Global dimming may mitigate warming, but could hurt crop yields

Author: Carolyn Gramling / Source: Science News

illustration of global dimming — SHADED PLANET Solar geoengineering proposals could combat global warming by injecting reflective particles (blue) into the atmosphere above clouds (grey). By reflecting and scattering light, the particles could cool Earth’s temperature and alter rainfall patterns.
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But that also could reduce the growth of crops (green).

Shading Earth by adding a veil of particles to the upper atmosphere may help to offset global warming — but at a cost.

Crop yields could decline, as they did following two colossal volcanic eruptions that shot sunlight-blocking sulfur particles high above the cloud layer and into the planet’s stratosphere, researchers report online August 8 in Nature. The study is the first to use real-world data to evaluate the potential consequences of such “stratospheric veil” geoengineering.

Adding tiny particles called aerosols to the stratosphere, an approach known as solar radiation management, has been proposed as a way of reducing incoming sunlight to cool the planet and mitigate climate change. Some researchers have suggested that this cooling, as well as the scattering of light by the aerosols, could be beneficial to plants and improve crop yields.

But by looking at harvests of maize, soy, rice and wheat following volcanic eruptions in 1982 and 1991, scientists determined that these sulfates decreased total incoming solar radiation enough to hurt crop yields in the aftermaths of those eruptions.

The team also made projections for how solar radiation management might affect crops in 2050–2069. Those results suggest that any benefits to crops from cooling would be completely offset by decreased food production as a result of reduced sunlight.

Many scientists have been leery of proposed geoengineering schemes to alter incoming sunlight because the potential side effects are largely unknown (SN 3/7/15, p. 14). Stratospheric aerosols reduce how much direct sunlight reaches the surface of Earth, but increase diffuse light reaching the surface. Previous studies have found that the boost in diffuse light may increase plant growth by allowing more light to penetrate tree canopies and reach more leaves. But the potential effect of this dimming on edible yields from crops hadn’t been quantified.