Scientists know that aerosol particles can temporarily cool the earth’s surface. Fine ash from the 1991 eruption of Mount Pinatubo — the largest volcanic eruption in the last 100 years — lowered global temperatures by 0.5 degrees Celsius (0.9°F) for almost two years. They know therefore, that blocking the sun’s rays with an artificial particle shield launched high into Earth’s atmosphere to curb global temperatures is a technological fix. As the effects of climate warming become ever more serious, this possibility is gaining traction as a last resort for containing the climate crisis.
Large-scale geoengineering proposals have bordered on science fiction for decades. But in recent years, these technologies have seeped into mainstream climate discussions as a last-ditch policy option, garnering attention and millions in funding.
In 2019, the United States Congress granted the National Oceanic and Atmospheric Administration (NOAA) $4 million for solar geoengineering research. In March 2021, the U.S. National Academies of Sciences, Engineering, and Medicine, called for the country to spend an additional $100 to $200 million. Billionaire Bill Gates has made personal donations to the world’s leading solar geoengineering research unit at Harvard University.
But to offset global warming caused by carbon emissions, an artificial aerosol particle shield would need to be continuously replenished over several decades, running contrary to a goal of the United Nations Framework Convention on Climate Change to prevent “dangerous human interference with the climate system.”
If stopped abruptly, the protective aerosol cloud’s masking cooling effect would quickly abate allowing all the accumulated greenhouse gases in the atmosphere to hit the planet in one rush. Global temperatures could suddenly skyrocket four to six times faster than recent climate change, according to a 2018 Yale study published in Nature Ecology & Evolution.
The color of the sky could change. The chemical composition of the ozone layer and oceans may be permanently altered. Photosynthesis, which depends on sunlight, may slow down, possibly harming biodiversity and agriculture. And global weather patterns could change unpredictably. “How can we give a guarantee to future generations that our governance systems are so robust that there would be no termination shock?” questioned Aarti Gupta, a professor of Global Environmental Governance at Wageningen University. The list of unknowns is long and worrisome.
More than 60 academics signed an open letter, including Dirk Messner, the president of the German Environment Agency; Cambridge University climatologist Mike Hulme; Åsa Persson, the Stockholm Environment Institute’s research director; and award-winning author Amitav Ghosh. They’re calling on political institutions to place limits on solar geoengineering research so that it cannot be deployed unilaterally by countries, companies or individuals.
“Some things we should just restrict at the outset,” said Gupta, one of the open letter’s lead authors. Gupta placed solar geoengineering in the category of high-risk technologies, like human cloning and chemical weapons, that need to be off-limits. “It might be possible to do, but it’s too risky,” she told Mongabay in an interview.
Despite the potential dangers, no mechanism exists today to stop an individual, company or country from launching a solo mission, said Gupta. To prevent this, the open letter suggests five urgent protective measures: no outdoor experiments, no implementation, no patents, no public funding, and no support from international institutions such as the United Nations.
Last year, the Harvard team was forced to cancel their first outdoor geoengineering test, to be done in partnership with Sweden’s Space Corporation, following a Swedish public protest led by the Indigenous Sami people.
“You can model it and conduct experiments, but we can only know the final effects of planetary-scale solar geoengineering after its deployment,” warned Frank Biermann, professor of global sustainability governance at Utrecht University and one of the letter’s initiators, in a telephone interview; he supported the Sami-led opposition against Harvard’s high-altitude test flight. “It is an extremely risky proposition,” he concluded.
“The best option is to keep the genie in the bottle and not start with these very dangerous technologies,” said Biermann. “We need to focus not on these fantasies of nonexistent technologies, but on the real problem at hand, which is decarbonization.”
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