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A study by University College London published in the journal Earth’s Future reveals that the pollution produced by rocket launches and satellite reentry is rapidly accumulating in the upper atmosphere. The soot released in these operations is 540 times more effective in altering the climate than that emitted near the Earth’s surface, and megaconstellations like Starlink are expected to account for 42% of the total climate impact of the space sector by 2029.
The pollution generated by the space industry is no longer a distant problem and has become a topic for researchers studying Earth’s climate. A study led by Professor Eloise Marais from University College London, published in the scientific journal Earth’s Future, shows that the soot or black carbon released by rockets placing satellites in orbit remains in the upper atmosphere for periods between 2.5 and 3 years. The residence time is drastically longer than that of soot emitted by cars and power plants near the surface, which is removed by rain in days or weeks. This accumulation turns space pollution into a climate problem with a disproportionate impact compared to the volume emitted.
The first author of the study, Dr. Connor Barker, from the Department of Geography at UCL, calculated that the soot from rocket launches is 540 times more effective in altering the climate than the soot emitted at the Earth’s surface. The data is alarming because the number of launches almost tripled in five years from 114 in 2020 to 329 in 2025, driven mainly by satellite mega constellations providing high-speed internet, such as SpaceX’s Starlink and Amazon’s Leo constellation.
Why space pollution is so different from terrestrial
The difference between pollution emitted at the surface and that produced by rockets is not just in the quantity, but in the location. When a SpaceX Falcon 9 burns kerosene to carry a load of Starlink satellites into space, soot particles are deposited directly in the upper layers of the atmosphere, above the troposphere, where rain could wash them away. At this altitude, atmospheric circulation is extremely slow, and the pollution remains suspended for years.
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The UCL study estimates that by 2029, the space industry will release about 870 tons of soot per year in these elevated layers. Although the volume seems small compared to the millions of tons emitted by terrestrial sources, the impact is multiplied by the time of permanence. The longer a pollutant stays in the atmosphere, the greater the damage it causes — and space pollution stays there long enough to alter the amount of sunlight reaching the surface.
Mega constellations are the main contributors to the increase
The study analyzed data from satellite launches and deployments between 2020 and 2022, projecting emissions until the end of the decade. The results show that in 2020, mega constellations already contributed 35% of the total climate impact of the space sector, and this share will reach 42% by 2029. Mega constellations currently consume more than half of all the fuel burned by rockets.
SpaceX’s Starlink is the largest and most well-known, with almost 12,000 satellites in orbit. But competing systems, like Amazon’s Leo constellation, have also launched hundreds of satellites. The pollution doesn’t just come from launches: the re-entry of inactive satellites and discarded rocket stages also releases aluminum oxides and other pollutants in the upper layers of the atmosphere, exacerbating the problem.
An unregulated geoengineering experiment
Professor Marais used a comparison that caught the scientific community’s attention: she classified the pollution of the space industry as “a small-scale and unregulated geoengineering experiment, which could have numerous serious and unforeseen environmental consequences.” The reference is not casual. Geoengineering techniques deliberately propose injecting particles into the upper atmosphere to block sunlight and cool the planet, and space pollution is producing a similar effect accidentally.
The study projects that by 2029, the reduction of sunlight caused by launch pollution will be comparable to the effect of some of these geoengineering techniques. The difference is that geoengineering would be planned, monitored, and potentially reversible. Space pollution, on the other hand, is happening without control, without regulation, and without anyone having authorized the experiment. Researchers warn that there is still time to act, as the current impact is small — but the window is closing quickly.
The cooling paradox that is not good news
One of the most counterintuitive findings of the study is that rocket soot produces a slight cooling effect on the climate by blocking some solar radiation. This might sound like positive news in a world facing global warming, but researchers urge caution. The cooling effect is minimal compared to the warming predicted for the same period, and the pollution that causes it brings with it a host of other risks not yet fully understood.
Professor Marais explained that altering the amount of sunlight reaching the surface can have cascading consequences: changes in precipitation patterns, impacts on agriculture, and alterations in sensitive ecosystems. Treating space pollution as an accidental form of geoengineering is not an exaggeration — it is a warning that unknown side effects may arise before any regulation is in place.
The projections that are already outdated
The researchers acknowledge that their estimates are probably below reality. The projections were based on data from 2020 to 2022, the early years of the mega constellation era. Since then, the number of launches between 2023 and 2025 has already exceeded the study’s predictions, and the industry’s expectation is to launch tens of thousands of additional satellites by the end of the decade. Previous projections, which estimated 65,000 new satellites, are already considered outdated.
The pace of growth is driven by competition between SpaceX, Amazon, and other operators for global internet coverage. Starlink alone accounts for nearly 12,000 of the satellites currently in orbit. Each round of new satellites requires more launches, more fuel burned, and more pollution deposited exactly where it causes the most harm. Barker summed up the urgency in one sentence: although the current impact of soot is smaller than that of other industrial sources, its potency means action is needed before the damage becomes irreparable. Space pollution is growing faster than the ability to regulate it, and that is the part that most concerns scientists.
Did you know that rocket soot stays in the atmosphere for years and has a climate impact 540 times greater than surface pollution? What worries you the most: the lack of regulation, the pace of launches, or the effect of accidental geoengineering? Tell us in the comments.
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