Greenhouse gases are doing more than warming our planet — they’re reshaping space itself. As emissions cool and shrink the thermosphere, satellites experience less drag, allowing more space junk to linger in orbit.
With thousands of new satellites launching every year, this congestion could lead to an orbital traffic jam, raising the risk of catastrophic collisions. If emissions continue unchecked, experts predict that by 2100, space could be so crowded that it becomes unsustainable for future missions.
Shrinking Space: Greenhouse Gases Threaten Satellite Sustainability
MIT aerospace engineers have discovered that greenhouse gas emissions are altering near-Earth space in a way that could significantly reduce the number of satellites that can operate there sustainably over time.
Their study, published in Nature Sustainability, reveals that carbon dioxide and other greenhouse gases are causing the upper atmosphere to shrink. This effect is particularly concerning in the thermosphere — the region where most satellites, including the International Space Station, orbit. As the thermosphere contracts, air density decreases, which in turn reduces atmospheric drag. Normally, this drag helps clear space debris by pulling old satellites and junk into lower altitudes, where they burn up upon reentry.
Space Junk Crisis: Why Less Drag Spells Trouble
With less drag, space debris lingers longer in orbit, increasing congestion and the risk of collisions.
To understand the long-term impact, the MIT team ran simulations on how carbon emissions influence the upper atmosphere and orbital dynamics. Their models predict that by 2100, the “satellite carrying capacity” — the number of satellites that can safely operate in low-Earth orbit—could shrink by 50 to 66 percent due to these atmospheric changes.
Climate Change and Space Operations: A Delicate Balance
“Our behavior with greenhouse gases here on Earth over the past 100 years is having an effect on how we operate satellites over the next 100 years,” says study author Richard Linares, associate professor in MIT’s Department of Aeronautics and Astronautics (AeroAstro).
“The upper atmosphere is in a fragile state as climate change disrupts the status quo,” adds lead author William Parker, a graduate student in AeroAstro. “At the same time, there’s been a massive increase in the number of satellites launched, especially for delivering broadband internet from space. If we don’t manage this activity carefully and work to reduce our emissions, space could become too crowded, leading to more collisions and debris.”
The study includes co-author Matthew Brown of the University of Birmingham.
Sky Fall: The Thermosphere’s Natural Cycle vs. Human Impact
The thermosphere naturally contracts and expands every 11 years in response to the sun’s regular activity cycle. When the sun’s activity is low, the Earth receives less radiation, and its outermost atmosphere temporarily cools and contracts before expanding again during solar maximum.
In the 1990s, scientists wondered what response the thermosphere might have to greenhouse gases. Their preliminary modeling showed that, while the gases trap heat in the lower atmosphere, where we experience global warming and weather, the same gases radiate heat at much higher altitudes, effectively cooling the thermosphere. With this cooling, the researchers predicted that the thermosphere should shrink, reducing atmospheric density at high altitudes.
Tracking Atmospheric Changes: Satellites Reveal the Shift
In the last decade, scientists have been able to measure changes in drag on satellites, which has provided some evidence that the thermosphere is contracting in response to something more than the sun’s natural, 11-year cycle.
“The sky is quite literally falling — just at a rate that’s on the scale of decades,” Parker says. “And we can see this by how the drag on our satellites is changing.”
The MIT team wondered how that response will affect the number of satellites that can safely operate in Earth’s orbit. Today, there are over 10,000 satellites drifting through low-Earth orbit, which describes the region of space up to1,200 miles, or 2,000 kilometers, from Earth’s surface. These satellites deliver essential services, including internet, communications, navigation, weather forecasting, and banking. The satellite population has ballooned in recent years, requiring operators to perform regular collision-avoidance maneuvers to keep safe. Any collisions that do occur can generate debris that remains in orbit for decades or centuries, increasing the chance for follow-on collisions with satellites, both old and new.
“More satellites have been launched in the last five years than in the preceding 60 years combined,” Parker says. “One of key things we’re trying to understand is whether the path we’re on today is sustainable.”
Crowded Shells: Simulating the Future of Orbital Traffic
In their new study, the researchers simulated different greenhouse gas emissions scenarios over the next century to investigate impacts on atmospheric density and drag. For each “shell,” or altitude range of interest, they then modeled the orbital dynamics and the risk of satellite collisions based on the number of objects within the shell. They used this approach to identify each shell’s “carrying capacity” — a term that is typically used in studies of ecology to describe the number of individuals that an ecosystem can support.
“We’re taking that carrying capacity idea and translating it to this space sustainability problem, to understand how many satellites low-Earth orbit can sustain,” Parker explains.
The team compared several scenarios: one in which greenhouse gas concentrations remain at their level from the year 2000 and others where emissions change according to the Intergovernmental Panel on Climate Change (IPCC) Shared Socioeconomic Pathways (SSPs). They found that scenarios with continuing increases in emissions would lead to a significantly reduced carrying capacity throughout low-Earth orbit.
Runaway Instability: The Cascade of Collisions Ahead
In particular, the team estimates that by the end of this century, the number of satellites safely accommodated within the altitudes of 200 and 1,000 kilometers could be reduced by 50 to 66 percent compared with a scenario in which emissions remain at year-2000 levels. If satellite capacity is exceeded, even in a local region, the researchers predict that the region will experience a “runaway instability,” or a cascade of collisions that would create so much debris that satellites could no longer safely operate there.
Their predictions forecast out to the year 2100, but the team says that certain shells in the atmosphere today are already crowding up with satellites, particularly from recent “megaconstellations” such as SpaceX’s Starlink, which comprises fleets of thousands of small internet satellites.
“The megaconstellation is a new trend, and we’re showing, because of climate change, we’re going to have a reduced capacity in orbit,” Linares says. “And in local regions, we’re close to approaching this capacity value today.”
The Atmosphere’s Role in Space Debris Cleanup
“We rely on the atmosphere to clean up our debris. And if the atmosphere is changing, then the debris environment will change too,” Parker adds. “We show the long-term outlook on orbital debris is critically dependent on curbing our greenhouse gas emissions.”
Explore Further: The Surprising Link Between CO2 Levels and Satellite Collisions
Reference: “Greenhouse gases reduce the satellite carrying capacity of low Earth orbit” by William E. Parker, Matthew K. Brown and Richard Linares, 10 March 2025, Nature Sustainability.
DOI: 10.1038/s41893-025-01512-0
This research is supported in part by the U.S. National Science Foundation, the U.S. Air Force, and the U.K. Natural Environment Research Council.
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1 Comment
Nice way to deflect the blame from the idiots who put that junk up there in the first place.