Reach for the Sky! Or, Maybe Not.
What Geoengineering With Aerosols Could Mean for Climate Change
What would you do to end the warming effects of climate change in your lifetime? Would you attend a climate rally? Go vegan? Realistically, you’d need to do a lot more than that to make a noticeable difference. Now, what if you didn’t need to do anything at all? This is the thought process of many individuals promoting the theoretical geoengineering technique of using aerosols to reduce the amount of solar radiation reaching Earth’s surface.
More specifically, Stratospheric Aerosol Injection (SAI), as its name would suggest, is a proposed method of solar modification that involves injecting aerosols into the stratosphere. Aerosols are minute particles of sulfuric acid that combine with water droplets and, when suspended in the stratosphere, scatter, absorb, and ultimately reflect 1% of incoming sunlight back into space. The cooling effects are shockingly immediate and effective, with some models predicting noticeable global cooling for one to two years after injection. Longer-term effects will need longer-term injections–and less sulfuric acid than you might think. According to research by David Keith, a leading advocate for solar geoengineering and professor of applied physics at Harvard University, if operations were to begin right away, it would take 25,000 metric tons of sulfuric acid to cut global warming in half within a year. Then by 2040, 250,000 metric tons would be injected at an annual cost of $700 million to compensate for increasing carbon dioxide levels. Compared to the estimated 145 billion dollars in damages due to climate-related disasters in 2021 in the US alone, aerosols are extremely cost-effective to implement. Keith’s estimates also give an idea of how aerosols directly offset greenhouse gas emissions, with a few grams suspended in the stratosphere offsetting the warming caused by one ton of CO2.
How do we know this would (probably) work? Solar modification is relatively untested—by humans. Volcanoes naturally modify incoming solar radiation when they erupt. Eruptions propel large amounts of sulfur dioxide that turns into aerosols in the stratosphere. When Mt. Pinatubo in the Philippines erupted on June 15, 1991, it cooled the globe by 1°C in the months that followed. Researchers like Keith are confident that human-made aerosols would have a similar effect with appropriate implementation. Unintentional implementation, like the 50 million metric tons of sulfur emitted by the burning of fossil fuels every year, is not as effective. Most of those pollutants are left in the lower atmosphere, where they get dispersed in a few days, while a smaller percentage enters the stratosphere and has a cooling effect. Technology that could inject aerosols into the stratosphere already exists and would theoretically be in the form of balloons, towers, and fleets of aircrafts.
Most people are taught early on that when something sounds too good to be true, it usually is–and solutions to the climate crisis are no different. There are severe unintended consequences that are predicted to arise if this theoretical technique is implemented.
One study focused on the scenario of only one country, region, or hemisphere pursuing implementation. Based on their estimates, if only one hemisphere released aerosols regularly, then other regions would experience higher frequencies of droughts and cyclones. If the U.S. and Northern Europe released them regularly, for example, then parts of India and Africa would experience adverse effects. Another study focused on the impacts on the spread of infectious diseases such as malaria in futures modeled with and without solar geoengineering. The results indicated that although aerosols would cool the tropics and reduce transmission, they would simultaneously increase transmissions in Sub-Saharan Africa and Southern Asia. Malaria spreading mosquitoes thrive in environments between 25 to 34°C and, although some places projected to be have increased rates of transmission would now be too cold, many other places projected to be too hot will now be within range. Compared to extreme weather and warming, the models estimated that this geoengineering technique would nullify a reduction of 1 billion people in the Southern Hemisphere to be at risk of malaria. Environmental inequality is not a new or future issue; consequences of global warming have never been equally distributed across nations. The global south, which contributes the least to climate change, often experiences the harshest effects such as heatwaves, droughts, flooding, and agricultural loss. These regions that are most at risk from solar geoengineering are often least included in discussions.
Weaponizing environmental modification technologies is not a new phenomenon. The U.S use of cloud-seeding during the Vietnam War was one instance where the weather was modified to influence warfare. Although aerosol injection is not as precise as cloud seeding, as it cannot be targeted at one region alone, it would have a significant destabilizing effect. Because of its extreme and unpredictable effects, it would not be wise to disregard the potential of SAI’s further development for weaponized use.
Despite the severe effects that could arise while aerosol injection is in use, the most concerning and debated consequence surround what would happen if we suddenly stopped– which would result in a phenomenon known as termination shock. Since solar geoengineering would be masking the effects of global warming by cooling the planet despite rising greenhouse gas emissions, then suddenly stopping would lead to a rapid increase in temperatures. Aerosol implementation could be stopped because of a change in policy, conflict, or a natural disaster—and the results could be devastating. Concentrations of greenhouse gasses would continue to rise during geoengineering, and the temperature would accelerate towards what it would have been without the aerosols once the implementation ceases. This means that temperature changes we expect to see over the next century could occur in a couple decades, giving humans and ecosystems even less time to adapt to extreme weather conditions due to climate change.
Regardless of whether solar geoengineering through the use of aerosols does more harm than good—researching it is important while simultaneously acknowledging the need to decarbonize. Global warming is happening right now, and countless consequences not addressed by solar modification are increasingly evident and irreversible. Ocean acidification, biodiversity loss, and drought, to name a few, will continue if warming ceases but emissions continue. However, looking into and developing techniques that can help mitigate warming while global industries and corporations attempt to transition off of fossil fuels is vital to maintaining a livable planet. If we don’t transition in time, future generations will need to make a choice—and to help them become more knowledgeable, we need to explore all our options.