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upstart writes:

Using a rail gun:

The wild concept was put forward by a group of astrophysicists in a study published Wednesday in PLOS Climate. Benjamin Bromley, Sameer Khan, and Scott Kenyon theorized that a solar shield could be created to deflect the sun's rays from Earth.

Coal and sea salt were considered as materials that could be used in the shield, helping to dim the sun by as much as 2%, or around six days of sunlight per year, thereby lowering the Earth's temperature. But lunar dust turned out to be the ideal candidate as it is just the right size and composition for efficiently scattering sunlight away from our planet, said Bromley.

Another advantage of moon dust is that it would take much less energy to launch it from the lunar surface compared to earth-based launches, though it would still require an estimated 22 billion pounds of dust to be mined and loaded into a ballistic device such as a rail gun and fired. This would need to be performed regularly to maintain the shield as the dust would slowly disperse. An abrupt halt in the cooling of the earth could caused "termination shock," in which the planet rapidly heats up, writes The Guardian.

[...] The proposal isn't the first time someone has suggested using a physical object in space to address global warming. A 1,250-mile glass shield, trillions of spacecraft sporting umbrella-like shields, blasting dust off an asteroid, a raft of thin-film silicon bubbles, and space mirrors are some of the other space-based suggestions. There was also the space shield in the magnificently awful Highlander 2.

[...] "Nothing should distract us from reducing greenhouse gas emissions here on Earth," said Bromley. "Our strategy may just be a moonshot, but we should explore all possibilities, in case we need more time to do the work here at home."

Journal Reference:
Bromley BC, Khan SH, Kenyon SJ (2023) Dust as a solar shield. PLOS Clim 2(2): e0000133. https://doi.org/10.1371/journal.pclm.0000133

Original Submission