**Scientists have predicted a fall in the number of satellites that can sustainably operate in low-Earth orbit (LEO), because of the impact of climate change on the atmosphere.**
According to a new study from the Massachusetts Institute of Technology (MIT), greenhouse gas emissions are causing the upper atmosphere, known as the thermosphere, to shrink, which changes the way bodies orbit around the Earth.
Satellites in LEO reduce the latency effect associated with those operating in a much higher orbit. This is particularly beneficial to the growing satellite constellations that aim to give total broadband internet coverage around the world, such as services from Starlink and [Amazon’s Project Kuiper](https://eandt.theiet.org/2025/01/06/amazons-satellite-operation-plans-launch-uk-broadband-service). There are already over 10,000 satellites operating in LEO.
When the thermosphere contracts, its decreasing density reduces atmospheric drag – a force that pulls old satellites and other debris down to altitudes where they will encounter air molecules and burn up.
This reduced drag therefore extends the lifetime for space junk, which orbits for longer periods before drag eventually brings it back down to Earth. This has the potential to increase the number of collisions in orbit faced by satellites and places a de facto cap on the number that can safely operate at any given time.
The MIT team carried out simulations of how carbon emissions affect the upper atmosphere and orbital dynamics in order to estimate the ‘satellite-carrying capacity’ of LEO. Their simulations predict that by the year 2100, the carrying capacity of the most popular regions could be reduced by 50-66% because of the effects of greenhouse gases.
“Our behaviour 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.
“The upper atmosphere is in a fragile state as climate change disrupts the status quo,” explained lead author William Parker. “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 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 past 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 added. “And we can see this by how the drag on our satellites is changing.”