Earth’s changing climate does not only have an effect on the planet’s oceans, wildlife, and agriculture, it may also impact its surrounding space. New research examines the effect of greenhouse gases on Earth’s upper atmosphere, suggesting that it will shrink over time and become less capable of holding as many satellites as it does now.
Using simulations of carbon emissions over time, a team of scientists from MIT is predicting a shocking drop in the satellite-carrying capacity of low Earth orbit. They concluded that, as the uppermost atmosphere shrinks, debris will linger longer, and the resulting reduction in atmospheric drag could increase the risk of collisions in space. The team predicts that by the year 2100, the carrying capacity of the most popular regions could be reduced by 50 to 66% due to the effects of greenhouse gases, according to a study published Monday in Nature Sustainability.
“As greenhouse gas concentrations rise, they warm the troposphere where we live but cool and contract the upper atmosphere—the stratosphere, mesosphere, and thermosphere,” William Parker, a graduate student at the department of aeronautics and astronautics at MIT, told Gizmodo. “The thermosphere plays a crucial role in creating drag on orbital debris, gradually removing it from space. However, as the atmosphere contracts due to increasing greenhouse gas emissions, debris remains in orbit longer, increasing the risk of a runaway cascading collision scenario.”
The thermosphere is where the International Space Station and most other satellites orbit Earth. More than 10,000 satellites are currently drifting through low Earth orbit. With rising emissions, the chances of collision between spacecraft increase, which will lead to the creation of more space debris. That will reduce the number of satellites that are able to operate in low Earth orbit within the same risk threshold that’s applied today.
Greenhouse gases act like a blanket, warming the troposphere by insulating the surface and reflecting heat back toward the ground, Parker explained. The retention of heat in the troposphere means less heat makes its way into the upper atmosphere. Additionally, the heat that does make its way to the upper atmosphere is radiated out into space by greenhouse gases.
“These two contributions lead to long-term cooling in the stratosphere, mesosphere, and thermosphere. That cooling leads to contraction,” Parker added. “If you’ve ever put a balloon in a freezer, you’ll know that as the temperature drops, the balloon shrinks.” The same thing is happening to the upper atmosphere on a global scale.
The researchers behind the study simulated different scenarios over the coming century, one in which greenhouse gas concentrations remain at the same level from the year 2000 and others where emissions change according to the Intergovernmental Panel on Climate Change (IPCC) Shared Socioeconomic Pathways (SSPs). The increase of emissions over time led to a significantly reduced carrying capacity through low Earth orbit.
“Without an atmosphere, most space debris would remain in orbit indefinitely,” Parker said. “As the atmosphere thins, debris lingers longer, increasing the risk to active satellites. With the growing consequences of space debris, we can accommodate fewer debris-generating events.”
With the estimated reduction of the number of satellites in low Earth orbit over time, the study warns that if satellite capacity is exceeded in a particular region, it may lead to a “runaway instability,” or a cascade of collisions that would create so much debris that satellites would no longer be able to safely operate there.
As the space industry continues to grow at unprecedented rates, so does the demand for spacecraft in Earth orbit. In 2023, there was a 35% increase in the total number of active satellites orbiting Earth. That number will likely increase over time.
The researchers behind the study suggest that proactive measures need to be taken today, as well as better decisions over the number of satellites being launched to space. “More satellites have been launched in the last five years than in the preceding 60 years combined,” Parker said. “One of [the] key things we’re trying to understand is whether the path we’re on today is sustainable.”
