Atmospheric Aerosols Have Stronger Impact on Extreme Weather Events

According to researchers at the Jet Propulsion Laboratory (JPL) and California Institute of Technology (Caltech), the change in winter weather patterns in northern Eurasia and Europe is linked to reduced air pollution.

A reduction in aerosol production in Europe has led to fewer extremely cold days
A reduction in aerosol production in Europe has led to fewer extremely cold days. Image Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio.

In the last five decades, the occurrence of very cold days has reduced across northern Eurasia, which also includes Russia, and Europe. The integration of an advanced climate model with long-term observations demonstrated what scientists term an “unambiguous signature” of the reduction of man-made aerosols discharged over that time.

This phenomenon has led to changes in surface-temperature variability and the wintertime Northern Hemisphere polar jet stream (a rapidly moving channel of air that flows from west to east) during that period.

The study indicates that aerosols can have a major effect on extreme winter weather when compared to regional-scale greenhouse gases, even though it is difficult to decode the association between extreme weather events and aerosols. Aerosols are solid particles that pollute the air from various activities such as burning coal.

This discovery underscores the importance of understanding the effects of anthropogenic aerosols for accurate climate projection of extreme weather events, which is crucial to formulating climate mitigation and adaption strategies.

Yuan Wang, Study Lead Author and Staff Scientist, Caltech and JPL

Caltech manages JPL for NASA. Wang’s study relating to this research was published in the Nature Climate Change journal on February 3rd, 2020.

Along with his collaborators, Wang observed that more rigorous air pollution regulations caused a decline in atmospheric aerosols. Because fewer particles were present in the air to reflect sunlight, this led to a local warming effect.

In Europe, warmer temperatures caused a more pronounced temperature gradient between the North Pole and Europe, which consequently made it possible to lock the jet stream into a steady and comparatively straight position.

As the jet stream twists or bends, dipping south, it can transport cold arctic air to more southern latitudes. It has been predicted by certain climate models that the steady rise of the arctic temperature, induced by greenhouse gas-driven global warming, can potentially weaken the jet stream and cause it to twist or bend. However, Wang’s research team has identified an underlying mechanism that is more complicated.

This tells us that for winter extremes, aerosols have a greater impact than greenhouse gases.

Jonathan Jiang, Study Co-Corresponding Author, JPL, NASA

Jiang handled the research and is the co-corresponding author of the Nature Climate Change study.

Because it is anticipated that China will implement air pollution regulations that will result in reduced atmospheric aerosols over the next 20 to 30 years, the climate model estimates that an analogous effect could also be observed over eastern Asia.

The title of the study is “Reduced European aerosol emissions suppress winter extremes over northern Eurasia.” Co-authors of the study are Yuk Yung, professor of planetary science and JPL senior research scientist; John Seinfeld, the Louis E. Nohl Professor of Chemical Engineering; Caltech graduate student Tianhao Le; Gang Chen of UCLA; and Hui Su of JPL.

The study was financially supported by the National Science Foundation and NASA.

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