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Potential risk of Stratospheric Aerosol Injection (SAI): effects on existing climate systems

Summary​

Stratospheric Aerosol Injection (SAI) poses significant risks to Earth's complex climate systems through impacts on precipitation patterns, ocean circulation, and temperature regulation. While intended to mitigate global warming, SAI could reduce global precipitation, alter monsoon patterns, and affect critical systems like the Atlantic Meridional Overturning Circulation. The technology might help slow ice melt and sea level rise but carries risks of abrupt temperature increases if discontinued (termination shock). The interconnected nature of climate systems means even targeted interventions could have unforeseen consequences, emphasizing the need for further research to fully understand potential impacts.

Changes to the Earth's climate and weather patterns pose the greatest risk and uncertainty regarding SAI. The Earth's climate is a delicate system of interconnected feedback loops that can be susceptible to even small perturbations. SAI has the potential to change precipitation patterns, ocean circulation, and temperature patterns, all of which can lead to unexpected and dangerous consequences for life on Earth. While it is important to account for the fact that many of the risks of SAI are similar to the impending risks of unmitigated climate change, the risks that SAI poses for the existing climate system should not be underestimated.

Changes to precipitation patterns​

SAI will result in changes to precipitation patterns on global and regional scales. Globally, average levels of precipitation are expected to reduce as a consequence of the sun-dimming effect of SAI, which results in less evaporation 1. This has been confirmed via analysis of land-based precipitation and river-to-ocean discharge after large volcanic events, which are an analogue to SAI 2. On regional scales, SAI is expected to impact extreme seasonal weather events such as the Asian and African Monsoon seasons. The degree of these changes has a strong dependence on the location and scale of aerosol injection. Nonetheless, modeling has shown that in most cases, SAI will result in lower intensity monsoon and tropical storm seasons through changes in the location of the Intertropical Convergence Zone (ITCZ) 1.

Changes to ocean circulation​

Oceans dictate the Earth's climate and serve as a vital temperature regulator for the planet. These functions are coupled with how much heat the ocean absorbs, so perturbations through SAI are expected to impact this system. Modeling has shown that SAI will alter the distribution of heat and salinity throughout the Earth's oceans 3. Climate simulations have also shown that SAI may lead to a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) by stabilizing ocean air temperature differences and reducing the amount of freshwater inflow into the ocean from melting sea ice 3 4. The AMOC, which is currently slowing down and is at risk of "shutdown" due to climate change, runs throughout the Atlantic Ocean and greatly influences climate patterns in South America, West Africa, and Europe 5.

Changes to temperature​

The largest change to the Earth's climate system as a consequence of SAI is also its main intended outcome: reducing global temperatures. The magnitude of the temperature change is dependent on what is deemed necessary to counteract the effects of climate change, with a higher intensity of aerosol injection resulting in a greater cooling effect. An example of the expected cooling effect on global temperatures can be seen in the eruption of Mount Pinatubo in 1991, which resulted in a global average temperature decrease of around 0.9°F. It is hypothesized that SAI will dampen some of the effects of global warming such as extreme precipitation events and heat waves 4. Simulations have also shown that SAI will significantly reduce the melting of ice caps and slow sea level rise 4. SAI also poses the risk of 'termination shock' when the injection of aerosols is abruptly halted, leading to global temperature rises that are potentially greater than current predictions of unabated climate change depending on the intensity of the injection 6.

General Uncertainty​

It is important to note that the effects of SAI on the climate system are still not well understood, and there is a large degree of uncertainty regarding the potential positive and negative impacts. Climate systems are complex and interconnected. Any rapid perturbation to the system, such as through SAI, can lead to unexpected consequences. It is for that reason that more research in this area is urgently needed to fully understand the potential impacts of SAI.

Sources​

Footnotes​

  1. Huynh, K. A., & McNeill, V. F. (2024). The potential environmental and climate impacts of stratospheric aerosol injection: A review. Environmental Science: Atmospheres, 4(1), 114-143. https://doi.org/10.1039/D3EA00134B ↩ ↩2

  2. Trenberth, K. E., & Dai, A. (2007). Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering. Geophysical Research Letters, 34(L15702). https://doi.org/10.1029/2007GL030524 ↩

  3. Cao, L., Duan, L., Bala, G., & Caldeira, K. (2016). Simulated long-term climate response to idealized solar geoengineering: Effect of long-term solar geoengineering. Geophysical Research Letters, 43(5), 2209–2217. https://doi.org/10.1002/2016GL068079. ↩ ↩2

  4. Tracy, S. M., Moch, J. M., Eastham, S. D., & Buonocore, J. J. (2022, January 4). Stratospheric aerosol injection may impact global systems and human health outcomes. Elementa: Science of the Anthropocene, 10(1), Article 00047. https://doi.org/10.1525/elementa.2022.00047 ↩ ↩2 ↩3

  5. Jackson, L. C., Kahana, R., Graham, T., et al. (2015). Global and European climate impacts of a slowdown of the AMOC in a high resolution GCM. Climate Dynamics, 45, 3299–3316. https://doi.org/10.1007/s00382-015-2540-2 ↩

  6. Tang, A., & Kemp, L. (2021). A fate worse than warming? Stratospheric aerosol injection and global catastrophic risk. Frontiers in Climate, 3. https://doi.org/10.3389/fclim.2021.720312 ↩