A new climate solution involves shooting moon dust into space to create a 'solar shield' around Earth, but scientists say it's a risky last resort

• Three astrophysicists discovered that lunar dust is just the right size to block the sun's rays.
• Shooting 11 million tons of moon dust into space could create a solar shield to cool Earth, they say.

Three astrophysicists have an out-of-this-world solution for the climate crisis — mining dust from the moon and shooting it into space between Earth and the sun.

Researchers Benjamin Bromley, Sameer Khan, and Scott Kenyon say they've found that dust grains from the moon could be the right size to scatter sunlight and shield Earth from solar radiation, per a paper published on Wednesday in the peer-reviewed journal PLOS.

If humans mine dust from the moon and shoot it into space, so that it settles about 1 million miles away from Earth, between our planet and the sun, that would obscure the sun's rays by 1.8% — or around six days of sunlight per year — and lower the Earth's temperature, the researchers calculated.

This moonshot solution is the latest in a series of ideas for blocking solar radiation to cool Earth. Other proposals include spraying aerosols into the stratosphere, or injecting sea salt into clouds above the ocean to make them brighter.

These hypothetical schemes to block the sun — sometimes called "geoengineering" — aim to counteract the warming that humans' greenhouse-gas emissions have caused, thereby reducing catastrophic consequences like severe weather and water scarcity.

However, many climate experts view geoengineering as a last resort, since it could have unintended consequences that scientists don't fully understand. Last year, hundreds of scientists signed an open letter asking world governments to pledge not to use solar geoengineering.

"While it is certainly true that reducing sunlight can cause cooling, it acts on a very different part of the climate system than carbon dioxide," Michael Mann, a a climate scientist at the University of Pennsylvania, told The Hill in response to the moonshot study.

"Efforts to offset carbon dioxide-caused warming with sunlight reduction would yield a very different climate, perhaps one unlike any seen before in Earth's history, with massive shifts in atmospheric circulation and rainfall patterns and possible worsening of droughts," he added.

Geoengineering could be a distraction, too. Overwhelmingly, scientists say the main way to solve the climate crisis is to drastically cut emissions of heat-trapping gases.

Bromley, a professor from the physics and astronomy department at the University of Utah, and the project's lead researcher, is in agreement.

"I hope that humans can work together here at home to reduce greenhouse gases that trap the sun's energy so that something like this is not needed. But if we need more time, our idea could become important," he told Insider in an email.

Cannon-balling 11 million tons of moon dust into space

Humans would need around 11 million tons of moon dust to create an effective enough "solar shield," the researchers estimated.

The cheapest plan would involve launching the dust from the moon's surface, instead of Earth's, because it would take much less energy to eject the moon dust from there.

The proposal involves shooting the dust into space with ballistics, meaning rockets aren't needed, Bromley said. Some of the technology to create the dust shield already exists, like dust scattering and mining, he added.

"Once dust is released, its only impact is to shade Earth. It will not otherwise interact with our planet again," Bromley and his team wrote.

That means the dust shield could have no long-term impact on Earth's atmosphere, compared to many other Earth-based strategies to block solar radiation, they wrote.

However, the grains of moon dust would eventually start drifting out of position, and humans would need to keep firing bursts of moon dust to replenish the shield's strength, the scientists wrote.

The real solution is simpler than mining the moon

Bromley told The Guardian that his team's idea shouldn't take the focus away from the primary climate goal of reducing emissions to stop the planet from heating up.

"Nothing should distract us from reducing greenhouse gas emissions here on Earth," he said, per The Guardian.

Frank Biermann, a professor of global sustainability governance at Utrecht University, told The Guardian he thinks "mining the moon is not the answer that we need."

"The idea to mine the moon or near-Earth asteroids in order to artificially block parts of the sunlight is no solution to the ongoing and intensifying climate crisis," he said, per The Guardian.

Other research is still exploring other ways to divert the sun's rays. In 2022, the White House launched a five-year plan to assess options involving "solar and other rapid climate interventions" to deal with the crisis.

A group of Harvard researchers has also been researching the effectiveness of spraying tiny particles into the stratosphere to reflect the sun's rays and reduce the impact of global warming. The project, known as SCoPEx, has Bill Gates' financial backing.

February 10, 2023: This story has been updated with comments from Bromley.