Climate change

Deadly heatwaves could make China’s key food production region unlivable, MIT study says

Such would be the intensity of the heat that healthy people would die after just six hours of exposure to it, scientists say

PUBLISHED : Wednesday, 01 August, 2018, 10:31pm
UPDATED : Thursday, 02 August, 2018, 7:09pm

A spike in the frequency of heatwaves as a result of climate change could make one of China’s main food growing regions the deadliest place on Earth before the end of the century, according to new research.

The massive North China Plain, which spans 14 million hectares (35 million acres) across five provinces, from Beijing in the north to Shanghai in the east, is currently home to about 400 million people.

But according to a study by scientists at the Massachusetts Institute of Technology in the United States, and published in the journal Nature Communications on Tuesday, the predicted heatwaves, caused by rising temperatures and increased humidity in the region, will make it almost uninhabitable.

“This spot is just going to be the hottest spot for deadly heatwaves in the future,” said Elfatih Eltahir, a hydrology and climate professor at MIT who led the research.

Such would be the intensity of the heat that healthy people could die after just hours of exposure to it, he said.

The potentially fatal problem is a measure known as the “wet bulb” temperature, the study said. When this reaches 35 degrees Celsius, the heat and humidity, even in the shade, are so intense that the body cannot cool itself. So even perfectly healthy individuals can die within six hours.

The “wet bulb” measure takes its name from the way scientists measure this type of heat by covering the bulb of a thermometer with a damp cloth.

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Although the North China Plain is a primary food production region – it generates 20 per cent of the country’s grains, according to the Chinese Academy of Sciences – it does not get a lot of rainfall. Farmers therefore rely on irrigation systems during the spring and early summer growing season to nurture their crops, Eltahir said.

While climate change was the main driver of the problem, “irrigation exacerbates the impact,” he said.

Such is the scale of irrigation use that it can add about 0.5 degrees to the high wet bulb temperatures.

This is because the evaporation of irrigation water leads to higher humidity and because water vapour is itself a powerful greenhouse gas.

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Despite the undoubted effect of irrigation, Beijing and the rest of the world must reduce their carbon emissions if disaster were to be averted, Eltahir said.

“China is currently the largest contributor to the emissions of greenhouse gases, with potentially serious implications to its own population,” he said.

“But global society, not only China, should take serious steps to mitigate climate change.”

China has already seen evidence of rising temperatures over the past half a century. The MIT study found the plain had experienced a significant increase in extreme heatwaves, including one in 2013 that lasted for 50 days and saw a 141-year temperature record in Shanghai smashed.

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Between 1951 and 2006, the mean surface temperature across China rose by about 1.35 degrees, a rate that was nearly twice the figure for the world as a whole, the study said.

The MIT research into the North China Plain was the third in a series of investigations into deadly heatwaves, with the previous two looking at the Persian Gulf and South Asia.

While both of those areas were found be at high risk, the threat level in China was the highest on Earth, the study said.