Global Warming Causes Cropland Areas to Shrink
Wheat: minus 15 percent; corn: minus 6.6 percent; rice: minus 6.6 percent; potatoes: minus 14 percent. These numbers don’t refer to the latest price fluctuations in the commodity markets, but instead reveal how much the land available for growing these crops will decrease worldwide if the climate warms by two degrees. These figures were published last year in the journal Nature Food by a research team led by Sara Heikonen and Matti Kummu at Aalto University, which included UZH geographer Daniel Viviroli.
The researchers worked out the relevant percentages for the 30 most important food crops for four different climate scenarios.
They concluded that, if the climate warms by two degrees, the land available for growing will decline for 25 of the 30 crops.
“If warming rises above two degrees, a decline in cultivation area can be expected for all crop species,” says Sara Heikonen of Aalto University in Finland, who analyzed the data. “Staying below two degrees warming requires serious reduction in greenhouse gas emissions during this decade according to the IPCC.”
Gains in the North, losses in the South
In all the scenarios calculated by the team of researchers, there are also gains in arable land alongside the losses. These gains are primarily at medium and higher altitudes, such as in Europe. Changes in the climate at these altitudes will make it possible to grow crops that could not previously flourish because the temperatures were too cool.
In the mildest scenario with the climate warming by 1.5 degrees, such gains may offset the losses across the globe.
In the other scenarios, the declines will predominate.
If the climate warms by four degrees, the amount of land available for cultivating legumes, oilseeds and starchy root crops like potatoes, sweet potatoes, yams and cassava will decline by more than 50 percent. The new land available for cultivation will be no higher than 20 to 25 percent.
Particular impact on tropical and subtropical regions
“The impact of climate change on arable land is particularly acute in tropical and subtropical regions,” says Viviroli. A hydrologist by trade, he has compared the different climate scenarios by looking at levels of precipitation, temperatures and evaporation conditions.
Blue areas indicate current cropland
(Data: Heikonen, S. (2025)
Red areas indicate the decline in cropland. The darker the color, the greater the decline (25%–75%).
Use the slider to see the decline under different scenarios.
If the average global temperature rises by two degrees, 25 to 30 percent of today’s production in the belt extending south of the Sahara could be lost from the safe climatic space. This novel concept incorporates the three decisive factors for crop production (precipitation, temperature and aridity) and describes under which conditions a crop can be cultivated in a certain area.
North Africa and the Middle East are also severely affected.
In these regions, many crops are already growing at a temperature that is close to the limit of what they can tolerate.
Climate change will therefore affect areas that are already finding it a big struggle to produce a sufficient amount of food. “These are places where people rely very much on subsistence farming,” explains Viviroli. The losses can’t simply be offset by imports from other regions because the economy does not provide the opportunities for this.
Water shortage and dams
In addition to the increase in temperature, the declining level of precipitation in lowland regions is another reason why the amount of usable arable land is dwindling. Although a lack of rainfall can be partially compensated for with additional or more efficient irrigation, almost a billion people living in lowland regions such as the Ganges, Brahmaputra and Meghna river basins currently depend on receiving a supply of water from the mountains, as Viviroli has shown in another study. By the middle of the century, this figure is set to rise to 1.5 billion.
70 percent of the water that is taken from rivers, lakes or groundwater is used for irrigation in agriculture. With the onset of climate change, the capacity of mountain regions to store water for a longer period of time will also decrease.
If the glaciers recede and there is less snow on the ground, the supply of water from the mountains will also change. “The snowmelt currently coincides nicely with the vegetation seasons,” says Viviroli, “and this supports the growth of crops.”
If the snowmelt starts earlier in the year, this coincidence will no longer exist and the water would then need to be stored artificially in the mountains. This means constructing dams, for example. “They represent one possible strategy for adapting, but they come with many drawbacks,” explains Viviroli.
Aside from their negative ecological impacts, they require a large capital outlay and in certain regions may cause conflicts over who has access to water resources.
Orphan Crops as an alternative?
Another strategy is to switch to crops that are more resistant – for example, the marama bean, which grows in southern Africa.
The yellow area shows the approximate distribution range of the marama bean. Yellow dots indicate locations where the plant has been found. (Data: GBIF.org)
“This plant grows on extremely barren soils and can withstand great heat and arid conditions,” says the plant biologist Ueli Grossniklaus, who has teamed up with the University of Mpumalanga in South Africa to explore this in depth and, among other things, has decoded its genome.
