Summer may become more severe

Scorching summer heatwaves and downpours are set to become more extreme in the northern hemisphere as global warming makes weather patterns linger longer in the same place, scientists said on Monday.

They said there was a risk of "extreme extremes" in North America, Europe and parts of Asia because manmade greenhouse gas emissions seemed to be disrupting high-altitude winds that blow eastwards in vast, looping "planetary waves".

"Summer weather is likely to become more persistent - more prolonged hot dry periods, possibly also more prolonged rainy periods," said Dim Coumou, lead author of the study at the Potsdam Institute for Climate Impact Research (PIK) and Vrije Universiteit Amsterdam.

"Both can lead to extremes" such as heat, drought, wildfires or flooding, he told Reuters of the findings in the journal Nature Communications, based on a review of existing scientific literature.

Many parts of the northern hemisphere have experienced baking heat this summer, with wildfires from California to Greece. Temperatures topped 30 Celsius even in the Arctic Circle in northern Europe. The stalling of weather patterns could threaten food production.

"Persistent hot and dry conditions in Western Europe, Russia and parts of the US threaten cereal yields in these breadbaskets," the authors wrote. They linked the slowdown in weather patterns to the Arctic, which is heating at more than twice the global average amid climate change.