Harvests In The US To Suffer From Climate Change

Some of the most important crops risk substantial damage from rising temperatures. To better assess how climate change caused by human greenhouse gas emissions will likely impact wheat, maize and soybean, an international team of scientists now ran an unprecedentedly comprehensive set of computer simulations of US crop yields. The simulations were shown to reproduce the observed strong reduction in past crop yields induced by high temperatures, thereby confirming that they capture one main mechanism for future projections. Importantly, the scientists find that increased irrigation can help to reduce the negative effects of global warming on crops - but this is possible only in regions where sufficient water is available. Eventually limiting global warming is needed to keep crop losses in check.

 

"We know from observations that high temperatures can harm crops, but now we have a much better understanding of the processes," says Bernhard Schauberger from the Potsdam Institute for Climate Impact Research, lead author of the study. "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 compare the model results to data from actual observations. This way, they can find out if they include the critical factors into their calculations, from temperature to CO2, from irrigation to fertilization.

 

Without efficient emission reductions, yield losses of 20 percent for wheat are possible by 2100

 

For every single day above 30°C, maize and soybean plants can lose about 5 percent of their harvest. The simulations have shown that the models capture how rather small heat increases beyond this threshold can result in abrupt and substantial yield losses. Such temperatures will be more frequent under unabated climate change and can severely harm agricultural productivity. Harvest losses from elevated temperatures of 20 percent for wheat, 40 percent for soybean and almost 50 percent for maize, relative to non-elevated temperatures, can be expected at the end of our century without efficient emission reductions. These losses do not even consider extremely high temperatures above 36°C, which are expected to lower yields further.

 

The effects go far beyond the US, one of the largest crop exporters: world market crop prices might increase, which is an issue for food security in poor countries.

 

 

"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," says co-author Joshua Elliott from the University of Chicago. When water supply from the soil to the plant decreases, the small openings in the leaves gradually close to prevent water loss. They thereby preclude the diffusion of CO2 into the cells, which is an essential building material for the plants. Additionally, crops respond to water stress by increasing root growth at the expense of above-ground biomass and, eventually, yields. "Irrigation therefore could be an important means of adaptation to dampen the most severe effects of warming," says Elliott. "However, this is of course limited by the lack of water resources in some regions."