Cutting aerosol pollution may lessen extreme weather even with warming

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By Michael Le Page

Here’s yet another good reason to reduce aerosol pollution from fossil fuels: it could help limit the alarming increase in extreme weather around the world, such as severe flooding. But it’s far from a “get out of jail free” card: the reductions could trigger worse heatwaves and hurricanes in some places.

The world’s weather is growing increasingly extreme due to climate change. Warming-driven changes in the high-speed winds known as the jet stream appear to be contributing to recent summer extremes, from the record-breaking wildfires in Greenland last year to the unprecedented flooding in Japan this June and July, in which 225 people died.

“What these events had in common was a very unusual jet stream pattern,” says Michael Mann of Penn State University.

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His team has previously shown that as the temperature difference between the Arctic and mid-latitudes decreases, due to the rapid warming in the Arctic, the polar jet stream is becoming more likely to develop big latitudinal waves, or meanders, as it circles the globe. What’s more, these meanders can get stuck in place due to what the team call “quasi-resonant amplification” events, or QRAs.

Stuck weather

Stuck weather patterns can lead to serious weather extremes. “If the same weather persists for weeks on end in one region, then sunny days can turn into a serious heat wave and drought, and lasting rains can lead to flooding,” said team member Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany.

The team have now used climate models to look at how the number of QRAs will change as warming continues over the next century. Most models suggest that it will increase, and could even triple.

But if countries like China and India succeed in reducing harmful air pollution from coal burning, there will be no increase in QRAs. The reason is that sulphur aerosols, while bad for our health, have a regional cooling effect. If they are removed and the mid-latitudes warm more, the temperature difference between the Artic and the mid-latitudes will stop decreasing.

But that mid-latitude warming could of course have some undesirable consequences, from worsening heatwaves to making tropical storms even stronger.

“At this point there are certainly trade-offs when it comes to managing the increasing risk of extreme weather events,” says Mann. Cutting greenhouse gas emissions in addition to reducing aerosol pollution remains crucial, he says.

Journal reference: Science Advances, DOI: 10.1126/sciadv.aat3272