Last summer’s unprecedented droughts, heat waves, wildfires, and flooding events in the northern hemisphere have been linked to atmospheric conditions resulting from a rapidly warming Arctic. With continued global warming the conditions that spawn such destructive and prolonged weather extremes will increase 50 percent on average and may increase as much as 300 percent, a new study in the journal Science Advances has revealed.
The wildfires in California and the heat wave in Europe were the worst ever. The unprecedented wildfires in the Arctic and flooding in Japan are also all connected to a slower jet stream that locks weather systems into place, says climate scientist Michael Mann from Pennsylvania State University, lead author of the study.
It’s not just last summer. The 2011 Texas/Oklahoma droughts, the 2013 European floods, the 2015 California wildfires, and the 2016 Alberta wildfires have been linked to a hotter Arctic that’s disrupting the flow of the jet stream.
“We’re seeing the impacts of climate change play out in realtime on our TV screens and in our news headlines,” Mann said.
People walk on a catwalk in a flooded St. Mark's Square during a period of seasonal high water in Venice, Italy, on October 29, 2018.
These events will be more frequent and more intense with continued burning of fossil fuels, he said. “Things could get a whole lot worse without immediate action to reduce carbon emissions.”
This study comes out the same time as new research published in Nature that suggests the world's ocean has been soaking up more heat than previously thought in recent years. The implication is that this could mean the planet is headed for even more rapid warming in response to greenhouse gas emissions, which in turn could further impact weather.
A river of air
The high-altitude, west-to-east winds known as the jet stream are driven by the temperature difference between the icy air of the Arctic and hot air from the tropics. The Arctic is warming two to three times faster than anywhere else, which reduces the temperature difference and slows the jet stream. Like a slow-moving river, a slower jet stream also meanders and can stall during the summer, sometimes for weeks.
The climate model projections about how often the jet stream will stall and lead to extreme events from now until 2100 range from a slight decrease to a 300 percent increase, said co-author Kai Kornhuber, a researcher at the Potsdam-Institute for Climate Impact Research in Germany. There isn’t enough good long-term data—and the various climate models handle the complexities of future cloud cover and tiny particles called aerosols from air pollution differently—Kornhuber said in an interview.
“However, a 50 percent increase is very likely and that’s likely conservative,” he said.
Coal’s big role
Shutting down coal-fired power plants will minimize the odds of summers like 2018 in the future, the study also shows. Coal plants are a major source of carbon dioxide (CO2) that traps the suns’ heat. They are also a significant source of air pollution in the form of small particles or aerosols that reflect some of the suns’ heat, causing regional cooling.
“A reduction of air pollution in the industrialized countries could actually restore some of the natural temperature difference between the mid-latitudes and the Arctic,” says co-author Stefan Rahmstorf, a climate scientist at the Potsdam-Institute for Climate Impact Research.
And that would help to prevent the future increase in stalling of the jet stream and the related weather extremes. “If we want to limit the increase of dangerous weather extremes, phasing out coal fast seems like a pretty good idea,” Rahmstorf said in a press release.