Tens of thousands of satellites can cool the earth with a sunscreen

Read a special on geoengineering from 2020: We can also carve the climate

Space based geo-engineering of these technologies the most sounds like science fiction. Or like the plot of a villainous movie. During a brainstorming afternoon in 2019, Tomas Hamann and some colleagues at the German space technology company OHB listed 23 ideas for blocking solar radiation, from ‘space confetti’ – flakes in a spot between the sun and the earth – to ‘space trees’ – organically growing structures between sun and earth.

Some ideas were really crap

Tomas Hamann technology company OHB

One by one they shot those ideas off again. “Some were really crap,” says Hamann. “But from others I really expected it to work. The mechanical crushing of an asteroid that had been dragged to a certain point between the sun and Earth, for example. The cloud of dust would block the sun’s rays. But a little more research showed that grit particles can cause dangerous space debris.” He found another interesting idea a ring of particles around the Earth, such as the rings around Saturn. “A spectacular picture, but it could cause local temperature changes of 6 to 7 degrees on average. That would have huge effects, so a very bad idea. The ring would also have lit up at night, so it would never really get dark again.”

One idea stuck: a fleet of small satellites that all unfold a sail and together form a shade cloth. The fleet would fly in a formation at a specific spot between the sun and Earth: Lagrangian Point 1 (L1). “That’s a semi-stable point between the sun and the earth,” says Hamann. “You can more or less park satellites there. That makes it a perfect place to build a sun shield. In other places, the shield wouldn’t be between the sun and Earth most of the time.” You wouldn’t see it from Earth.

“Just to be clear, we are not at all in favor of doing something like that,” says Hamann. „Full commitment to emission reduction is plan A, plan B is the extraction of CO₂ from the sky. Reducing radiation is the last straw.” During the exploration he did with his colleagues, it turned out that other options for reducing radiation also seem much more feasible. Injecting particles into the stratosphere is cheaper and more feasible. “But setting up a space project takes about ten years. If you don’t investigate now, you’ll be too late anyway.”

That research belongs to scientists, Hamann believes. “We initiated this consortium because we want to promote the research. Geo-engineering has major consequences, climatologically, but also ethically and economically. That must have a solid scientific basis.” Scientists from the universities involved now meet monthly, and each contribute ideas about the fleet of sunshade satellites based on their specialism.

Paper-thin mirror

In Delft, for example, research is being conducted into solar sails. “Solar sails are a new way to propel satellites,” says Jeannette Heiligers, assistant professor at TU Delft. “Normally, fuel is needed to fly satellites. A shade sail is a large, wafer-thin transom. The photons from the sunlight that fall on that mirror give pressure. It’s a very small force, but because there’s no drag in space, it’s enough to move.” It is a sustainable way of propulsion.

There have now been four successful missions with a solar sail, says Heiligers. ‘Three around the earth to show that such a sail can be properly launched and unfolded and that it can be used to make speed. And one mission has gone to Venus, to show that course can be changed too.” Heiligers is now working on a NASA satellite with an 80 square meter solar sail. “It fits folded into a satellite the size of two loaves of bread.”

In addition to being a means of propulsion, the sails could also function as a shade cloth. “To block 1 to 2 percent of the sunlight you would need about 6 million square kilometers of solar sails. An area roughly the size of mainland Europe,” says Heiligers. “So it concerns a lot of satellites.”

The biggest challenge is therefore not designing the satellites, believes Heiligers. “It’s the scale. There should be a production line that is perhaps larger than the car industry. Where should you do that? Here on earth seems logical, but then everything has to be launched – with the associated emissions. Can it also be done on site in space?” This is also being considered in the consortium.

Equator and Poland

How the satellites should fly, in what formation and where exactly, are other questions Heiligers is happy to help answer. “I am also involved in orbit mechanics, simulating and calculating how objects move in space.” Whether the entire fleet should fly around the L1 point remains to be seen. “It’s an attractive option. If you hang a shade cloth there, you reduce the sunlight by 1 to 2 percent over the entire half of the earth that faces the sun,” says Heiligers. “But maybe it’s better to have less shadow around the equator and more shadow around the poles. Fellow researchers think that it is therefore better to put some of the satellites in orbit around the Earth, then you have more control over where the shadow falls and a more differentiated effect.”

Suppose it all works. What will happen to the Earth’s climate then? “That is very roughly clear,” says Claudia Wieners, climate scientist at Utrecht University and also involved in the consortium. “Funny enough, the first model experiments that calculated what happens if you lower the temperature on Earth, based on ‘dimming the sun a bit’. That was then, about 15 years ago, not with the idea that it could ever be possible, but because it was a manageable variable.” The earth is cooling, that’s for sure. If you do it homogeneously, 1 to 2 percent less solar radiation arrives everywhere. “But then you are not just back in a situation as it was. Because air and ocean currents transfer heat from the equator to the poles, the poles warm up relatively more thanks to the greenhouse effect than you would expect based on their meager insolation.” It is also clear that there is more to it than just the temperature. “With regard to precipitation, for example, you see that it will become drier globally, locally you could get very heavy precipitation.”

Climate models have become much more sophisticated since those early days, although the uncertainties remain high. “For example, it is unclear what geoengineering does to sea level rise,” says Wieners. “In Greenland, a lot of ice is melting due to sunlight and warm air. But Antarctica is melting from below, warming seawater is coming into contact with the ice there. Global cooling is also good for seawater, but how quickly does it react? Is that in time to stop Antarctica from melting? And maybe due to the cooling, the flow patterns worldwide will change, what happens then?”

The genie is long out of the bottle!

Claudia Wieners climate scientist

“The first knowledge is there, but much is not yet well understood,” says Wieners. She is a strong supporter of much more research into geoengineering. “We need to have more insight into what can work, and especially into what doesn’t work. Some want to hold back research, so as not to be tempted to use geoengineering. But the genie is long out of the bottle! And what if in 30 years it turns out that CO₂reduction alone was not enough, for example because even 1.5 degrees of warming is already disastrous? You must be able to come up with substantiated arguments if the question about deploying geoengineering actually comes up.”