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Unchecked Warming Would Cut U.S. Grain Yields 20-50% by 2100


Without immediate greenhouse gas reductions, rising temperatures could drive United States grain yields down 20 to 50% by century’s end, leading to higher food prices and serious difficulties for developing countries, according to a new study this month in the journal Nature Communications.

The results show that “nowhere on Earth, not even a country as powerful as the U.S., can expect to ride out the climate storm that is brewing,” Climate News Network reports.

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“Wheat, maize (known also as corn), and soya are all likely to suffer substantial damage by the end of the century,” CN Net explains. “And while increased irrigation could help to protect them against the growing heat, that will be an option only in regions with enough water.”

While “the effects of a warming atmosphere will extend far beyond the U.S.,” the impact on one of the world’s biggest food exporters would mean that “world market crop prices may increase, causing problems for poor countries.”

Since irrigation would be insufficient to stem the losses in water-short regions, the research team led by Bernard Schauberger at Germany’s Potsdam Institute for Climate Impact Research pointed to greenhouse gas reductions as the only available solution.

The team compiled what they say was an unprecedentedly comprehensive set of computer simulations of U.S. crop yields,” writes CN Net correspondent Alex Kirby. “For every single day the temperature remains above 30°C, they find, maize and soya plants can lose about 5% of their harvest. But that is only the start. The simulations performed in the study show how quite small heat increases beyond this threshold can result in ‘abrupt and substantial yield losses.’”

Without “efficient” action to slash emissions, “harvest losses from higher temperatures of 20% for wheat, 40% for soya and almost 50% for maize can be expected by the end of this century. Extremely high temperatures, above 36°C, are expected to lower yields still further.”

The Washington Post notes that climate impacts on agriculture have been “a tricky research area—plants can react to the changing climate in a lot of complicated and even contradictory ways, and their responses may differ from one region and one crop to the next. In cold climates for instance, warmer temperatures might be a boon for plant life—research has already revealed a greening effect in certain northern regions of the world. In other places, hotter growing seasons could be devastating.

And, of course, climate deniers have claimed that rising atmospheric CO2 levels will actually be good for crops.

But those who question the consequences of climate change may have some reconsidering to do,” the Post reports. The Potsdam report “indicates that high temperatures can have significant damaging impacts on crop yields—and while access to more water can do a good job of mitigating these effects, extra carbon dioxide may not be all that helpful after all.”

Schauberger explained the basic dynamic in the Washington Post article.

“When temperature increases, the atmosphere demands more water,” he said, so evaporation from plants and soils increases.

That leaves plants short of water, at which point “they initiate a series of processes designed to help them survive—these may include closing the pores on the undersides of their leaves to prevent excess water loss,” writes the Post’s Chelsea Harvey. “Since these pores are also responsible for gas exchange, this process also forces plants to take in less carbon dioxide, which can affect their ability to photosynthesize. Water-stressed plants may also devote more of their energy to spreading roots underground and less to growing body mass above ground. All of these processes can reduce their yield in crops.”