Launching a huge dust cloud from the moon could ease global warming

Launching a dust cloud from the moon to block sunlight reaching Earth could reduce global warming, but such a strategy may require more than a decade’s worth of research before it can be implemented. The risks involved with such an approach in terms of how it could affect agriculture, ecosystems and water quality in different parts of the world are also unclear.

Placing more than 100 million tonnes of dust between Earth and the sun to partially block light from reaching our planet has previously been explored as a way to combat climate change. Such dust particles would shade Earth by absorbing light energy or scattering light particles, known as photons, away from Earth.

To achieve this, the dust would need to be placed 1.5 million kilometres from Earth, where the gravitational pull of the sun and our planet cancel out. Here, objects stay at a fixed position known as the first Lagrange point, or L1.

Different research groups have explored placing dust at L1, but energy from photons and charged particles ejected from the sun, known as the solar wind, can gradually nudge dust further away from its desired position, which would need correcting.

Now, after running thousands of computer simulations, Benjamin Bromley at the University of Utah and his colleagues have found that continuously launching a stream of lunar dust directly from the moon’s north pole towards L1 at a speed of 2.8 kilometres per second may be a better approach.

In this scenario, the simulations suggest that each propelled dust particle spends about five days blocking Earth-bound sunlight, before dispersing throughout the solar system.

Considering the gravitational pull of the sun, Earth and other planets, as well as non-gravitational forces such as the solar wind, the simulations found that maintaining a dust shield with a mass of 1 million tonnes near L1 for a year could dim sunlight across Earth by 1.8 per cent, equivalent to completely blocking six days of sunlight.

If the approach were sustained indefinitely, or until other measures were introduced to remove carbon dioxide from Earth’s atmosphere, this could offset the rise in carbon dioxide levels that has occurred since the industrial revolution, says Ben Kravitz at Indiana University, Bloomington.

“If this method works, it would certainly be effective at reducing global temperature, but it’s hard to say whether it would be worth it relative to the effort and resources used,” he says.

While the simulations didn’t model the use of any machinery to launch the lunar dust towards L1, you could use a railgun, which propels things via electromagnetic energy, says Bromley. “This would be perfect because it could be fueled by a few square kilometres of solar panels placed near the launch site,” he says.

However, shading the entire Earth will have unequal effects in different regions, says Kravitz. “Temperature, precipitation, winds and many other things will change [as a result of this strategy], and they will change differently in different places,” he says. “Those changes will, of course, translate into effects on agriculture, ecosystems and water quality.”

Before a strategy like this can be implemented, large-scale engineering studies need to be carried out by multiple agencies in different countries and with consideration by the United Nations, says Curtis Struck at Iowa State University.

Another issue is that there would probably be inaccuracies in the launch and scattering of the dust, which would have unknown effects. “Would there be enhanced micrometeorite falls to Earth and damage to Earth-orbiting satellites?” says Struck. “This and many other questions have not been studied in the necessary detail.”

Furthermore, considering an approach like this shouldn’t replace our efforts to decrease carbon emissions on Earth. “We have to keep reducing the greenhouse gases within our own atmosphere, no matter what,” says Bromley. “Our dust shield solution would simply buy us more time.”