Extreme weather events like those that struck around the world this summer are resulting from human activity disturbing the enormous winds that circle the planet, according to a new study.
The record breaking heatwaves that struck from Japan to Algeria were seen by the climate change community as a sign of things to come, with many blaming conditions on steadily rising global temperatures.
Weather becomes more extreme when instead of moving on it stays in the same place for days or weeks on end. Never-ending rainfall causes flooding, and prolonged sunny weather sparks droughts and wildfires.
Evidence is now mounting to show that human-induced warming in the Arctic is distorting the planet’s natural circulation patterns such as the jet stream and making these “stalling” events more likely.
“While it might not sound so bad to have more prolonged sunny episodes in summer, this is in fact a major climate risk,” said Dr Dim Coumou from the Potsdam Institute for Climate Impact Research (PIK).
“We have rising temperatures due to human-caused global warming which intensifies heat waves and heavy rainfall, and on top of that we could get dynamical changes that make weather extremes even stronger – this is quite worrying.”
In a paper in the journal Nature Communications that brings together years of sometimes conflicting research on this complex phenomenon, Dr Coumou and his colleagues have laid out the process by which global warming “stalls” the weather.
It is well documented that global warming is happening faster in the Arctic than elsewhere, effectively reducing the temperature difference between the far north and the equator.
This is a problem, because this gradient drives the eastward movement of airstreams far above our heads, and as it weakens, blockages start to occur.
“The weather in a given region gets stuck,” explained PIK director Dr Hans Joachim Schellnhuber.
“Rains can grow into floods, sunny days into heat waves, and tinder-dry conditions into wildfires.”
Dr Simon Wang, a climate researcher at Utah State University who contributed to the work, said there is evidence for several factors that are increasingly stalling weather systems.
“Besides Arctic warming, there’s also the possibility of climate-change-induced shifting of the storm tracks, as well as changes in the tropical monsoons,” he said.
Dr Coumou said there was still much to understand about the link between climate change and extreme weather, but the evidence suggested greenhouse gas emissions are driving this phenomenon.
“While we do not have certainty, all in all the state of research indicates that changes in airstreams can, together with other factors, lead to a phenomenon that sounds funny but isn’t: extreme extremes,” said Dr Coumou
A further study carried out by Dr Coumou and colleagues found that the wildfire that struck Canada’s Alberta region in 2016 was preceded by stalling summer weather that increased the risk of fire.
Preliminary analysis by an international team revealed in July that this summer’s European heatwave was made twice as likely by climate change.
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