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Potential risk of Stratospheric Aerosol Injection (SAI): agricultural impacts

Summary​

Stratospheric aerosol injection (SAI) could significantly impact global agriculture through altered sunlight availability, weather pattern changes, and ozone layer effects. While aiming to cool Earth by scattering sunlight, SAI might reduce crop yields by limiting photosynthesis as a consequence, yet it also could enhance plant growth through light diffusion reaching other areas of the plant. Regional precipitation changes could disrupt vital agricultural cycles, particularly in monsoon-dependent regions. Ozone depletion risks increasing harmful UV radiation exposure, though reduced tropospheric ozone might benefit crops. Current climate change impacts on agriculture - including heat stress, droughts, and flooding - highlight the complex trade-offs in considering SAI interventions.

Stratospheric aerosol injection (SAI) could impact agricultural systems in a number of ways. The intended goal of an SAI program is the controlled release of aerosols into the stratosphere to scatter incoming sunlight, thereby reducing the amount of light that reaches the Earth's surface, and subsequently, lower global temperatures. As almost all plants are dependent on sunlight for photosynthesis, any change to lighting conditions will have an influence on plant growth. A worldwide geoengineering project like SAI is also expected to cause perturbations in the Earth's delicate climate systems which could influence regional weather and precipitation patterns that play a vital role in regulating agriculture. However, ignoring the enormous benefits that halting climate change will have on global food production, there are also a handful of potential benefits that SAI may have on agricultural systems.

Reduction of sunlight reaching plants​

An intended and vital outcome of SAI is the reduction in sunlight that reaches the Earth's surface via the scattering of incoming light. The required amount of negative radiative forcing (the amount of energy that will be prevented from reaching the Earth's surface by SAI intervention measured in W/m²) varies widely in the research as it depends on estimations of future assumptions of fossil fuel reductions, as well as methods of SAI deployment that are as of yet untested 1 2. Some modeling of the reduction in quality of sunlight following SAI has shown reductions in crop yields for maize, soy, rice, and wheat 3; however, these reductions are roughly equal to the benefits reached by cooling the planet 4. There is a growing body of research that is exploring the potential of SAI to increase light availability to plants, as the multidirectional scattering of sunlight could result in greater levels of photosynthesis on areas of plants that usually do not receive as much sunlight 3 5. It is hypothesized that this phenomenon led to the observable reductions of atmospheric carbon dioxide (CO₂) in the years following the eruption of Mt. Pinatubo in 1991 6.

Weather and precipitation pattern changes​

The Earth's climate is a delicate system of feedback loops that are mostly governed by heat transfer and thermal gradients throughout the Earth's surface and atmosphere. Large perturbations in atmospheric conditions via SAI are expected to alter both local and global weather patterns, mainly through changes to precipitation patterns. Large portions of global food production rely on seasonal precipitation patterns such as the monsoon seasons in Africa and Asia, and the wet season in South America 3. Due to the net reduction in sunlight reaching the Earth's surface as a result of SAI, global precipitation levels are expected to reduce as less water is evaporated from the surface of the Earth 3.

Ozone depletion and UV damage to plants​

Destruction of the Earth's ozone layer and the accompanied increase in UV radiation that would reach the surface is one of the major concerns related to SAI 1. It is well understood that increased levels of UV radiation can directly damage the DNA of living organisms, while also affecting important functions such as growth regulators, pigmentation, and photosynthesis 7. Modeling of SAI has also shown that ozone in the troposphere (the lower atmosphere) would decrease due to global temperature reductions 8. Reduction in tropospheric ozone, which is poisonous to plants, may result in healthier plant growth and increased crop yields 3.

Agriculture is suffering from climate change​

When considering the potential risks of SAI on agriculture and global food systems, it is important to first consider the fact that agriculture is already being impacted by climate change. Estimates vary on how much agriculture will be further affected as the climate crisis worsens, with some studies stating that global grain production could decrease by up to 30% 9. Increased incidence of regional flooding and drought that accompany climate change are already forcing farmers to find new forms of adaptation or change to new crops 3. Global crop yields are also highly susceptible to heat stress caused by rises in global average temperatures, which increases the frequency of heat waves 10.

Sources​

Footnotes​

  1. Crutzen, P. J. (2006). Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma? Climatic Change, 77(3-4), 211-220. https://doi.org/10.1007/s10584-006-9101-y ↩ ↩2

  2. Smith, W., & Wagner, G. (2018). Stratospheric aerosol injection tactics and costs in the first 15 years of deployment. Environmental Research Letters, 13(12), 124001. https://doi.org/10.1088/1748-9326/aae98d ↩

  3. Tracy, S. M., Moch, J. M., Eastham, S. D., & Buonocore, J. J. (2022). Stratospheric aerosol injection may impact global systems and human health outcomes. Elem Sci Anth, 10(1), 00047. https://doi.org/10.1525/elementa.2022.00047 ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  4. Proctor, J., Hsiang, S., Burney, J., Burke, M., Schlenker, W., & Miguel, E. (2018). Estimating global agricultural effects of geoengineering using volcanic eruptions. Nature, 560(7719), 480-483. https://doi.org/10.1038/s41586-018-0417-3 ↩

  5. Cohan, D. S., Xu, J., Greenwald, R., Bergin, M. H., & Chameides, W. L. (2002). Impact of atmospheric aerosol light scattering and absorption on terrestrial net primary productivity. Global Biogeochemical Cycles, 16(4), 1090. https://doi.org/10.1029/2001GB001441 ↩

  6. Gu, L., Baldocchi, D., Wofsy, S. C., Munger, J. W., Michalsky, J. J., Urbanski, S. P., & Boden, T. A. (2003). Response of a deciduous forest to the Mount Pinatubo eruption: Enhanced photosynthesis. Science, 299(5615), 2035-2038. https://doi.org/10.1126/science.1078366 ↩

  7. Hollósy, F. (2002). Effects of ultraviolet radiation on plant cells. Micron, 33(2), 179-197. https://doi.org/10.1016/S0968-4328(01)00011-7 ↩

  8. Eastham, S. D., Weisenstein, D. K., Keith, D. W., & Barrett, S. R. H. (2018). Quantifying the impact of sulfate geoengineering on mortality from air quality and UV-B exposure. Atmospheric Environment, 187, 424-434. https://doi.org/10.1016/j.atmosenv.2018.05.047 ↩

  9. Gupta, G. P. (2020). Role of global climate change in crop yield reductions. In P. Saxena & A. Srivastava (Eds.), Air pollution and environmental health (pp. 95-110). Springer. https://doi.org/10.1007/978-981-15-3481-2_5 ↩

  10. Teixeira, E. I., Fischer, G., van Velthuizen, H., Walter, C., & Ewert, F. (2013). Global hot-spots of heat stress on agricultural crops due to climate change. Agricultural and Forest Meteorology, 170, 206-215. https://doi.org/10.1016/j.agrformet.2011.09.002 ↩