Satellite launch pollution rapidly accumulating in the upper atmosphere

The potent pollution from so-called “megaconstellation” satellite systems launched en masse into space since 2019 will account for nearly half (42%) of the total climate impact of space sector pollution by the end of the decade, finds a new study led by UCL researchers.

Publishing in Earth’s Future, the research team examined air pollution produced by the growing number of rocket launches, and the discarded rocket bodies and dead satellites falling back to Earth. The black carbon (soot) generated from these sources lingers in the upper atmosphere far longer than that from ground-based sources, resulting in a 500-fold greater impact on the climate.

Using data from rocket launches and satellite deployments between 2020 and 2022, the team projected emissions out to the end of the decade. The analysis showed that in 2020 these megaconstellations contributed about 35% to the total climate impact from the space sector and will climb to 42% by 2029.

The research also found that the potent air pollution generated by the launch and re-entry of large, disposable satellite systems is rapidly accumulating in the upper atmosphere, decreasing the amount of sunlight reaching Earth’s surface. By 2029, the accumulating pollution would have an effect similar to proposed geoengineering techniques, which aim to cool the planet by blocking some sunlight with particles injected into the upper atmosphere.

The research indicated that not all the environmental impacts of the satellites will be negative. Soot from rocket launches has a mild cooling effect on Earth’s climate. However, this effect will be minimal compared with how much the planet’s temperature is set to rise over the same period due to global warming.

Project lead, Professor Eloise Marais (UCL Geography) said: “The space industry pollution is like a small-scale, unregulated geoengineering experiment that could have many unintended and serious environmental consequences. 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. So far there has been limited effort to effectively regulate this type of pollution.”

Additionally, the researchers say that their predictions are likely to be an underestimate. They based their future projections on trends over the first few years (2020 to 2022) of the satellite “megaconstellation” era, but the number of rocket launches between 2023 and 2025 has surpassed their projections and many more are expected to be launched in the coming years.

Professor Marais added: “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, but we need to be extremely cautious.”

Driven by megaconstellations

The research team modelled all the major pollutants from launches and re-entries of satellite megaconstellations, a new class of satellite missions made up of hundreds or thousands of satellites in low Earth orbit that have caused an exponential growth in launches and re-entries in the past few years.

SpaceX’s internet-providing Starlink system is the best known megaconstellation. With nearly 12,000 satellites in orbit so far, it is by far the largest, though rival systems have also deployed hundreds of additional satellites. The authors note that previous estimates projecting another 65,000 satellites launched by the end of the decade are already outdated and likely too conservative in light of recent filings.

The researchers found that though the era of megaconstellations only began in earnest in 2020, these missions now consume more than half of all rocket fuel and are expected to continue to grow. The industry’s zeal to deploy new and expand existing constellations has led to a near tripling of annual rocket launches from 114 in 2020 to 329 in 2025, driven predominantly by SpaceX’s Falcon 9 rockets.

Impact on the atmosphere

The Falcon 9 uses a kerosene-based rocket fuel, which releases soot particles into the upper layers of the atmosphere during launch. Because of slow atmospheric circulation patterns, soot from these launches lingers in the upper layers of the atmosphere for years. This is far longer than soot from Earth-bound sources like cars and power plants which are removed by weather systems like rainfall that effectively wash these pollutants out of the atmosphere. The longer a pollutant persists in the atmosphere, the bigger the impact.

As a result, soot released from these launches are about 540 times more effective at altering climate than soot emitted near Earth’s surface.

The team estimated that by 2029, the space industry will release about 870 tonnes of soot into the atmosphere annually. By comparison, this is akin to what is emitted by all the passenger cars in the UK, totalling 728 tonnes according to the latest emissions values reported by the UK government.

Lead author Dr Connor Barker (UCL Geography) said: “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. 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.”

Ozone depletion

The team also looked at the impact that megaconstellations are having on the overlying ozone layer that protects humanity from harmful ultraviolet radiation from the Sun. Satellite launches can also release chemicals such as chlorine into the atmosphere that can degrade ozone by reacting directly with it. Both launches and re-entries also produce tiny particles that provide reaction surfaces that also speed up ozone depletion reactions.

They found that based on current trends, the impact on the ozone layer from megaconstellation launches will be small, as kerosene-fuelled rockets do not produce chlorine and very few megaconstellations have so far been launched with rockets that emit chlorine. By 2029, collectively all rocket launches will only deplete global ozone by 0.02% compared to 2% due to the ozone-depleting substances that are regulated by the Montreal Protocol. Megaconstellation missions account for less than a tenth of the ozone loss from all 2029 missions.

The deployment of more megaconstellations is already underway, some using fuels that emit chlorine. Amazon is developing its own internet satellite constellation known as Leo, and China is likewise developing its Guowang constellation. Together, these could place tens of thousands of new satellites in orbit, likely requiring dozens or hundreds of launches.

The potential impact of these is uncertain. Amazon-Leo satellites will be launched into orbit using Blue Origin rockets propelled with liquid hydrogen or liquid methane fuel. Neither release chlorine, but some Amazon-Leo contracts are with launch providers that use chlorine-containing solid rockets. Which rockets China plans to use is not clear, but they have so far relied on chlorine-containing solid rockets.

Connor Barker, Eloise Marais, et al, ‘Radiative Forcing and Ozone Depletion of a Decade of Satellite Megaconstellation Missions’ will be published in Earth’s Future on Thursday 14 May 2026, 14:00 UK time, 09:00 US Eastern Time, and is under a strict embargo until this time.

The DOI for this paper will be: https://doi.org/10.1029/2025EF007229

The URL for this paper will be: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/10.1029/2025EF007229