Climate change is shrinking Earth’s atmosphere - and that’s bad for satellites

A team of aerospace engineers has recently discovered that climate change is altering conditions in near-Earth space. Over time, these shifts could limit the number of satellites that can reliably operate in Earth’s orbit. 

Led by MIT, the new study indicates that emissions of carbon dioxide and other greenhouse gases are causing the upper atmosphere to contract, reducing drag on older satellites and debris – and thereby threatening to make space more crowded and prone to collisions.

“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,” said study author Richard Linares, an associate professor in MIT’s Department of Aeronautics and Astronautics (AeroAstro).

Satellites highways are closing

The researchers examined the thermosphere, an important atmospheric layer where the International Space Station and the majority of satellites operate. The thermosphere naturally shrinks and expands over an 11-year solar cycle, influenced by the sun’s output. 

However, the MIT team found that greenhouse gases intensify the layer’s contraction, causing densities to drop at high altitudes. As a result, orbiting objects experience less drag, enabling defunct satellites and debris to remain in orbit longer than they otherwise would.

“The upper atmosphere is in a fragile state as climate change disrupts the status quo,” said lead author William Parker, a graduate student at 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.”

According to the team’s simulations, these effects could reduce the “carrying capacity” of certain altitudes for satellites by 50 to 66 percent by the year 2100, meaning the environment can sustain significantly fewer satellites without triggering a surge in collisions.

The future of outdated satellites

When higher atmospheric layers remain dense enough, objects that reach the end of their operational life slowly lose altitude and burn up upon reentry. This self-cleaning mechanism helps clear old satellites and debris. 

However, if drag decreases due to a contracted thermosphere, outdated spacecraft remain aloft for decades, congesting key orbital paths. Thus, less drag means extended lifetimes for space junk, which will litter various regions for decades, increasing the potential for collisions in orbit.

To arrive at this conclusion, the researchers created models of how carbon emissions affect the thermosphere and influence orbital behavior. 

They then used these models to estimate the “satellite carrying capacity” of low-Earth orbit – a concept borrowed from ecology, referring to the maximum population an ecosystem (or, in this case, a region of space) can support without detrimental outcomes.

How many satellites can safely coexist?

The study involved simulating possible future greenhouse gas emissions in order to see how atmospheric density could evolve. They tested various scenarios of continued emissions growth, as well as one in which the emissions stayed at their level from the year 2000. 

Next, they factored in known orbital dynamics and possible collisions to figure out how many satellites at different altitudes could safely coexist before collisions and debris would spiral out of control.

By 2100, the number of satellites safely accommodated within the altitudes of 200 and 1,000 kilometers might be reduced by 50 to 66% compared with a scenario in which emissions remain at year-2000 levels. 

If space operators exceed this capacity at a given altitude, the experts warn of a “runaway instability,” in which one collision creates enough shards of debris that future collisions become much more likely.

Even in a local region, we seem to be close to approaching this capacity value today since thousands of new satellites now populate low-Earth orbit, especially from so-called megaconstellations like SpaceX’s Starlink, which provides satellite-based internet. 

A shifting debris environment

Nowadays, there are more than 10,000 satellites in low-Earth orbit and we rely on the atmosphere to clean up the debris. But if the atmosphere is changing, the debris environment will also change. 

These satellites deliver vital services . communication, internet, weather data, navigation – but their population growth forces many to perform regular collision-avoidance maneuvers.

If the atmosphere keeps thinning at key orbits, older and no-longer-functional craft won’t reenter and disintegrate as rapidly as they used to. As a result, defunct satellites, boosters, and other pieces of debris could float indefinitely, becoming a hazard to newer missions. 

A single collision in one orbital shell can generate debris that may remain in orbit for decades or centuries, triggering subsequent collisions.

“We show the long-term outlook on orbital debris is critically dependent on curbing our greenhouse gas emissions,” Parker said.

Consequences of global warming

In the midst of rapid satellite deployments, these results underline the need for improved space-traffic management and collision-avoidance protocols to keep orbits safe. 

The simulations also provide compelling motivation for reducing greenhouse gas emissions worldwide. 

“The megaconstellation is a new trend and we’re showing that because of climate change, we’re going to have a reduced capacity in orbit,” Linares explained.

By examining the intersection of climate and orbital dynamics, the researchers have uncovered one more factor that highlights the far-reaching consequences of global warming. 

“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,” Linares concluded.

The study is published in the journal Nature Sustainability.

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