By 2100, if global emissions rise at ‘business as usual’ levels, the world will see twice as many days with temperatures above 30 degrees Celsius (86 degrees Fahrenheit) as it does now, an international team of scientists wrote in the journal, Nature Communications.

Because crop yields start to drop when temperatures rise above 30 degrees Celsius, that suggests US wheat yields would fall by 20 percent, maize by 50 percent and soybeans by 40 percent by the turn of the century, the scientists found through computer modelling.

"If the U.S. has a problem with its yields then world market prices may rise, because the U.S. is such a huge exporter," said co-author of the study, Bernhard Schauberger. He added that the same crops in other parts of the world are likely to be similarly affected.

Irrigation may help protect yields, softening the water stress that causes plants to grow more roots and cut back on producing grain above ground.

Plants also close openings in the leaves to prevent water loss, which reduces their intake of carbon dioxide - an essential building material for the crops. More irrigation could help prevent that happening, the scientists said.

"Irrigation therefore could be an important means of adaptation to dampen the most severe effects of warming," said co-author, Joshua, Elliott from the University of Chicago. "However, this is of course limited by the lack of water resources in some regions."

Ultimately, the best way to protect crop yields is to curb greenhouse gas emissions, as agreed under the Paris Agreement on climate change, and hold global warming to ‘well below’ 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times, the scientists said.

The agreement, which came into force in November, seeks to phase out most greenhouse gas emissions by the second half of the century.

Source: Reporting by Alex Whiting, editing by Laurie Goering of the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, climate change, resilience, women's rights, trafficking and property rights. Visit: http://news.trust.org/climate