Climate change and atmospheric dynamics reveal future extreme weather events

Climate change and atmospheric dynamics reveal future extreme weather events

From late June to mid-July 2021, the Pacific Northwest experienced an unprecedented heat wave, shattering temperature records and igniting a wave of concern about extreme weather events. As cities like Portland and Seattle, known for their mild summers, grappled with extremely high temperatures, scientists looked into why and how these meteorological anomalies occur.

Now, a collaborative team of researchers led by Michael Mann of the University of Pennsylvania’s College of Arts and Sciences has peeled back layers of atmospheric dynamics to reveal a startling truth: The interaction between natural systems and human-induced climate change sets the stage for climate change. More frequent and intense weather events.

“Our study shows that anomalous summer jet stream behavior — which we know is favored by human-caused global warming but is not well captured by current-generation climate models — contributed to the unprecedented ‘heat dome’ event in the Pacific Northwest for 2017,” says Mann. 2021″. Presidential Distinguished Professor and co-author of the paper published in Proceedings of the National Academy of Sciences.

The researchers found that before the heat dome event, planetary wave — large-scale atmospheric flows in the winds that cause weather change — amplified over the Pacific Northwest due to resonance, a related process where certain weather conditions coincide in some way. Which enhances the strength and stability of the wave.

The increase in wave amplitude will likely lead to a decrease in soil moisture in the area. Drier soils, in turn, contributed to increased atmospheric temperatures, a major factor in the extreme warming observed during the heat dome event. The researchers note that this complex interaction between Earth’s atmosphere and terrestrial landscape reveals a fundamental truth about extreme weather conditions: they do not occur in isolation but are the result of a series of interconnected processes.

Natural processes include atmospheric dynamics such as air pressure and temperature changes, ocean currents, and natural climate cycles, while human-induced climate change involves changes in the Earth’s atmosphere due to greenhouse gas emissions, deforestation, and urbanization. It is the synergy between these natural and human-driven processes that shapes the frequency, intensity and characteristics of these weather phenomena.

The team’s work provides insight into the mechanisms of this heat wave and identifies the important roles of amplified atmospheric circulation patterns and soil moisture, an interaction that created the ideal conditions for heat dome formation.

First author Xiuqi Li, a postdoctoral researcher in Mann’s research group, explains that the phenomenon known as quasi-resonant amplification (QRA) indirectly paved the way for a heat dome, “contributing to soil moisture deficiency, which, in turn, exacerbates global warming in Low atmosphere.

Lee points out that an issue in paleoclimate science has been the ability of models to accurately replicate the intensity and frequency of extreme weather events. This difficulty is largely due to uncertainty about how atmospheric circulation and dynamics will respond to climate change. Their study underscores the need to incorporate planetary wave dynamics into these models by incorporating QRA, which can significantly enhance the prediction accuracy of rare but impactful weather events.

“It is exciting to discover prior feedback mechanisms on how QRA events influence past atmospheric conditions – in this case, through land surface processes,” says Lee. “This provides an additional, albeit indirect, mechanism through which QRA influences extreme heat events.”

This discovery holds promise for predicting extreme “heat dome” events and developing more accurate climate models.

Michael E. Mann is the Presidential Distinguished Professor in the Department of Earth and Environmental Sciences in the College of Arts and Sciences at the University of Pennsylvania and director of the Penn Center for Science, Sustainability, and Media. He received a secondary appointment to the Annenberg School for Communication.

Xiuqi Li is a postdoctoral researcher at the Mann Research Group at Penn.

Other authors are Shannon Christiansen and Judit Cariou of Pennsylvania. Michael F. Wiener of Lawrence Berkeley National Laboratory; and Stefan Rahmstorf and Stefan Petry from the University of Potsdam.

This work was supported by the College of Arts and Sciences at the University of Pennsylvania and the Department of Energy (Contract No. DE340AC02-05CH11231.)

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