New research from the Potsdam Institute in Germany has added to concerns that rising global temperatures are set to damage the world’s most important staple crops.  

2016 was the warmest year in recorded history; in fact each of the last three years have broken temperature records, and each year from 2000-2016 is amongst the 17 warmest years on record, with only 1998 making the list from before the millennium.

Scientists from the specialist climate research institute at Potsdam looked at computer models of US yields three crops (wheat, maize and soybean). Their simulations - which researchers said were unprecedentedly comprehensive - showed a strong reduction in yields associated with higher temperatures from climate change, as predicted in previous work.

The researchers said that increased irrigation can help reduce the negative effects of global warming on crops, but this is possible only in regions where enough water is available. If more water is diverted to agriculture, it would engender major struggles over resources, as most major groundwater sources beneath the world’s breadbasket regions are being used faster than they can recharge, and agriculture already accounts of 70% of fresh water use worldwide (though this figure hides massive variation between regions).

They therefore said efforts to tackle global warming are in fact needed to keep losses in check.

Discussing the work, Potsdam researcher Bernhard Schauberger said, ”We know from observations that high temperatures can harm crops, but now we have a much better understanding of the processes. The computer simulations that we do are based on robust knowledge from physics, chemistry, biology; on a lot of data and elaborate algorithms. But they of course cannot represent the entire complexity of the crop system, hence we call them models. In our study they have passed a critical test."

The scientists compared the model results to data from actual observations, to find out whether anything was missing from their calculations (be it temperature, CO2 levels or irrigation).

For every single day above 30°C, maize and soybean plants can lose about 5 percent of their harvest. Without efficient emission reductions, yield losses of 20 percent for wheat are possible by 2100, researchers said, with losses of 40% for soybeans and 50% for maize predicted over the same period. They said theirs was a conservative estimate that didn’t take extreme heatwaves into account, though these could reduce yields further.

Joshua Elliott, from the University of Chicago, who also worked on the study, said, "The losses got substantially reduced when we increased irrigation of fields in the simulation, so water stress resulting from temperature increase seems to be a bigger factor than the heat itself.”

When water supply from the soil to the plant decreases, small openings in plants’ leaves gradually close to prevent water loss. In doing this, they stop CO2 being distributed in plants’ cells. Crops also respond to water stress by increasing root growth at the expense of above-ground growth which has an impact for yield. "Irrigation therefore could be an important means of adaptation to dampen the most severe effects of warming," said Elliott. "However, this is of course limited by the lack of water resources in some regions."