‘Megaconstellation’ satellite systems, such as SpaceX’s Starlink and China’s Qianfan project, will be responsible for nearly half of all air pollution from the space sector by 2030, University College London (UCL) researchers have said.

As of early May 2026, there are over 10,000 active Starlink satellites in low-Earth orbit, easily the largest system of its type so far. While China’s Qianfan has only launched 504 so far, and Amazon’s Project Kuiper only 300, they are aiming for around 15,000 and 3,236 orbiting satellites respectively to complete the constellations.

But a combination of rocket launches, and pollution caused by dead satellites falling back to Earth, is quickly racking up to be the space sectors’ largest individual source of air pollution.

The UCL team said the black carbon, or soot, that is 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.

They used data from rocket launches and satellite deployments between 2020 and 2022 to project the 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, which 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 the 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.

Professor Eloise Marais, lead researcher on the project, 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 surpassed their projections and many more are expected to be launched in the coming years.

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.”