Stop Efforts to Darken the Sun and Cool the Earth, Scientists Say

  • Scientists are calling on political institutions to place limits on solar geoengineering research so that it cannot be deployed unilaterally by countries, companies or individuals.
  • Long-term, planetary-level geoengineering interventions of this kind are unprecedented and extremely dangerous, say the academics behind the letter, and should therefore not be experimented with outside, receive patents, public funds or a international support.
  • Solar geoengineering’s leading proposition of injecting billions of aerosol particles into Earth’s stratosphere could have serious, unintended and unforeseen consequences.

There is a last-resort technological solution gaining traction to reduce global temperatures – blocking the sun’s rays with a shield of man-made particles launched high into the Earth’s atmosphere. But a coalition of more than 60 academics wrote in a open letter that this must be stopped.

The academics who signed the open letter and article published in the WIREs (Wiley Interdisciplinary Reviews) online publication on climate change on January 17 features award-winning author Amitav Ghosh; Dirk Messner, President of the German Environment Agency; Mike Hulme, climatologist at the University of Cambridge; and Åsa Persson, research director of the Stockholm Environment Institute.

“Some things we should just restrict initially,” said one of the lead authors of the open letter, Aarti Gupta, professor of global environmental governance at Wageningen University. Gupta placed solar geoengineering in the category of high-risk technologies, such as human cloning and chemical weapons, which must be banned. “It may be possible, but it’s too risky,” she told Mongabay in an interview.

The color of the sky could cash. The chemical composition of the ozone layer and oceans can be permanently changed. Photosynthesis, which depends on sunlight, can slow down, maybe harm biodiversity and agriculture. And global weather patterns could change unpredictably.

Despite the potential dangers, no mechanism exists today to prevent an individual, company or country from launching a solo mission, Gupta said. To avoid this, the open letter suggests five urgent protective measures: no outdoor experiments, no enforcement, no patents, no public funding and no support from international institutions such as the United Nations.

The 1991 volcanic eruption of Mount Pinatubo in the Philippines threw enough sulfate and other aerosol particles into the stratosphere to cool the Earth. Photo taken by Sgt. Val Gempis.

Solar geoengineering: Too many risks

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 100 years – lowered global temperatures by 0.5 degrees Celsius (0.9°F) for nearly two years.

But to offset global warming caused by carbon emissions, an artificial shield against aerosol particles would have to be replenished continuously over decades, defeating a goal of the United Nations Framework Convention. on climate change to prevent “dangerous human interference with the climate system”. ”

If it stopped abruptly, the masking cooling effect of the protective aerosol cloud would quickly wane, allowing all the greenhouse gases accumulated in the atmosphere to hit the planet all at once. Global temperatures could suddenly soar four to six times faster than recent climate change, says a 2018 Yale study published in Nature Ecology & Evolution.

“How can we assure future generations that our governance systems are so robust that there will be no termination shock?” asked Gupta.

According to the political experts who published the open letter, an international consensus over several generations is simply not democratically feasible between all the governments of the world.

NOAA uses balloons like this one (shown being released in a photographic time lapse) to measure the size and number of aerosols in the stratosphere. Man-made aerosols are already causing major environmental problems on Earth, including the vast Asian Brown Cloud of air pollution, which has been linked to disruptions in the Asian monsoons. Photo by Patrick Cullis, CIRES/NOAA GML.

A journey from science fiction to real science

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 policy option of last resort, attracting attention and millions in funding.

In 2019, the United States Congress awarded the National Oceanic and Atmospheric Administration (NOAA) $4 million for solar geoengineering research. In March 2021, the National Academies of Sciences, Engineering, and Medicine of the United States called on the country to spend an additional sum $100-200 million. Billionaire Bill Gates made personal donations to world leader solar geoengineering research unit at Harvard University.

David Keith, one of the principal researchers leading the Solar Geoengineering Initiative and a professor of applied physics at Harvard, responded to the open letter, saying he shares concerns about uncertainty, moral hazard and governance challenges, but disagrees with a de facto permanent ban on solar power. geoengineering.

