The idea of manually tampering with our atmosphere to combat climate change, such as by seeding clouds with reflective particles to dim the Sun, remains extremely controversial. These acts of geoengineering could deliver us from climate doom, the thinking goes, or backfire spectacularly in ways we never anticipated — which is why scientists are proceeding with caution.

But to an extent, something like this is already happening on a global scale. In a new study published in the journal Earth’s Future, researchers warn that the air pollution caused by satellites burning up in the Earth’s atmosphere is already decreasing the amount of sunlight reaching the Earth’s surface. And if the space industry continues growing at its current pace, the impact could eventually become significant enough to alter the entire climate.

Project lead and coauthor Eloise Marais, a professor of atmospheric chemistry and air quality at University College London, laid out the stakes in a striking comparison: “The space industry pollution is like a small-scale, unregulated geoengineering experiment that could have many unintended and serious environmental consequences,” she warned in a statement about the work.

Space launches have accelerated in the past decade and have tripled in the past five years, spearheaded by companies like Elon Musk’s SpaceX. A good chunk of the launches are to bring satellites into the Earth’s orbit. SpaceX’s Starlink internet service boasts nearly 12,000 of them (and Musk wants to launch a million more). These huge networks are referred to as megaconstellations, signaling a new paradigm in how satellites are used and deployed. Competitors are racing to build their own megaconstellations, including Jeff Bezos’ Blue Origin, which plans to deploy over 5,000 satellites.

These satellites are expendable. They’re designed to deorbit after a few years and then burn up — harmlessly, we’re told — in the Earth’s atmosphere, and constantly need to be replenished. But scientists have begun paying closer attention to the environmental impact of treating the atmosphere like a crematorium for satellites, with early studies finding that they release metals like lead and aluminum. Other research has raised the ominous possibility that some of these metal pollutants could trigger a chain reaction that lays waste to the ozone.

In this latest work, the researchers modeled the major pollutants from de-orbited megaconstellation satellites between 2020 and 2022. In 2020, the satellites accounted for 25 percent of the total climate impact from the space industry and will climb to 42 percent by 2029. By that same year, they project that the accumulated pollutants released by burning satellites will produce similar effects to solar geoengineering strategies, like aerosol injection.

The researchers also mapped the impact of rocket launches, which release soot particles. Once released in the upper atmosphere, the soot stays there for years, unlike soot released from the ground, which gets washed away by rainfall. By 2029, rocket launches will emit about 870 metric tons into the atmosphere annually, which is roughly equal to the total soot emissions from passenger cars in the UK, a release notes.

“Currently the impact on the atmosphere is small, so we still have the chance to act early before it becomes a more serious issue that is harder to reverse or repair,” Marais said in the statement. “So far there has been limited effort to effectively regulate this type of pollution.”

“The cooling effect from the reduction in sunlight that we calculate with our models may sound like a welcome change against the backdrop of global warming,” she added, “but we need to be extremely cautious.”

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