Research from the Harvard John A Paulson School of Engineering and Applied Sciences (SEAS) has found that solar geoengineering may be effective in alleviating some of the worst impacts of global warming on crops.
The research looked at three types of solar geoengineering – stratospheric aerosol injection, marine sky brightening, and cirrus cloud thinning – and their impact on the global yield of maize, sugarcane, wheat, rice, soy and cotton in a business-as-usual future where emissions continue at their current levels.
In such a future, the most effective way to protect crops against the worst effects of global climate change is to reduce the surface temperature. The researchers found that all three potential solar geoengineering methods have a strong cooling effect that would benefit crop yields.
“Research on solar geoengineering must address whether or not it is effective at reducing human impacts of climate change,” said David Keith, professor of applied physics at SEAS and professor of public policy at the Harvard Kennedy School. “Our paper helps fill that gap by using the best crop model yet embedded in a climate model to examine the potential impact of solar geoengineering on agricultural yields.”
Previous research suggested that cooling temperatures brought on by stratospheric aerosol injection may also lead to less rainfall, which could result in yield loss for rainfed crops. But, according to SEAS, these studies didn’t look at one of the most important ecological factors in crop transpiration and productivity – humidity.
“Relative humidity or vapor pressure deficit has stronger control on plant water use and crop productivity than precipitation,” said Yuanchao Fan, a Fellow in the Harvard Solar Geoengineering Research Program and first author of the paper. “We found that in a cooler world under multiple scenarios, except cirrus cloud thinning, there will be higher relative humidity, which will alleviate water stress for rainfed crops. Our model shows that the change in precipitation resulting from all three solar geoengineering methods would, in fact, have very little effect on crops.”
The researchers compared how agricultural productivity is affected by solar geoengineering and emissions reductions. The researchers found that while emissions reductions have strong cooling and humidity benefits, they may have a smaller benefit for crop yields than solar geoengineering because the reduction of CO2 fertilization reduces the productivity of most crops compared with solar geoengineering that achieves the same temperature reduction.
The findings highlight the need to combine emissions reductions with other tools, including increasing the use of nitrogen fertilization and changes to land use.
The research was a collaboration between SEAS and the Norwegian Research Centre and the Bjerknes Centre for Climate Research, the Norwegian University of Science and Technology, the National Center for Atmospheric Research, Seoul National University and the Chinese Academy of Sciences. Read the full paper here: Nature Food.
