Computer simulations predict a strong increase of events in which the undulations of the jet stream in the atmosphere stop moving along and grow very large. This can favor more frequent extreme weather events on the ground: the westerly winds stop pushing forward weather systems which hence become more persistent – a few sunny days grow into heatwaves, extended rains lead to floods. An international team of scientists links this to human-caused warming specifically in the Arctic.
Michael Mann from the Pennsylvania State University, lead author of the study to be published in Science Advances, says,
”We expect a roughly 50 percent increase in the incidence of atmospheric conditions that favor a slow, broadly meandering jet stream and stalled weather extremes… what it means is rather simple: people will likely experience extreme and potentially dangerous weather events more often.”
Professor Michael Mann Talking To CarbonTracker CEO, Anthony Hobley in the Arctic - Read More
These extremes have now been linked to a multitude of extreme impacts that have cost lives, livelihoods, ecological destruction and, of course, billions of dollars. The trouble is that humanity is not responding. In fact, we appear to be going in the wrong direction, despite the cost of renewable low-carbon energy sources falling in price. If there is any misunderstanding of what is driving these changes in the frequency of climatic extremes, this study shines a clear light. Stefan Rahmstorf from the Potsdam-Institute for Climate Impact Research (PIK), a co-author of the study says:
“Our analysis clearly shows, that there seem to be two crucial factors determining the frequency of these events."
Arctic warming and air pollution
Computer simulations that take into account the fact that the Arctic is warming much faster than the rest of the planet show a more pronounced increase of the stalling events. The same is true for simulations that include the effects of air pollution with tiny particles, so-called aerosols. Strong Arctic warming reduces the temperature difference between the North Pole and the subtropics, and it is this difference that is a major driver of the jet stream – hence the relevance of the Arctic. Air pollution blocks a part of the sunshine for instance in regions with lots of dirty coal-fired power plants and thus results in slight temporary local cooling. This also reduces the temperature difference to the North Pole.
"So one implication of our findings is that a reduction of air pollution in the industrialized countries could actually restore some of the natural temperature difference between the mid-latitudes and the Arctic – which in turn would help to prevent the future increase in stalling of planetary waves and the related weather extremes", says Stefan Rahmstorf. "It is interesting that closing down coal-fired power stations helps to avoid climate destabilization in two ways: by reducing greenhouse gas emissions that drive global and Arctic warming, and also by reducing air pollution. Thus, if we want to limit the increase of dangerous weather extremes, phasing out coal fast seems like a pretty good idea."
Saving the Arctic
It is clear now that the Arctic sea ice is disappearing at an increasing rate and that this is impacting the movement of the jet stream, which in turn is destabilising and increasing extremes in our weather.
As the warming trend continues unabated, humanity must stop during fossil fuels. In addition, we must look at ways of stopping and then reversing the heating trend. If we don’t then the outlook for civilisation, this century, looks bleaker by the day.
Article: Michael E. Mann, Stefan Rahmstorf, Kai Kornhuber, Byron A. Steinman, Sonya K. Miller, Stefan Petri, Dim Coumou (2018): Projected changes in persistent extreme summer weather events: The role of quasi-resonant amplification. Science Advances, Vol. 4, no. 10 [DOI: 10.1126/sciadv.aat3272] :http://advances.sciencemag.org/content/4/10/eaat3272
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