The Effects of Solar Radiation Management Geoengineering on Global Crop Yields

Climate change studies have demonstrated an increase in global mean temperature. This increase in temperature has detrimental affects for both the environment and human health. It has also been predicted that climate change may have adverse effects on crop yields. For this reason, solar radiation management (SRM) has been discussed as a method to mitigate climate change and global warming. While the effects of SRM could combat climate change, it could also threaten food and water supply for billions of people. Pongratz et al. (2012) use climate models to simulate the effects of a geoengineered climate on global crop yields. The authors found that crop yields increase in the model with SRM in a high-CO2 climate. They reason that the reduction of temperature stresses while maintaining the benefits of CO2 fertilization account for this result. However, they conclude that even so, with the many potential adverse consequences of geoengineering, the best way to protect crop yields is to reduce greenhouse gas emission. —Michela Isono
Pongratz, J., Lobell, D., Cao, L., Caldeira, K., 2012. Crop Yields in a Geoengineered Climate. Natural Climate Change, 10.1038.

            Global warming has become a main topic of focus within the scientific community. To counteract this effect, geoengineering techniques have been discussed as a mitigation method. Specifically, SRM has been proposed because of its ability to deflect sunlight away from the planet and reduce the amount of solar insolation absorbed. However, SRM also affects precipitation rates. For this reason, crop yields could be adversely affected. Pongratz et al. studied the impacts of changes in temperature, precipitation and the atmospheric CO2 concentration on crop yields.
            Methods: Pongratz et al. combined climate-model simulations with models of crop-yield responses to climate changes. Three global climate simulations were used: a climate to represent today’s environment with an atmospheric concentration of CO2 of ~400ppm (control); a climate with twice the amount of CO2 (2 x CO2); and a climate with twice the amount of CO2 and sulphate aerosols to stabilize global mean temperatures at control levels (SRM). The models are used to isolate the effects of a high-CO2 environment with and without SRM compared with the present-day climate. The crops used are: wheat, maize, and rice. These crops were chosen because they provide about half of the calories consumed by humans and a large fraction of calories consumed by livestock.
            Results and Discussion: When comparing results from 2 x CO2 and SRM with control for all three crops, 2 x CO2 showed much lower percent yield and production than SRM, where 2 x CO2 also showed a negative percentage yield and production for maize when compared to control (meaning the control model produced more yield and had a greater production). This result was due to the detrimental influences of climate change and the beneficial influences of CO2 fertilization. Warming climate changes at most latitudes have negatively effect maize and wheat yields. In contrast, the increased temperatures may benefit rice at high latitudes by enabling a longer growing season. The yield decreases at low latitudes are a result of heat and drought. CO2 fertilization also greatly compensated for yield losses of maize, and yield increases of wheat and rice.
            In the SRM compared to the control, the yields and production increased for all three crops across all latitudes. This is due to the effects of CO2 fertilization. However, there were few small negative impacts on yields across some latitudes in the SRM, but these impacts were smaller than in the 2 x CO2 case.
In the SRM compared to 2 x CO2 case, a significant loss in yield was only shown for rice growing at high altitudes. The production of maize, wheat and rice was higher under SRM than 2 x CO2overall. Therefore, the simulations demonstrated that SRM would create an increase in global yields compared to the global yields in a 2 x CO2climate.
Even with a stabilized temperature, specific regions may experience different changes in their yield and crop productivity due to climate changes. The authors concluded that their simulations counter concerns about SRM threatening food security in large regions, but small regions may also experience greater changes in yields. This may endanger local food security and shift market shares and producer ranking.
In conclusion, the authors did not final substantial reductions in yields by SRM compared to the control. Warming, rather than precipitation change, caused most of the climate-induced yield reductions. When SRM was applied in the high-CO2 climate, the yields and production of maize, wheat and rice increased at the global mean temperature and across most latitudes. This phenomenon represents stabilization in temperature, reduced CO2 levels, and beneficial effects of CO2 fertilization on plant productivity.
Recommendations: Because the effects of climate change on a global scale is better understood than on a regional scale, the authors stated that more research is needed to better understand the effect of SRM on a smaller geographical scale. The authors do not believe that SRM can maintain the economic status quo because market shares of agricultural output will change with climate changes. Therefore,an analysis of the environmental and socioeconomic consequences of SRM is needed as well. Lastly, the authors stated that further research is needed to understand the anticipated and unanticipated effects of SRM. 

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