Global warming’s effect on jet stream could mean longer periods of extreme weather

A given weather pattern, whatever it may be, may persist for longer, thus driving extreme droughts, heat waves, downpours and more.

Since 2012, scientists have been debating a complex and frankly explosive idea about how a warming planet will alter our weather, one that, if it’s correct, would have profound implications across the Northern Hemisphere and especially in its middle latitudes, where hundreds of millions of people live.

The idea is that climate change doesn’t merely increase the overall likelihood of heat waves, say, or the volume of rainfall; it also changes the flow of weather itself. By altering massive planet-scale air patterns like the jet stream, which flows in waves from west to east in the Northern Hemisphere, a warming planet causes our weather to become more stuck in place. This means that a given weather pattern, whatever it may be, may persist for longer, thus driving extreme droughts, heat waves, downpours and more.

This basic idea has sparked half a decade of criticism and debate and, at the cutting edge of research, scientists continue to grapple with it. Now, a new study once again reinforces one of its core aspects.

Publishing in Nature Scientific Reports, Michael Mann of Pennsylvania State University and a group of colleagues at research institutes in the United States, Germany and the Netherlands find that at least in the spring and summer, the large scale flow of the atmosphere is indeed changing in such a way as to cause weather to get stuck more often.

The study, its authors write, “adds to the weight of evidence for a human influence on the occurrence of devastating events such as the 2003 European heat wave, the 2010 Pakistan flood and Russian heat wave, the 2011 Texas heat wave and recent floods in Europe.”

But what does it mean for global warming to alter the jet stream?

The Northern Hemisphere jet stream flows in a wavy pattern from west to east, driven by the rotation of the Earth and the difference in temperature between the equator and the North Pole. The flow is stronger when that temperature difference is large.

But when the Arctic warms up faster than the equator does, which is part of the fundamental definition of global warming and which is already happening, the jet stream’s flow can become weakened and elongated. That’s when you can get the resultant weather extremes.

“It’s sort of like if you confine an electromagnetic wave to a coaxial cable, then you’re not losing energy, it’s being tightly contained in that cable and sent to your television,” Mann said. “These waves aren’t losing energy, so they grow and get larger and get stuck in place as well.”

What the new study is saying is that in summer, in particular, this can occur. Moreover, it finds that a particular temperature pattern is linked to that behaviour and this temperature pattern, featuring an extra warm Arctic, is becoming more frequent over time, based on both observations and also a review of the outputs of high-powered climate change models that the researchers conducted.

https://www.thestar.com/news/world/2017/03/27/global-warmings-affect-on-jet-stream-could-mean-longer-periods-of-extreme-weather.html