Rocket launches are turning the upper atmosphere into an accidental climate experiment

A new study finds pollution from satellite megaconstellations could account for 42% of the space sector’s climate impact by 2029.

For most of the space age, rocket launches were rare. Their environmental impact was also negligible. A plume here, a plume there, nothing too damaging. The pollution they left behind was incomparably small compared with cars, power plants and heavy industry.

That is changing fast.

A new study led by researchers at University College London (UCL) finds that pollution from satellite “megaconstellations” (vast networks of internet satellites launched in batches) is accumulating in the upper atmosphere. By 2029, these systems could account for 42% of the total climate impact from space-sector pollution, even though the megaconstellation boom is only a few years old.

Soot in space

The international, multi-organizational study published in Earth’s Future, looked at pollution from rocket launches, discarded rocket bodies and dead satellites burning up during reentry. The researchers modeled emissions from 2020 to 2022, then projected how those emissions could grow through the end of the decade.

Their main concern is black carbon, better known as soot.

On Earth’s surface, soot from cars or factories doesn’t stay in the air forever as rain and weather systems help wash it out. But rockets inject soot much higher, into parts of the atmosphere where air moves slowly and cleanup is much harder. There, particles can linger for years. That makes rocket soot strangely potent. According to the study, soot released by launches can be about 540 times more effective at altering the climate than soot emitted near the surface.

“Rocket launches are a unique source of pollution,” said lead author Connor Barker of UCL Geography. He said they inject chemicals directly into upper atmospheric layers, reaching what he described as one of Earth’s last relatively pristine environments.

The effect isn’t just simple warming. The researchers found that soot from rocket launches can slightly cool Earth’s surface by blocking a small amount of sunlight. That might sound useful in a warming climate, but the scientists warn against treating it as good news.

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This is a climate experiment

Eloise Marais, professor at UCL Geography and project lead, called it a “small-scale, unregulated geoengineering experiment that could have many unintended and serious environmental consequences.”

Geoengineering usually refers to deliberate attempts to cool the planet, such as adding particles to the stratosphere to reflect sunlight. In this case, it’s not deliberate; it’s an accidental side effect of a space industry launching more often, more cheaply and at far greater scale.

Basically, rocket soot can slightly cool Earth’s surface while warming parts of the upper atmosphere where the particles linger. But Marais said that while cooling “may sound like a welcome change,” we need to be “extremely cautious” about something like this.

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“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,” she said. “So far there has been limited effort to effectively regulate this type of pollution.”

More satellites

The main driver behind this is the rise of megaconstellations. SpaceX’s Starlink is the best known, with over 10,000 of satellites already in orbit. Other networks are growing or planned, including Amazon’s Project Kuiper and China’s Guowang constellation. These systems promise broadband internet across wide areas, including remote regions. But they also depend on frequent launches and regular satellite replacement.

That launch cadence is rising sharply. UCL said that annual rocket launches nearly tripled from 114 in 2020 to 329 in 2025, driven largely by SpaceX’s Falcon 9 rockets. Falcon 9 uses kerosene-based fuel, which produces soot during launch.

The study estimates that by 2029, the space industry could release about 870 tonnes of soot into the atmosphere each year. That is roughly comparable to the soot emitted annually by all passenger cars in the United Kingdom, according to the report.

Not all doom and gloom

The researchers also looked at ozone. Rockets and reentering spacecraft can release chemicals and particles that alter ozone chemistry. The ozone layer protects life on Earth from harmful ultraviolet radiation, so even small changes matter.

For now, the ozone effect from megaconstellations appears to be small in the grand scheme of things. By 2029, all rocket launches together are projected to deplete global ozone by about 0.02%, far below the roughly 2% ozone loss linked to substances regulated under the Montreal Protocol.

That doesn’t mean the risk can be ignored. The researchers say their projections may already be too conservative. They based them on launch trends from 2020 to 2022, but launch numbers from 2023 to 2025 have already surpassed those early estimates.

The broader point isn’t that rockets are now a climate threat on the scale of fossil fuels. They are not. The space sector remains much smaller than major industrial sources of greenhouse gases. Rather, the concern is where the pollution actually goes. Rockets do not just add exhaust to the air people breathe. They deliver soot and chemicals straight into high atmospheric layers, where small amounts can have larger effects and linger much longer.

“Rocket launches are a unique source of pollution, injecting harmful chemicals directly into the upper layers of the atmosphere and contaminating Earth’s last remaining relatively pristine environment,” Barker said. “Though this soot’s impact on climate is currently much smaller than other industrial sources, its potency means we need to act before it causes irreparable harm.”

Space may look empty from the ground. It is not. Each launch leaves a chemical trace. As satellite internet systems spread across low Earth orbit, those traces are starting to add up.