CLIMATEWIRE | Some scientists imagine that a gigantic shield could be placed in space to block the sun’s rays and lower temperatures on Earth.

It’s just an idea for now — one that’s been floating at the fringes of climate geoengineering conversations for at least 30 years. But a scientific study released Monday has renewed interest in the concept — and suggests that it might actually work.

The idea is simple in theory. A giant, reflective sunshade, constructed in space between the Earth and the sun, could block a small amount of incoming solar radiation and help cool the planet.

Scientists have already located the ideal place to put it — a kind of sweet spot in space where the competing forces of the Earth’s gravity, the sun’s gravity and the sun’s radiation balance out. Known as the L1 Lagrange point, it’s where objects in space wouldn’t get jostled around too much.

But there’s a catch.

Even in L1, the sunshade would need to have a certain critical mass to avoid being shoved out of place — at least a few million metric tons. It could be prohibitively expensive, time-consuming and difficult to transport and assemble that much material in space. (For reference, the Hoover Dam weighs 6.6 million tons.)

But theoretical cosmologist István Szapudi, a scientist at the University of Hawaii, has come up with an alternative idea that was published Monday in the journal Proceedings of the National Academy of Sciences.

It’s possible to construct a much smaller shield, he said, and then tether it to a heavy counterweight to solve the mass problem. In theory, the counterweight could be an object already floating in space, like an asteroid or some other space debris.

Previous studies have suggested that a sunshade would need to block out about 1.7 percent of incoming solar radiation to lower the Earth’s temperature enough to meet the targets of the Paris climate agreement. With that figure in mind, and a sufficient counterweight, Szapudi calculates that a sunshade could be as light as 35,000 metric tons.

Szapudi said his typical research field doesn’t include climate geoengineering. But during the pandemic, he happened to collaborate with other researchers on papers about Covid-19 economics and epidemiology. It changed his perspective.

“I got the taste of trying to do something that helps to solve problems,” Szapudi said. “And climate change is one of the biggest problems facing humanity.”

The concept of a giant floating sunshade may sound like a plotline from a science fiction novel — and, for now, it’s barely more than that. The new paper is simply a concept study, according to Szapudi, mathematically suggesting that the basic idea could work.

It would take “an army of engineers” to actually prove it’s feasible in real life, he said.

Interest in climate geoengineering — also known as solar radiation modification — is on the rise as the planet’s temperatures continue to climb. But space-based geoengineering concepts, in general, have gotten less attention than other proposals.

The most widely discussed geoengineering concept is tethered to Earth, not out in space. Scientists have suggested that spraying reflective aerosols into the Earth’s atmosphere could help beam incoming sunlight away from the planet, lowering temperatures in the process.

For now, it’s also just an idea — but it’s gaining attention. Numerous studies in recent years have attempted to investigate its possible side effects. Some scientists have also proposed small field experiments to begin testing out the theory.

But it’s highly controversial. Studies have suggested that solar geoengineering could come with an array of unintended consequences, including negative effects on precipitation and other weather patterns around the world and possible damage to the Earth’s ozone layer.

And once begun, solar geoengineering would be difficult to safely stop, experts say. If the practice began and suddenly halted, the Earth’s temperatures could skyrocket at life-threatening speed, a phenomenon scientists have dubbed “terminal shock.”

These possibilities have prompted calls among scientists and policy experts for stringent international guidelines when it comes to geoengineering research.

At the same time, increased research on solar geoengineering is also gaining cautious support.

In 2021, a report from the National Academies of Sciences, Engineering and Medicine concluded that solar geoengineering deserves more research — as long as it’s carefully regulated. Then, in June, a White House report also indicated that the Biden administration is open to further research on the subject, although it added that there are currently no plans to establish a comprehensive research program.

Both of these reports focused on the most mainstream solar geoengineering proposal, involving aerosols sprayed into the atmosphere. The White House report notes that it considers only atmospheric approaches to the issue and “does not consider space-based approaches” at all.

Still, a wide variety of other geoengineering proposals — some more outlandish than others — have continued to pop up in scientific and public discussions.

Scientists have proposed various ways to refreeze the Arctic, like stabilizing glaciers with giant underwater ridges or using reflective materials to shore up Arctic sea ice. (The latter, experts have recently warned, could do more harm than good.)

The concept of a giant sunshade isn’t the only space-based geoengineering proposal floating around. A paper published in February suggested it may be possible to cool the Earth by shooting large volumes of sun-obscuring moon dust — using a cannon literally placed on the surface of the moon — into space.

The sunshade idea is one of the older proposals. Engineer James Early first suggested it in 1989, when he claimed that a giant glass shield could help deflect sunlight away from Earth. It’s cropped back up in various papers, and in different forms, in the decades since.

Because these methods are even less studied than the controversial atmospheric aerosol idea, potential side effects are less certain. Critics of geoengineering — in all of its forms — frequently argue that such proposals are not only risky, but may undermine global efforts to reduce greenhouse gas emissions.

But new ideas keep coming.

Szapudi, the author of the new sunshade study, acknowledges that geoengineering isn’t a replacement for cutting emissions. But he also argues that it’s better to investigate all possible tools in the climate arsenal.

“This is a big problem,” he said. “And we should look at all possible solutions and work towards mitigating the climate change by any and all means.”

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2023. E&E News provides essential news for energy and environment professionals.