In 1991, Mount Pinatubo in the Philippines erupted, becoming the second largest volcanic eruption of the 20th century. Its ash plume shot up past the atmosphere and into the stratosphere, dispersing a layer of aerosol particles around the world. These particles formed a sort of solar umbrella that reflected sunlight away from the Earth, causing global temperatures to drop by about half a degree Celsius for almost two years. This is not the first massive volcanic eruption to cool global temperatures; El Chichón volcano lowered temperatures by a similar amount in 1982, as did other major eruptions over the past century.
Today, scientists have been exploring whether we could replicate this phenomenon to fight global warming using a technology called solar geoengineering. Supporters say it’s a tool we need to seriously explore as climate change worsens, understanding more about these things that could potentially reduce suffering. Critics, however, believe the technology’s risks outweigh its rewards and shouldn’t be a response to fighting global warming.
To understand the benefits and risks of solar geoengineering, I spoke to several scientists, lawyers, and indigenous leaders with strong opinions on both sides. With stakes as high as the survival of the human race on Earth, should we be exploring solar geoengineering?
There’s one thing scientists all agree on: solar geoengineering could cool down the planet by reflecting sunlight away from the Earth, stopping heat from getting trapped in our atmosphere. We could do that by injecting aerosols into the stratosphere, like volcanoes can do. Some scientists are also looking into brightening marine clouds so they’re better at reflecting the sun, and other potential methods include reflective shields in outer space.
These initiatives are still in different stages of the research phase, but in order for us to deploy these technologies and get large scale cooling effects, we’d need to interfere with our complex climate on a massive scale. One of the main reasons some scientists support solar geoengineering is that we’re currently on a pretty dire path. Our emissions, mainly carbon dioxide, keep rising, and there’s really no question we must cut emissions in the long run.
But even if we cut emissions to zero tomorrow, that does not eliminate climate risk; it just means we stop the climate risk getting worse because the climate risk comes from accumulated emissions. That’s University of Chicago professor David Keith. He explained to me that unless we think beyond emission reduction, the climate change impacts we’re already experiencing will continue to worsen.
Adding new elements into our atmosphere or stratosphere will change precipitation patterns across the world, potentially worsening the extreme weather we’re already experiencing due to climate change. Nearly everyone agrees on these risks. You can’t actually answer the most significant questions about the climate system response short of a full scale deployment. A full-scale deployment of solar geoengineering would require unprecedented global cooperation not only in terms of scale, but also in terms of time. The carbon dioxide we have emitted since the industrial revolution and continue to emit today will have a warming effect on climate for thousands of years, even if we stop emitting. In contrast, solar geoengineering techniques proposed have a very short lifetime in the atmosphere. To create a continued cooling effect, we would need to deploy them constantly for centuries, requiring institutions and treaties to be adhered to for thousands of years. This is a burden that critics think is ungovernable and unsustainable. In 2021, Sweden rejected a pioneering project to test solar geoengineering technology due to the potential for drastic and unpredictable changes on climate, weather and biodiversity, as well as the geopolitical tensions it might awaken.
Most solar geoengineering research is taking place in labs with models and simulations, which has led to a debate about how far we should take the research. In January of 2022, 400 scientists issued a letter calling for a non-use agreement on solar geoengineering, with five core commitments, among them no outdoor experiments, no public funding and no support from international institutions. Critics of solar geoengineering worry that the more modeling we do, the closer we’ll get to full-scale deployment. However, they acknowledge that some simulations are useful and are a key part of the overall science.
In February of 2023, 110 scientists, including Keith, issued a letter in support of more research into solar geoengineering. They want a robust, international scientific assessment that includes experiments that could potentially advance the technology, but stated that “while we fully support the research, this does not mean we support the use of solar geoengineering tech”. Ultimately, if we make a collective decision now not to do serious research, this does not prevent people from employing the technology in the future. It just means they will deploy it with less knowledge. Doing research on solar geoengineering right now is very important in order to make equitable decisions in the future. People are aware that these options exist, and some believe we should be doing them now. This could lead to people in the future using it as an excuse to keep selling fossil fuels, which would counteract decarbonization efforts. Mexico has banned solar geoengineering experiments, while the US is developing a research plan and world organizations are making assessments and recommendations. Although the path forward is not clear, everyone involved in the issue is passionate about finding a solution to the current climate crisis. This tension between the two sides may be a good thing, as it could lead to more thoughtful and rigorous approaches to the problem.