Carbon dioxide emissions from the burning of coal, oil, and gas have been increasing over the past decades, causing the Earth to get hotter and hotter. There are concerns that a continuation of these trends could have catastrophic effects, including crop failures in the heat-stressed tropics. This has led some to explore drastic ideas for combating global warming, including the idea of trying to counteract it by reflecting sunlight away from the Earth. However, it has been suggested that reflecting sunlight away from the Earth might itself threaten the food supply of billions of people. New research led by Carnegie’s Julia Pongratz examines the potential effects that geoengineering the climate could have on global food production and concludes that sunshade geoengineering would be more likely to improve rather than threaten food security. Their work was published online by Nature Climate Change Jan. 22.

Big volcanoes cool the planet by placing lots of small particles in the stratosphere, but the particles fall out within a year and the planet heats back up. One proposal for cooling the planet is to use high-flying airplanes to constantly replenish a layer of small particles in the stratosphere that would scatter sunlight back to space. But such so-called sunshade geoengineering could have unintended consequences for climate, and especially for precipitation.

Although scientists know that climate change in recent decades has negatively impacted crop yields in many regions, the study by Pongratz and colleagues is the first to examine the potential effect of geoengineering on food security. Pongratz’s team, which included Carnegie’s Ken Caldeira and Long Cao, as well as Stanford University’s David Lobell, used models to assess the impact of sunshade geoengineering on crop yields.

Using two different climate models, they simulated climates with carbon dioxide levels similar to what exists today. A second set of simulations doubled carbon-dioxide levels – levels that could be reached in several decades if current trends in fossil-fuel burning continue unabated. A third set of simulations posited doubled carbon dioxide, but with a layer of sulfate aerosols in the stratosphere deflecting about 2% of incoming sunlight away from the Earth. The simulated climate changes were then applied to crop models that are commonly used to project future yields.