Canicles, droughts, rains ... Already more intense and more frequent, extremes extreme summers of the northern hemisphere will also last longer, even with a global warming limited to + 2 ° C, according to a study published Monday . "Extreme weather events are usually analyzed in terms of intensity and frequency, but it is often their persistence that causes the most serious effects", including on human health and agriculture, says this study appeared in the Nature Climate Change magazine.
The probability of exceeding two weeks increases
Researchers have therefore looked into the risks of these periods of heatwaves or precipitation events, particularly in the temperate zones of the northern hemisphere. "If the world warms by + 2 ° C from pre-industrial levels, we could see a major change in summer weather conditions," commented Peter Pfleiderer of the Climate Analytics Research Center in a statement.
According to the study, in a world at + 2 ° C, the probability of heatwaves of more than two weeks should increase by 4% on average, with even greater risks in North Asia, the center of the Europe and eastern North America. The probability of persistence of both hot and dry periods is similar, but with large regional peaks, up to 20% in eastern North America. The risks of a seven-day period of significant rainfall increase by 26%, posing threats of flooding.
The signs are already there, the urgency too
"We can predict more and more significant impacts of extreme weather events during the summer, but our research shows that by limiting warming to + 1.5 ° C, as provided for in the Paris Climate Agreement, would reduce them considerably, "said Carl-Friedrich Schleussner of Climate Analytics in a statement. "Bearing in mind that with the current pace of reductions in emissions (of greenhouse gases), the world is moving towards + 3 ° C, our study underlines the urgent need for action", a- he added.
The 2015 Paris agreement aims to limit warming to + 2 ° C compared to the pre-industrial era, or even + 1.5 ° C. But the world has already warmed by + 1 ° C, already leading to an increase in heat waves, droughts or storms. And the signs of a longer persistence of these events are already there, notes the study.
For example, in 2018 Europe experienced a particularly long hot and dry period, from April to September, interrupted by brief periods of cooling and rain, leading in particular to a drop in wheat harvests in Germany of 15%, according to Researchers. And in the spring of 2016, three close periods of several consecutive days of rain had contributed to the overflow of the Seine in Paris.