Aerosol pollution over eastern China. Increased use of coal and wood for winter heating across Asia often results in widespread haze, such as seen in this Moderate Resolution Imaging Spectroradiometer (MODIS) image taken by the Terra satellite on February 9, 2004 . Photo by Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC.

“It is difficult to justify a permanent non-use agreement on technology which – according to the literature and IPCC summaries [the UN Intergovernmental Panel on Climate Change] and the United States National Academy [of Science] – could significantly reduce climate risk,” Keith told Mongabay via email. “It seems like a stretch to suggest that we should block research into potentially useful technologies because the governance mechanisms are less than ideal.” He added that governance issues also arose with the mRNA technology responsible for several Covid-19 vaccines, and with the development of the internet, but none of these fears justified a permanent ban.

Last year, the Harvard team was forced to cancel its first outdoor geoengineering test, which was to be carried out in partnership with Sweden’s Space Corporation, following a Swedish public inquiry. expression led by the indigenous Sami people.

“You can model it and run experiments, but we can’t know the end effects of solar geoengineering on a planetary scale until after it’s deployed,” warned Frank Biermann, professor of global sustainability governance at the ‘University of Utrecht and one of the initiators of the letter, in a telephone. interview; he supported the Sami-led opposition to Harvard’s high-altitude test flight. “It’s an extremely risky proposition,” he concluded.

Air pollution particles, which are part of the Asian Brown Cloud, can travel around the globe and be distributed unevenly by winds with varying impacts. In April 2001, NASA satellites observed this massive swirling dust storm over China. The densest part of this aerosol cloud moved east over Japan, the Pacific Ocean and, within a week, towards the United States. Photo courtesy of NASA.

Read more: [Ministry For The Future]: Tackling the Climate Crisis in Science Fiction Style

Possible impacts on planetary boundaries

Solar geoengineering would reduce the amount of solar radiation reaching the planet’s surface and thus have profound effects. The planet would cool, but not uniformly. The Amazon region could become drier and warmeraccording to computer models, increasing the likelihood of major wildfires and increasing rainforest mortalityleading to a potential massive release of formerly sequestered carbon.

This huge release of carbon from the Amazon into the atmosphere would spell disaster for the planet, dramatically increasing global warming while reducing biodiversity. These impacts could end up being worse than the IPCC’s moderate climate change scenarios.

Depending on the type of aerosol particles used to form the shield, the deployment could also thin or add to the ozone layer, with unknown consequences. Without a strong reduction in carbon emissions, ocean acidification would continue to worsen.

Five fundamental measures that scientists say are necessary in an international agreement not to use solar geoengineering. Photo by the Solar Geoengineering Non-Use Agreement initiative.

Reducing solar radiation reaching the earth’s surface would also be counterproductive, thwarting solar power generation, one of the most promising alternatives to fossil fuels.

While proponents of solar geoengineering argue that this new technology can only be successful when accomplished alongside aggressive decarbonization, critics believe its deployment would undermine carbon reduction efforts. They argue that industry lobbyists, climate change deniers and some governments would politically weaponize a geoengineering solution, positioning it as a way to delay carbon regulation.

“The best option is to keep the genie in the bottle and not start with these very dangerous technologies,” Biermann said. “We need to focus not on these fantasies of non-existent technologies, but on the real problem at hand, which is decarbonization.”


Biermann, F., Oomen, J., Gupta, A., Ali, SH, Conca, K., Hajer, MA, … VanDeveer, SD (2022). Solar geoengineering: the case of an international non-use agreement. Wiley’s Interdisciplinary Reviews: Climate Change, e754. doi: 10.1002/wcc.754

Trisos, CH, Amatulli, G., Gurevitch, J. et al. Potentially dangerous consequences for biodiversity of implementing and stopping solar geoengineering. Nat Ecol Evol 2, 475–482 (2018). doi:10.1038/s41559-017-0431-0

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Banner image: A solar geoengineering technology test flight with a stratospheric balloon was planned by a Harvard research unit in partnership with the Swedish Space Corporation last year. It was postponed following public outcry. Photo by NASA/Goddard/BARREL.

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