Heatwaves longer, more deadly even in a 2C world

PARIS: Northern hemisphere summers will deliver dangerously longer heatwaves, droughts and bouts of rain even if humanity manages to cap global warming at two degrees Celsius, scientists said Monday.

With one degree of warming since pre-industrial times so far, extreme weather of this kind has already become more intense, with a single heatwave in 2003 leading to 70,000 excess deaths in Europe alone.

But the new study, published in the journal Nature Climate Change, is the first to quantify how much longer such events are likely to last if temperatures rise another degree. "We could see a significant shift in summer weather conditions," said lead author Peter Pfleiderer, a doctoral researcher at Humboldt University in Berlin.

"Extreme weather would become more persistent, hot and dry periods, as well as consecutive days of heavy rain would all get longer." Even small increases in the duration of extreme weather events can have devastating impacts on human health, food production, biodiversity and even economic growth.

During the 2018 heatwave in Europe, for example, several hot and dry spells, each lasting weeks, led to wheat yield losses of 15 percent in Germany. In the United States, the past 12 months have been the wettest on record, with large swathes of the heartland immobilised by continuous rainfall and flooding. The study looked at the changes in the northern hemisphere climate system that might be driving more extreme weather.

"The climate models show a systematic weakening of the large-scale summer atmospheric circulation -- including the Jetstream and storm tracks -- as the planet warms," said co-author Dim Coumou, a researcher at Vrije University Amsterdam.

"The increase in weather persistence can be linked to a weakening of this circulation." As it slows down, hot and dry conditions can build up over the continents. At the same time, water-bearing hurricanes and typhoons can persist longer in one place.

According to the new findings, the chance of hot periods lasting longer than two weeks in a 2C world will go up by four percent compared to today, with even larger increases in eastern North America, central Europe and northern Asia. Drought-like conditions of more than 14 days will become 10 percent more likely in central North America.

And bouts of sustained heavy rain will jump by more than a quarter across the entire northern temperate zone. All of these impacts would come on top of more intense droughts, diluvian rains and heatwaves, such as the record-setting temperatures that scorched much of the northern hemisphere in June and July of this year.