Global Warming Will Sear Three of Four Major Grain Crops, Says New Meta-study

Maize and wheat especially vulnerable, rice will hurt and only soybeans seem relatively impervious to rising temperatures

Rising temperatures will decimate food crops, say scientists: Picture shows desiccated ear of corn in Indiana, U.S. September 6, 2016.
Rising temperatures will decimate food crops, say scientists Jim Young, Reuters

Three of the four major grains on which the growing world population depends are vulnerable to global warming, says a new meta-analysis based on more than 70 studies.

Farmers have probably known that plants have optimal ranges in which they grow best since planting the first wheat some 23,000 years ago. Now science has proved the point.

The four crops on which humankind depends most are wheat, rice, maize, and soybeans. These are responsible for two-thirds of human caloric intake, says the team.

The starting point of the meta study was that the effect of climate change on these crop yields was not certain. Now they are. "Temperature increase reduces global yields of major crops in four independent estimates," the scientists state in the title of their paper title. At least soybean turns out to be relatively resilient to warmer temperature, within limits.

One degree change, 7% drop in crop

The sheer multiplicity of parameters make climate change prediction extremely difficult, but, as the team points out, understanding temperature and other impacts of the change is critical to future food security. Especially as scientists now agree that keeping median global warming less than 2 degrees Celsius will be almost impossible.

The meta-analysis by Chuang Zhao, Senthold Asseng of the University of Florida and others encompassed studies based on multiple analytical methods, including modeling global and local crop yields in response to temperature changes; statistical regression models based on historical weather and yield data; and artificial field warming experiments.

All methods indicate that rising temperatures are likely to hurt the global yields of wheat, rice, and maize, and significantly so – though, the team qualifies, specific results were highly heterogeneous across crops and geographical areas, and there were also some positive impact estimates.

A local miller pouring maize into his grinding mill, in the Kibera slums of Nairobi, Kenya August 6, 2017. Maize is particularly vulnerable to rising temperatures.
Thomas Mukoya, Reuters

Each 1-degree Celsius increase in global mean temperature is projected to reduce average global yields of wheat by 6%, rice by 3.2%, and maize by 7.4%, the team estimates, assuming no corrective methods, such as farming adaptations or genetic crop modifications to make them more resilient.

Soybean yields were hardier. How temperatures affected soy yields varied widely across crops and geographical areas, the team said: in some places, yields increased.

Their conclusion: the world needs to develop crop- and region-specific adaptation strategies to ensure food security for an increasing world population.

Rice is produced almost entirely in Asia, but corn for instance, a staple in the West, is grown around the world – which should be an advantage, for humankind. But part of the problem is that multiple areas on which the world depends are increasingly likely to get hit at the same time.

For instance, drought in the U.S. and China at the same time, which is now entirely feasible, could decimate the global corn supply: "Our simulations indicate that that type of scenario is possible in the current climate," researcher Chris Kent told Bloomberg. Just last month, China admitted that its north is suffering the worst drought in its history and that crops are suffering. Beijing, at least, is not in climate change denial.