In the face of potentially catastrophic effects on global food production, some have proposed drastic solutions to counteract climate change such as reflecting sunlight away from the Earth. A new study from the Carnegie Institution for Science examining the effects of sunshade geoengineering has concluded that such an approach would be more likely to improve food security than threaten it.
Just as large volcanoes cool the planet by ejecting massive amounts of small particles into the stratosphere, one sunshade geoengineering proposal would involve using high-flying airplanes to release small particles in the stratosphere that would scatter sunlight back into space. Just like the volcanic particles, these would fall back to Earth within a year so they would have to be constantly replenished to stop the planet heating back up. The fear is that such an approach could have unintended consequences for the climate, particularly in terms of its effect of precipitation.
While climate change in recent decades has been found to negatively affect crop yields in many regions, a new study led by Carnegie's Julia Pongratz is the first to examine the potential effect of geoengineering on food security. To assess the impact of sunshade geoengineering on crop yields, Pongratz's team, which included Carnegie's Ken Caldeira and Long Cao, as well as Stanford University's David Lobell, used two different climate models.
The team first simulated climates with CO2 levels similar to what exists today. A second set doubled CO2 levels to simulate levels that could be reached in several decades if current trends in fossil-fuel burning continued unabated. A third set doubled the levels of CO2, but with a layer of sulfate aerosols in the stratosphere deflecting about two percent on incoming sunlight away from Earth. The team then applied the simulated changes to crop models that are commonly used to project future yields.
They found that for both current and doubled CO2 levels, sunshade geoengineering would lead to increased crop yields in most regions. This because while such an approach would reduce temperatures by deflecting sunlight back into space, it wouldn't affect the levels of CO2.
"In many regions, future climate change is predicted to put crops under temperature stress, reducing yields. This stress is alleviated by geoengineering," Pongratz said. "At the same time, the beneficial effects that a higher CO2 concentration has on plant productivity remain active."
While the researchers say sunshade geoengineering would improve crop yields overall, the models also predict that some areas would be negatively affected. They also point out that there are other factors to consider, such as the deployment of such a system leading to political or military conflict, and the fact it ignores the acidification of the ocean, which is also caused by CO2 emissions. It would also affect the electricity-generation capabilities of solar power plants.
"The real world is much more complex than our climate models, so it would be premature to act based on model results like ours," Caldeira said. "But desperate people do desperate things. Therefore, it is important to understand the consequences of actions that do not strike us as being particularly good ideas."
"The climate system is not well enough understood to exclude the risks of severe unanticipated climate changes, whether due to our fossil-fuel emissions or due to intentional intervention in the climate system," says Pongratz. "Reducing greenhouse gas emissions is therefore likely a safer option than geoengineering to avert risks to global food security."