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Climate Change

Solar geoengineering could depress crop yields, study finds

Researchers draw conclusions from stratospheric aerosols spewed by volcanoes

by Cheryl Hogue
August 16, 2018 | A version of this story appeared in Volume 96, Issue 33


Photo shows a giant ash cloud rising into the sky from the 1991 eruption of Mount Pinatubo in the Philippines.
Credit: USGS archives
In addition to spewing this giant ash cloud, the 1991 eruption of Mount Pinatubo also blew sulfur dioxide into the stratosphere.

As Earth warms because of climate change, society might turn to geoengineering to deflect some of the sun’s radiation and attenuate average global temperature rise. But if humans inject aerosols into the stratosphere to curb the amount of sunlight reaching Earth’s surface, they also might lower yields of crops that feed billions of people, a study finds (Nature 2018, DOI: 10.1038/s41586-018-0417-3)

A team of researchers, led by University of California, Berkeley, economics graduate student Jonathan Proctor, examined the aftermath of two major volcanic eruptions to reach this conclusion—1991’s Mount Pinatubo in the Philippines and 1982’s El Chichón in Mexico. Both explosions shot millions of metric tons of sulfur dioxide into the stratosphere, where it oxidized to form sulfate aerosols. Those tiny particles increased the opacity of the stratosphere and reduced sunlight reaching the surface for years after the eruptions. The researchers studied levels of stratospheric aerosols, solar radiation, and crop production recorded after the eruptions. They found that the presence of the particles depressed yields of key crops, including rice, soy, wheat, and corn. “Shading the planet keeps things cooler, which helps crops grow better,” Proctor says. “But plants also need sunlight to grow, so blocking sunlight can affect growth.” The finding means that intentionally injecting aerosols into the stratosphere to cool the planet “may not be able to substantially lessen the risks that climate change poses to global agricultural yields and food security,” the authors conclude.


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