Europe, North America and parts of Asia can expect both more intense and longer lasting periods of heat, drought and rain during summer as the planet warms, according to a new study. The changes could affect health, agriculture and ecosystems, the study suggests. The research, published this week in the journal Nature Climate Change, adds that limiting global warming to 1.5 degrees C above pre-industrial levels in line with the Paris Agreement would largely avoid such impacts.
Extreme weather of various kinds already appears to be increasing across the midlatitudes. The study is perhaps the first to quantify how the persistence of heat waves, drought and rainy summer periods would increase in the temperate zones of the northern hemisphere if global temperatures continue to rise. Models already project that as the world warms, the number of hot days will increase, so hot periods would be expected to get longer in general. However, the new research also looked to see whether days that are hotter than average in the new, warmer climate would cluster together. The study projects that they will, producing more severe heat waves in the future. It projects that periods of drought or extreme rainfall would cluster similarly.
“We could see a significant shift in summer weather conditions from the patterns we know today,” said lead author Peter Pfleiderer, a scientist at the nonprofit Climate Analytics and Humboldt University, both based in Berlin. “Extreme weather would become more persistent. Hot and dry periods, as well as consecutive days of heavy rain, would all get longer,” he said.
Study coauthor Kai Kornhuber, a postdoctoral researchers at Columbia University’s Lamont-Doherty Earth Observatory, said, “The longer extreme weather lasts, the more harm it brings.” As an example, he cited 2017’s Hurricane Harvey, which hovered over Texas for days, bringing record flooding and infrastructure damage. “Our study shows that specifically in the densely populated midlatitudes, we have to expect weather to become more persistent and longer lasting,” he added.
According to the study, if the world warms to 2 degrees C above pre-industrial levels, the chance of hot periods lasting longer than two weeks will increase by 4 percent, compared with today’s climate. But this change would be more pronounced in central Europe, northern Asia, and especially in eastern North America, where hot spells might become 20 percent more likely. Periods of hot and dry conditions lasting longer than two weeks would become 10 percent more likely in central North America. Periods of heavy rain would increase the most: 26 percent higher across the entire northern temperate zone, compared to today.
The study projects the effects to come in part from systematic weakening of large-scale summer atmospheric circulation, including movements of the Jet stream and storm tracks. As circulation slows down, hot and dry conditions will be able to build up over the continents. Rain-bringing cyclones will also be able to persist longer in one place.
The impacts of hot and dry extremes on health, ecosystems, agriculture and economy would grow significantly the longer these conditions persist, say the authors. Likewise, multiple consecutive days of heavy rain would exacerbate the risk of severe flooding. Recent record-breaking weather events across North America, Europe and northern Asia provide glimpses of how the persistence of such conditions can compound impacts. For instance, during the 2018 European heat wave, several spells of hot and dry weather, each lasting weeks, contributed to wheat yield losses of 15 percent in Germany. In the United States, the past 12 months have been the wettest on record, and the central agricultural states experienced weeks of continuous flooding and resulting crop losses.
“We can expect increasing impacts from extreme summer weather at higher levels of warming, but our research shows that limiting warming to 1.5 degrees C [would] reduce them considerably,” said study coauthor Carl-Friedrich Schleussner of Climate Analytics and Humboldt University. “Bearing in mind that the current slow pace of reducing emissions puts the world on track to 3 degrees C, our study underlines the need for urgent action. ”
This story was adapted from a press release by Climate Analytics.