Nice sunny days can grow into heat waves -- and wildfires: summer weather is stalling

https://www.sciencedaily.com/releases/2018/08/180820085248.htm

"While it might not sound so bad to have more prolonged sunny episodes in summer, this is in fact a major climate risk," says Dim Coumou from the Potsdam Institute for Climate Impact Research (PIK) and Vrije Universiteit Amsterdam, lead-author of the review paper and co-author of the wildfire case study. "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." This summer is an impressive example of how stalling weather can impact societies: persistent hot and dry conditions in Western Europe, Russia and parts of the US threaten cereal yields in these breadbaskets.

Tons of studies have appeared on this topic in recent years, sometimes with seemingly conflicting results. For the paper now published in Nature Communications, an international team of scientists set out to review the existing research and tried to connect the dots, with a focus on the Arctic factor. Under global warming, the Arctic warms more than the rest of the Northern hemisphere. This reduces the temperature difference between the North Pole and the equator, yet this very difference is a main driving force for the airstreams. "There are many studies now, and they point to a number of factors that could contribute to increased airstream stalling in the mid-latitudes -- 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," says Simon Wang from Utah State University in the US, a co-author of the review paper.