Whether your views on climate change are informed by politics or science, it’s getting harder to ignore it’s effects on our lives down here on Earth. But a surprising study reports that increasing concentrations of greenhouse gases in our atmosphere could also be affecting the problem of space junk. As the heat energy stored in our atmosphere increases, its ability to scrub debris from Low-Earth Orbit (LEO) decreases, increasing the risk of satellite collisions and making it more likely that humanity could lose access to space entirely.
Most predictions about climate change focus on things that affect our daily lives. Extreme weather, rising sea levels, impacts on agriculture, and populated areas becoming uninhabitable. That’s because when we think of our atmosphere, we mostly only consider the lowest, thickest layer called the troposphere. But in Greenhouse gases reduce the satellite carrying capacity of low Earth orbit, a paper published in Nature sustainability, William E. Parker and Richard Linares of the Massachusetts Institute of Technology, and Matthew Brown of the University of Birmingham argue that the effects of climate change extend outwards into space as well.
The atmosphere
The lowest layer of the atmosphere is called the troposphere, and it has most of the air, by mass. It marks the space where air is thick enough to support life. It’s a turbulent region which extends to altitudes from about 5 km at the poles to 18 km at the equator. When weather reports talk about cold fronts and high pressure regions, rainfall and temperature, all of that happens within the troposphere.
But there are extra layers higher up. After the troposphere comes the stratosphere, extending up to about 50 km. Above that, a climbing rocket reaches the mesosphere, and then the thermosphere. The thermosphere begins just a little beneath the Kármán line and stretches up to almost 700km. It is named for it’s very high temperature (up to 2500°C, although an astronaut wouldn’t actually feel that heat – the air molecules are so thinly spread out that they can’t conduct their heat to solid objects). This is the same range of altitudes occupied spacecraft and satellites in LEO.
The air in the thermosphere is close enough to a vacuum that spacecraft can travel through them at orbital velocities, but not so thin that there isn’t still a tiny bit of drag. This means that satellites in LEO are constantly slowing down, and gradually losing altitude. If they are not periodically given a boost, they will inevitably re-enter and burn up in the troposphere.
Kessler syndrome
Scientist and space industry experts have been raising the alarm for decades now about the risk of space junk. As much as astronomers love describing the sheer vastness of space, the LEO region where most artificial satellites live is actually quite small. It’s a thin shell, only a few hundred kilometers above our heads, and the various objects orbiting there are moving many tens of times faster than a sniper’s rifle bullet.
Collisions can and do happen, and the results can be spectacular. Even tiny specks of paint, when impacting the satellites and spacecraft at those speeds, leave small craters in their structure. If enough debris accumulates, these collisions will become more frequent, which would in turn generate even more debris faster and faster, causing more collisions, resulting in a chain reaction that we call Kessler syndrome, which would eventually destroy all artificial satellites and make it impossible for any spacecraft to survive travel through space near Earth. If this happens, we would lose all access to space; not just for astronauts exploring the solar system, but space telescopes, communication relays, and earth observation platforms used by firefighters, the military, conservationists and climate scientists.
Kessler syndrome is not inevitable, however. Space debris does not stay in space forever. The thin air of the thermosphere creates a tiny amount of drag on all objects in LEO, so every piece of junk will eventually re-enter the Earth’s atmosphere and burn up. LEO is a self-cleaning region of space. That means that the real question to worry about is “How many collisions with meteoroids and existing human-made debris can happen before we’re adding debris faster than it can fall out of the sky?”
Unfortunately, when it comes to Kessler syndrome, the Greenhouse gases paper is bad news. It reminds us that the climate change is being caused by a general warming of the planet, caused by greenhouse gases blocking heat energy that would otherwise have radiated out into space. But it then adds that this energy is trapped in the lower layers of the atmosphere. That means that, while the troposphere and oceans grow warmer and more energetic, the outer layers of the thermosphere and exosphere actually become colder. When a gas cools down, it becomes more dense and tries to sink to a lower altitude. This makes the thermosphere thinner, reducing drag on objects orbiting at low altitudes, and meaning that space debris will hang around for much longer, which in turn means that Kessler syndrome becomes more likely to happen.
Protecting space
At the moment, the space industry is being dominated by tech companies who are advancing the state of rocketry to make space travel much more affordable, and who are using their own technology to launch mega-constellations of communications satellites. These companies are currently in the cross-hairs of environmental activists. This is not only because their satellite mega-constellations are making it increasingly difficult for both professional and amateur astronomers to observe the universe, but also because of their plans to build vast data-centers to power the AI revolution. These data-centers need enormous amounts of power to run, and are believed to be one reason why many tech companies are quietly walking back on prior carbon-reduction commitments.
It’s ironic that the same companies working so hard to open up space for commercial and industrial use are also contributing to killing that same dream. But we can hope that these companies will realize that they can’t build a business that relies on record-breaking numbers of satellites in LEO if those satellites are continuously smashing each other to pieces. If they are to keep making a profit from space, they will first be forced to protect our environment.