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Superpowers beware.聽More intense heatwaves are in store this century聽as a result of greenhouse gas emissions.

The grim news comes from two studies that model how climate change will affect heatwaves in the US and Russia.

Russia already has a heatwave problem. Its worst for 40 years struck in summer 2010.聽, compared with a seasonal average of 23掳C, and the heatwave lasted all of July and into mid-August. It resulted in the deaths of 55,000 people in western Russia 鈥� 14,000 in Moscow alone 鈥� and caused economic losses of $15聽billion, not least through the聽loss of 9 million hectares of crops.

Even worse is to come, says聽聽at the Royal Netherlands Meteorological Institute. He and his colleagues modelled the conditions that led to the heatwave, including a huge anticyclone that sat over Russia, locked in place because the usual聽jet stream of air flow has stalled. The team looked at how those same conditions would be affected by warmer temperatures.
If similar heatwaves occur this century, the team found that temperatures in Russia could be as much as 8.4掳C higher than they were in 2010.

One of the reasons for soaring temperature is a change in soil behaviour. Moist soils can absorb more heat than dry soils, reducing air temperature. But the team says the projected temperature rises would overwhelm this effect, even if spring rains were plentiful. 鈥淭his constraint will disappear in the future,鈥� they say.

The cooling effects of soil moisture will also diminish in the US, according to a second study.聽聽of the University of Miami in Florida and his colleagues modelled previous heat waves to see how natural variations in climate influenced them. Then they included the effects of climate change.

鈥淎ll regions will experience extreme temperatures of 5 to 10掳C above normal summer temperatures for the 21st century,鈥� says Lopez.

The models showed how long it聽would take for climate change to account for half of the extreme events and heatwaves in four regions of the US.

The first to reach the threshold, in about 2028, will be the Western US:聽a region already beset by drought. Next will be the Great Lakes in 2037, followed by the northern Great Plains in 2056 and the southern Great Plains in 2074. 鈥淭hese are the projected times when anthropogenic climate change will assume a dominant role in heatwaves, compared with natural variability,鈥� says Lopez.

The two plains regions will take longer to succumb, because they are watered by a wave of moisture from the Gulf of Mexico:聽. This boosts the soil moisture that makes heatwaves milder. But neither the Great Lakes nor the Western US have this luxury, so climate change will bring them heatwaves sooner.

This article appeared in print under the headline 鈥淓xtreme heat for US and Russia鈥