MIT NEWS OFFICE Study: Reflecting sunlight to cool the planet will cause other global changes Jennifer Chu Tuesday, June 2, 2020

How can the world combat the continued rise in global temperatures? How about shading the Earth from a portion of the sun’s heat by injecting the stratosphere with reflective aerosols? After all, volcanoes do essentially the same thing, albeit in short, dramatic bursts: When a Vesuvius erupts, it blasts fine ash into the atmosphere, where the particles can linger as a kind of cloud cover, reflecting solar radiation back into space and temporarily cooling the planet.

Some researchers are exploring proposals to engineer similar effects, for example by launching reflective aerosols into the stratosphere — via planes, balloons, and even blimps — in order to block the sun’s heat and counteract global warming. But such solar geoengineering schemes, as they are known, could have other long-lasting effects on the climate.

Now scientists at MIT have found that solar geoengineering would significantly change extratropical storm tracks — the zones in the middle and high latitudes where storms form year-round and are steered by the jet stream across the oceans and land. Extratropical storm tracks give rise to extratropical cyclones, and not their tropical cousins, hurricanes. The strength of extratropical storm tracks determines the severity and frequency of storms such as nor’easters in the United States.

The team considered an idealized scenario in which solar radiation was reflected enough to offset the warming that would occur if carbon dioxide were to quadruple in concentration. In a number of global climate models under this scenario, the strength of storm tracks in both the northern and southern hemispheres weakened significantly in response.

Weakened storm tracks would mean less powerful winter storms, but the team cautions that weaker storm tracks also lead to stagnant conditions, particularly in summer, and less wind to clear away air pollution. Changes in winds could also affect the circulation of ocean waters and, in turn, the stability of ice sheets.

“About half the world’s population lives in the extratropical regions where storm tracks dominate weather,” says Charles Gertler, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “Our results show that solar geoengineering will not simply reverse climate change. Instead, it has the potential itself to induce novel changes in climate.”

Gertler and his colleagues have published their results this week in the journal Geophysical Research Letters. Co-authors include EAPS Professor Paul O’Gorman, along with Ben Kravitz of Indiana University, John Moore of Beijing Normal University, Steven Phipps of the University of Tasmania, and Shingo Watanabe of the Japan Agency for Marine-Earth Science and Technology

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