By studying the measurement data, the researchers realised that such large-scale heatwaves first appeared in the northern hemisphere in 2010, then in 2012, and again in 2018. Prior to 2010, however, the researchers did not find any instances of such large areas being affected simultaneously by heat.

Widespread heat extremes ever more likely

Model calculations confirm this trend. As the earth grows warmer, widespread heat extremes become more and more likely. According to model projections, every degree of global warming will cause the area of land in key agricultural regions or densely populated areas in the Northern Hemisphere that is simultaneously affected by extreme heat to grow by 16 percent. Should global temperatures rise to 1.5 degrees Celsius above pre-industrial levels, then one-quarter of the northern hemisphere will experience a summer as hot as the summer of 2018 every two out of three years If global warming reaches 2 degrees, the probability of such a period of extreme heat rises to almost 100 percent. In other words, every year extreme heat will affect an area just as large as the 2018 heatwave did.

“Without the climate change that can be explained by human activity, we wouldn’t have such a large area being simultaneously affected by heat as we did in 2018,” says Vogel. She is alarmed by the prospect of extreme heat hitting an area as large as it did in 2018 every year if global temperatures rise by 2 degrees: “If in future more and more key agricultural regions and densely populated areas are affected by simultaneous heatwaves, this would have severe consequences.”

Heat puts food security in jeopardy

Professor Seneviratne adds, “If multiple countries are affected by such natural disasters at the same time, they have no way to help one another.” This was illustrated in 2018 by the forest fires in Sweden: at that time, several countries were able to help with firefighting infrastructure. However, if many countries are battling major fires at the same time, they can no longer support other affected countries.

The food supply situation could also become critical: if broad expanses of areas vital to agriculture are struck by a heatwave, harvests could suffer massive losses and food prices would skyrocket. Anyone thinking these assumptions are overly pessimistic would do well to recall the heatwave that swept across Russia and Ukraine in 2010: Russia completely stopped all its wheat exports, which drove up the price of wheat on the global market. In Pakistan, one of the biggest importers of Russian wheat, the price of wheat rose by 16 percent. And because the Pakistani government cut food subsidies at the same time, poverty increased by 1.6 percent, according to a report by aid organisation Oxfam.

“Such incidents cannot be resolved by individual countries acting on their own. Ultimately, extreme events affecting large areas of the planet could threaten the food supply elsewhere, even in Switzerland,” Seneviratne emphasises.

She continued by pointing out that climate change won’t stabilise if we don’t try harder. At present, we are on course for a temperature increase of 3 degrees. The Paris Agreement aims for a maximum of 1.5 degrees. “We are already clearly feeling the effects just from the one degree that the global average temperature has risen since the pre-industrial era,” says Seneviratne.