Could massive solar shields in space stop global warming?

Some astronomers argue that reducing the amount of solar radiation reaching Earth by blocking sunlight in space is safer than changing Earth’s atmosphere. Credit: Marek Piwnicki/Unsplash

After a summer record of global weather disasters, climate change is a hot topic. But while many look to the sky in despair, some astronomers do so with hope. They see the L1 Lagrange point — the farthest point between Earth and the Sun where gravity is perfectly balanced — as a potential ally in fighting climate change.

Two recent papers propose using L1, about 1 million miles (1.6 million kilometers) from Earth, to reduce global warming. Both proposals, while purely theoretical, are based on space-based ideas known as solar geoengineering, a family of technologies that artificially control how much the sun heats our planet. One Paper Proposes a giant sail in space Others uses lunar dust, but both rely on a gravitational balancing act to hold the shield.

The concept of geoengineering has long been controversial, and solutions involving space-powered hardware are particularly ambitious. Critics say space-based geoengineering is a distraction from reducing carbon emissions and won’t be technically feasible for years — too long to wait for climate action. But space-based solutions have many advantages compared to Earth-based geoengineering projects, at least in principle. As droughts, wildfires, and floods ravage regions around the world, few scientists are more willing to consider this model.

István Sabuti of the University of Hawaii in Honolulu and an author of the paper also says that radical solutions are needed. A week after his article was published in late July, a tragic wildfire swept through West Maui and destroyed the town of Lahaina.

„These are the extremes that climate scientists are warning us about, otherwise it’s highly unlikely,” Shabudi says. „Lahaina strengthens my resolve to continue this research and try to contribute as much as I can toward a solution.”

Lighting up a shield

Szapudi’s solution involves an asteroid, space tethers and a giant graphene sail. The asteroid will be positioned closer to the Sun than the L1 point and bound at a wider distance to the shield positioned closer to Earth on the other side of L1.

The tug between the two—the asteroid falling toward the Sun and the sail pushed toward Earth by the solar wind—keeps the Earth-Sun pair in balance. Shabudi’s paper notes that if the shield sits closer to Earth, its shadow will be larger, so it should be smaller. This would allow for a lighter payload, but would require longer tethers between the asteroid and the shield.

The magazine was published on July 31 Proceedings of the National Academy of Sciences.

As a purely conceptual paper, Szabudi’s equations do not specify the area of ​​the shield or the mass of the asteroid, but his other numbers are ominous.

He proposes various tethers of 1 million miles (1.6 million km), four times the distance between Earth and the Moon, and an armored-tether payload of 35,000 tons. SpaceX is the largest lift rocket available StarshipCarrying a maximum payload of 166 tonnes, more than 200 launches would be required to assemble the system.

„SpaceX already launches every four days,” Szapudi says, „and they’re increasing their frequency. For a year, you’ll put one payload a day.

As for picking up and moving the asteroid, his ideas have a Hawaiian bent: like any good surfer, he uses the shield as a paddle to alter the asteroid’s path. „First we find the ideal asteroid, and then we maneuver it like a kite surfer, pulling it like strings,” Sabudi explains.

Gathering clouds

Planning and assembling the shield system could take decades, but climate scientists say they can’t spare time. Another team of astronomers has a low-tech solution that could take off once NASA’s lunar program lands. They propose using lunar dust to shadow the Earth, and their paper contains many innovations and surprises.

„You don’t need to use L1 to stop your stuff,” says Benjamin Bromley of the University of Utah, in a paper published earlier this year. PLOS Climate.

„One strategy is to find orbits that actually intercept the Earth-Sun line of sight. You can tune them so that dust stays in this special orbit toward L1 for days. It wasn’t clear to us when we started that there were such orbits where you could actually have something between the Earth and the Sun that wasn’t at L1.

Bromley and his team borrowed from their knowledge of how these rings of debris obscure starlight in the background of studying rings of exoplanet-forming dust, called protoplanetary discs, that orbit stars. They analyzed different materials that provide the best sun shading based on grain size, mass and light scattering.

The correct material, it turns out, is the abundant silica regolith that covers the Moon. Propelling it into space requires only solar energy, another abundant lunar resource. The team proposes using solar-powered electromagnetic railguns to eject dust from the Moon’s surface toward the L1 Lagrange point. Momentum and gravity will do the rest.

He emphasizes that the system is easily reversible. As the Earth moves through space, the lunar dust fraction disperses and travels harmlessly behind us along with the solar wind.

„It’s an advantage and a disadvantage,” Bromley says, adding that the dust shield needs to be constantly replenished with its 11 million tons of lunar regolith. „But if you want to get back to where you were before you started, there’s nothing you have to do.”

Space versus Earth

Such resiliency is a key issue for those fundamentally opposed to geoengineering. Some climate scientists worry that Earth-based geoengineering ideas — such as injecting aerosols into the stratosphere to deflect solar radiation or pouring iron into the oceans to increase carbon dioxide absorption — could have disproportionate and unintended consequences.

More than 400 educators have signed Letter Petitioning the United Nations and others to „block the normalization of solar geoengineering as a climate policy option.” This discussion is a split The climate science community and institutions such as Bill Gates and the National Academies of Sciences, Engineering and Medicine consider space-based solutions to be too benign. Solar Engineering Research Program of Harvard University Website The opposition says that space-based proposals are too far-fetched, if not too far-fetched.

Meanwhile, the UN says its ideal target of 1.5 degrees Celsius (measured against pre-industrial levels) of maximum global temperature rise must be reached this decade.

„The solution to global warming is to move quickly to a wind- and solar-powered economy and leave fossil fuels in the ground,” said Alan Robock, a climatologist at Rutgers University. Astronomy In an email. „We need to do research on the impacts of the various proposed climate intervention programs … but there is [presently] The technology for solar radiation conversion does not exist, and will not for at least another decade.

With temperatures already 1.1 degrees Celsius above pre-1800 temperatures, almost all scientists agree that something must be done sooner, whatever the cost.

„Our proposal would be very expensive, and I think it would require cooperation, and it’s fair to say we put carbon in the ground instead. Maybe it will become a requirement, but I really hope not.”