You can eat the seeds of the bean, which are a bit like chestnuts, but about half the size. They provide a truly wonderful source of nutrients. “They contain more protein than soybeans, more fat than peanuts and more vitamins and trace elements than other foods.” In short, it performs better for almost all its ingredients than the best of the foods that are often consumed today.
The marama bean is what is known as an orphan crop, which is a food that has not previously been considered in breeding or cultivation. “It could already be grown today on land where nothing else will grow,” says Grossniklaus. But there are still many hurdles to overcome before it can be grown intensively because the marama bean combines a number of properties that would normally preclude breeding and domestication. The seeds do not germinate on their own, the plant does not fertilize itself and it does not flower regularly.
Breeding would be required to cultivate the bean for food production. “But at the moment we have no idea how to go about this,” says Grossniklaus. There’s just too little knowledge about the plant. Grossniklaus is one of the few scientists who is actually studying the marama bean. However, his collaborative project, which is funded by the Swiss National Science Foundation and the South African National Research Foundation, will soon be coming to an end. At the moment, there is no more funding available for further research or field trials.
Accelerating plant breeding
The example of the marama bean shows that, even if certain orphan crops would be capable of surviving under changed climatic conditions and providing a high-quality food source, there is still a long way to go before they can be utilized intensively. This will scarcely compensate for the losses of land that will occur in areas that have previously been cultivated.
“We’ll need to find a way to adapt vital crops like wheat, corn and rice more quickly,” says Grossniklaus. Although it’s true that conventional breeding could produce more resistant or higher-yielding varieties, this process is extremely laborious and takes too long. “By the time that traditional breeding produces a variety that is more able to withstand the effects of a warming climate, we may already have reached the tipping point for the climate,” says Grossniklaus.
We’ll need to find a way to adapt vital crops like wheat, corn and rice more quickly.
This is why various countries, such as the USA or China, are growing varieties that have been produced with the aid of genome editing. This involves using the CRISPR/Cas method to deliberately modify the genome of a plant. “If I know which gene is relevant for a plant’s ability to tolerate drought, I can use this method to modify it,” explains Grossniklaus. “This is more efficient than years of breeding with trial and error.”
Diversity increases yields
In contrast to conventional genetic engineering, genome editing of the plant does not involve the introduction of any foreign genes, with only the plant’s own genome being modified. “These are changes that also occur naturally or in mutation breeding, which is commonplace today,” says the plant geneticist. In Switzerland, genome-edited plants are treated the same as genetically modified plants and their cultivation is prohibited. But the consequences of climate change could perhaps lead to a rethink in this area. “In places where there is a great need to adapt, transgenic plants are being allowed, for example black-eyed peas that are resistant to the bean pod borer in Nigeria,” states Grossniklaus.
One issue when it comes to breeding resistant or higher-yielding crops is that the gene pool of the varieties grown today is very small. This means there is no great diversity within a plant species. But diversity is beneficial: if different variants of a species are grown in a field, they will produce a greater yield. UZH professor of environmental science Bernhard Schmid is one of the academics to have discovered this in his research.
This effect is also seen if the plants are genetically identical, but have a different epigenetic expression. This means that what makes the plants different is not their genes, but whether certain genes are active or not. Epigenetics enables plants to have different characteristics despite being genetically identical.
Grossniklaus recently revealed in a groundbreaking study that epigenetic characteristics can be inherited and selected, at least in part. This would make it possible to breed plant varieties that are epigenetically different. “By doing this, you could slightly increase the level of variation within the narrow gene pool of these crops,” says Grossniklaus. In tests conducted in a laboratory, Grossniklaus was able to show that these epigenetically different plants do actually produce a greater yield and are also more robust.
Climate protection is key
Given the impact that climate change is having on the land available for growing crops, it’s clear to Daniel Viviroli that agriculture needs to become more efficient and adaptable in all areas to enable it to provide a reliable food supply to the world’s population, which continues to grow. The study concludes that, even in the mildest scenario in which the climate warms by just 1.5 degrees, the losses of individual plant species or in individual regions will be substantial. Any warming beyond this will lead to significantly higher risks and losses.
Lots of strategies for adapting are costly, produce negative ecological impacts or are controversial for society. Even though it’s inevitable that we’ll need to adapt, Viviroli believes that climate protection providers the most important lever: “It’s absolutely key. Every tenth of a degree will have an impact.”