Researchers say that a ‘planetary sunshade’ placed between Earth and the Sun could cool down the planet by 1 °C.Credit: Mongpro/Getty
In August, entrepreneur Elon Musk suggested in a social-media post that Earth could be cooled by launching satellites into space to shade the planet from the Sun. These “sentient satellites”, he wrote, “can solve global warming for ~1B years”.
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It’s unclear whether Musk, the chief executive of aerospace firm SpaceX in Starbase, Texas, meant for this to be taken seriously. But some researchers are earnestly investigating space-based methods of reflecting sunlight away from Earth to cool the planet as temperatures rise to increasingly dangerous levels.
A non-profit organization called the Planetary Sunshade Institute in Los Angeles, California, published a report this month that researchers say is the most detailed analysis yet of such geoengineering methods. The report — which summarizes studies from a consortium of engineers and climate scientists, including some from leading space agencies such as NASA — estimates that it could become viable to begin building a ‘planetary sunshade’ in as few as 20–40 years. The timeline would depend on the rate at which heavy-lift rockets are developed that can haul millions of tonnes of material into deep space to create the sunshade. (SpaceX, which is not involved in the report, did not respond to a query from Nature about whether it is conducting research on this topic.)
A lot of people think this idea is “just fantasy”, says Chantal Cappelletti, a space-systems engineer at the University of Nottingham, UK, who is part of the consortium. But the falling cost of space launches have made the prospect seem more feasible, she says.
Not so science fiction
Blocking sunlight to cool the planet through solar geoengineering has long been controversial. Proposals have included releasing sunlight-reflecting particles into Earth’s atmosphere, which could affect the planet in poorly understood ways, such as disrupting precipitation and plant growth. Space-based approaches could come with unique risks, including the pollution unleashed from many thousands of rocket launches. Critics also say that focusing attention on geoengineering distracts from the urgent need to cut greenhouse-gas emissions to address climate change.
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But solar geoengineering has received more attention from researchers as Earth looks set to hurtle past 1.5 °C of warming above the planet’s pre-industrial baseline temperature. The “accelerating climate crisis” is pushing the world towards solar geoengineering, says Morgan Goodwin, a climate activist and executive director of the Planetary Sunshade Institute.
The report is the group’s biggest project so far, funded by a £400,000 (US$530,000) grant from the UK Advanced Research and Invention Agency (ARIA), a body sponsored by the government to fund high-risk, high-reward research. That grant is part of a larger £56.8-million ARIA research programme on solar geoengineering.
Daniele Visioni, a climate scientist at Cornell University in Ithaca, New York, says that he had previously dismissed space-based approaches as science fiction. But after attending an engineering workshop on such approaches earlier this year, he was persuaded that they deserve more attention. However, “I still wouldn’t put this as something feasible before the end of the century”, he says.
Between Earth and the Sun