The rapid expansion of satellite megaconstellations, led by companies like SpaceX, is driving a surge in rocket launches that may be altering Earth’s atmosphere in unintended ways. A May 2024 study published in Earth’s Future found that black carbon emissions from kerosene-fueled rockets are accumulating 10 to 12 kilometers above the surface, where they reflect sunlight and cool the lower atmosphere—a phenomenon similar to stratospheric aerosol injection, a controversial geoengineering proposal. While current levels are small compared to global warming from greenhouse gases, the effect per unit of soot is about 500 times stronger than ground-based emissions.

Researchers led by Eloise Marais at University College London project that pollution from satellite deployments will account for 42% of the space sector’s total climate impact by 2029, up from 35% in 2020. The growth in launches—296 in 2025 alone, deploying over 4,400 satellites—has outpaced earlier projections, suggesting the actual impact could be even higher. Most current rockets don’t emit strong ozone-depleting chemicals, but future propellants may include chlorine-based fuels, raising additional concerns.

Scientists stress that this trend amounts to an untested, unregulated experiment in atmospheric modification. They are developing tools to track emissions and call for policy action to prevent long-term environmental harm. Without better monitoring and regulation, the benefits of global satellite coverage could come with hidden climate costs.