regions on Earth. In the future, such regions will often simply become even drier and hotter.

The impact such changes can have on people is evident in India, for example.

Even before climate change set in, it was a hot country. Between 1901 and 1930, tropical conditions prevailed in around one third of the country – meaning no month below 18 degrees Celsius, often accompanied by high humidity of more than 80 percent during the rainy season.

Throughout the 20th century, tropical areas grew by around 20 percent.

High temperatures combined with high humidity are particularly stressful for the human body. This is because the skin secretes sweat to cool itself down. The sweat evaporates, thereby carrying away excess heat.

However, if temperatures and humidity rise too high, this mechanism no longer works: the air becomes so saturated that it cannot absorb any more water, causing the body to overheat even at rest. At a wet bulb temperature of 28 degrees Celsius, humans can hardly cool themselves down by sweating.

As researchers from the Indian Institute of Science in Bangalore recently reported, the annual number of hours of “humid heat stress” in the city of Kolkata has increased sixfold since the 1940s. The coastal region in the northeast is particularly affected by these extreme conditions.

The problem is that there are hardly any countermeasures against humid heat, apart from air conditioning, which is of little use to field workers except during breaks.

And tropicalization continues: while areas with temperate climates are shrinking, tropical zones in India could expand by 65 percent by 2100. At the same time, these regions are becoming increasingly hotter.

According to a study by Columbia Climate School, this development is leading to increased heat stress in many regions of the world. In parts of Mexico and the Amazon, northern Colombia, along the Red Sea coast, in Southeast Asia, Malaysia, and Indonesia, people are already exposed to extremely stressful hot and humid conditions for at least three months of the year.

If the world remains on its current emissions path and the Earth warms by three degrees compared to pre-industrial times, it is feared that the productivity of harvest workers could plummet by 30 to 50 percent, resulting in rising food prices.

It's not just humans who will eventually find it too hot: crops such as corn and wheat also suffer when temperatures are too high. Wheat, for example, grows best between 10 and 25 degrees Celsius.

The coldest habitats on Earth outside Antarctica are found in northeastern Russia, Alaska, and northern Canada. In addition to low temperatures, especially in winter, they have something else in common: forests.

Boreal coniferous forest in the Yukon Territory, Canada.

From Norway to Kamchatka, from the Bering Strait to Labrador, a sea of dark green stretches practically uninterrupted from coast to coast. Every third tree in the world grows here.

Taiga, or “land of small sticks,” is the name given to the subarctic zone, shown here in its 1900 contours.

Since then, the subarctic climate zone has shrunk significantly. In the south, spruce, pine, and other conifers now compete with advancing deciduous trees.

According to a study recently published in the journal Geophysical Research Letters, boreal regions in Siberia and the barren tundra bordering the north are warming particularly rapidly.

In Alaska and central Canada, researchers used satellite data to identify more surface water and flooding than in the past, which they interpret as a sign of thawing permafrost.

This trend is likely to continue until 2100 if the world maintains its current level of climate protection. The subarctic climate zone of Eurasia will then probably be interrupted for the first time since the last ice age, and the evergreen belt will begin to crack.

This could exacerbate the global climate crisis. The permafrost in the north stores enormous amounts of carbon, which can be released in the form of carbon dioxide (CO₂) or methane when it warms up.

According to a team led by Anna Virkkala from the US research center Woodwell Climate, a third of the Arctic region has already been degraded into a source of greenhouse gases.

Although the region as a whole probably still absorbs more CO₂ than it releases due to its lush vegetation, more and more greenhouse gases are entering the atmosphere, mainly due to thawing permafrost and an increase in forest fires.

Forest fire in northern Quebec, Canada, in 2023

It is quite certain that not all countries will suffer equally from these massive changes. At the beginning of the 20th century, Iceland only had a temperate zone in the far south, while the interior of the country was polar and heavily glaciated.

Meanwhile, the temperate areas have expanded, and the glaciers in the interior of the country are retreating at an ever-increasing rate.

“Global warming has generally had a positive effect on agriculture: with warmer summers and a longer growing season, yields per acre are increasing,” according to the Icelandic Meteorological Office. Birch forests are also expanding.

This trend is likely to continue until 2100. If current climate protection measures remain in place, parts of Iceland are likely to experience warm summers for the first time, with average temperatures of more than ten degrees Celsius for at least four months. Not all Icelanders will necessarily view this as a negative development.

But even if climate targets are achieved, Iceland will gain temperate areas.

If, on the other hand, the world continues to rely heavily on fossil fuels such as oil, natural gas, and coal, and the temperature rises by around 3.5 degrees, Iceland could eventually look like this.

The polar regions that are typical today would be roughly halved in size, and entirely new communities of animals and plants would probably emerge on the coasts.

In this scenario, the face of the island would have changed fundamentally. This is what could happen globally—but it is by no means certain. “The corridor of action is wide open,” says meteorologist Peter Hoffmann from the Potsdam Institute for Climate Impact Research (PIK).

According to Hoffmann, the remeasurement of climate zones shows the wide range of future developments. Whether only five percent of land areas will move into a new climate class or up to 13 percent, which is as much as India and Pakistan combined: it is still up to humanity.

Climate Zones

Blurred Boundaries

Remember the colorful climate map in your school atlas? Global warming is currently redrawing it. A journey across the map to places that are changing faster than ever before.

Climate change does not always appear grim and gloomy. Sometimes it manifests itself in rich yellow, bright red, metallic blue—just like the bee-eater.