Yes, the idea sounds like science fiction. Yes, it would require (a lot of) new engineering. Yes, there are more feasible climate mitigation tactics that can be employed now and in the near future. But the researchers view this rigorous physics experiment as a backup option that could aid — not replace — existing strategies to help humankind live on a more comfortable Earth.
“We cannot as humanity let go of our primary goal of reducing greenhouse gas emissions here on our planet. That’s got to be the first job,” said Ben Bromley, the study’s lead author and an astrophysicist at University of Utah. “Our idea is one — and it’s a very, very intensive one — to contribute to climate change mitigation, if we need more time here at home.”
The astrophysicists came up with a space dust shield by borrowing concepts from their usual research focused on how planets form around distant stars. Bromley explained that planets form through a messy process involving a lot of collisions, which kick up dust that can intercept a large amount of starlight. So why not explore strategically using such light-blocking dust for Earth’s benefit?
“The literature around space-based geoengineering now spans more than three decades and is filled with creative, often outlandish ideas,” Chad M. Baum, a behavioral scientist at Aarhus University who was not involved in the new study, said in an email. “Some have claimed that seeing these kinds of climate solutions being discussed might bring home the urgency of the situation we are in.”
For instance, the amount of material needed to actually shade the sun exceeds 10 billion kilograms (22 billion pounds), which is about 100 times more mass than humans have ever sent into space. Bromley says dust is very efficient at scattering sunlight relative to its size. The team considered different types of dust, scattering properties and size. The team found that aggregates of fluffy and highly porous particles scattered light the best, but they opted for a particle perhaps more easily accessible in space: moon dust.
In one computer simulation, the team shot lunar dust from the moon’s surface toward the sun. Bromley said the device to launch the lunar dust into space could be something similar to an electromagnetic gun, cannon or rocket — picture a T-shirt cannon sending dust into orbit. In the simulation, the dust scattered along various routes until the team found suitable trajectories, which allowed the dust to concentrate temporarily and act as a sun shield. Bromley said the dust would periodically disperse away from Earth and throughout the solar system.
In another simulation, the team shot off dust from a space platform about 1 million miles from Earth. This would be in an area known as L1 (Lagrange point 1), where objects tend to stay put because of equal gravitational pulls between the sun and Earth. This idea required more astronomical cost and effort because they would need a space platform and a dust supply that could be easily replenished.
Baum doesn’t normally find dust clouds to be among the most interesting climate solutions, but he thinks the authors “did an admirable job considering many of the different permutations of a potential approach, and specifically looking at the potential orbits.”
But he points out issues with the sheer amount of material required — 10 billion kilograms of dust — which the authors say may need to be replaced every few days after the dust streams float away. Also, he anticipates many would take issue with how much “moon engineering” would be required to make the idea work.
“We haven’t solved the climate change problem yet, so these novel ideas are great [for] eliciting reactions from both the public and scientific community,” Yonekura, a scientist at the Rand Corp., said in an email. “Solar geoengineering — though highly controversial — does not seem to be off the table, and these new solution ideas help provide alternative approaches that weigh differently in a cost-benefit analysis.”
“Global climate change from human injections of greenhouse gases is a real problem, but there is a much simpler, safer, and cheaper solution: leave the fossil fuels in the ground and run the world on solar and wind power, of which there is enough to supply power for everyone,” said Robock, a professor of climate science at Rutgers University who was an author on the 2007 Intergovernmental Panel on Climate Change committee that was awarded the Nobel Peace Prize.
In terms of “climate intervention” projects, Robock said there are a number of more realistic proposals that should receive additional attention. He said carbon-dioxide removal will probably be useful in the future, but is currently expensive and raises potential environmental questions, such as where to bury the carbon. Robock also said more research is needed even with injecting aerosols into atmosphere, even though it is often discussed as a realistic possibility.
“We’re coming in this as people who certainly care about the Earth, care about life here,” said Bromley. “I don’t know what path people will take, but if [space dust] is one that we view as being more practical, better for humanity, I would love to see this put into operation. It is fascinating.”