Carrying Capacity for Satellites is Being Affected by Climate Change

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Student Summary by Olivia Hwang

Original Source: William E. Parker et al., Science Journal for Kids, July 2025

https://www.sciencejournalforkids.org/wp-content/uploads/2025/07/space-debris_article.pdf; https://www.nature.com/articles/s41893-025-01512-0

Abstract

Background: High numbers of satellites and space stations orbit Earth in the thermosphere and exosphere (the top layers of our atmosphere), which together are called low Earth orbit. Scientists have found that climate change is cooling down the thermosphere, lowering its density and therefore causing it to thin and shrink. (Greenhouse gas molecules absorb and give off heat at all altitudes. Close to Earth, the heat they give off is trapped by other molecules. In the upper atmosphere there are far fewer molecules, so that heat escapes to space instead, which cools the thermosphere.) When the air is less dense, the drag is also weaker. Consequently, satellites would be able to stay in orbit for longer periods of time. It is also important to note that there are high quantities of space debris caused by satellite collisions in low Earth orbit. If there were enough collisions, this could cause a chain reaction called the Kessler syndrome. If the Kessler syndrome were to occur, communication would be limited, transportation using GPS would be impossible, and much more.

Objective: Scientists wanted to know the carrying capacity for satellites in low Earth orbit without causing the Kessler syndrome (a number referenced as the instantaneous Kessler capacity), as well as the effects of climate change on this number over time.

Method: Using models from the National Center for Atmospheric Research and the U.S. Naval Research Laboratory, scientists modeled changes in thermospheric density until the year 2100. They did this for three different climate scenarios — ideal, average, and severe — which came from the Intergovernmental Panel on Climate Change. They then compared the instantaneous Kessler capacity of these scenarios to their calculated instantaneous Kessler capacity for their baseline estimate of greenhouse gas levels from the year 2000.

Results: Scientists found that the Kessler capacity decreased during solar minimums (the period of lowest solar activity in an 11-year cycle) and in more severe climate change scenarios. They also noted that the baseline instantaneous Kessler capacity was 34–72 million satellites. Furthermore, scientists predicted that by 2100 there could be a 50–66% reduction in capacity at altitudes of 200–400 km, and a 60–82% reduction from 400–1,000 km.

Conclusion: Overall, this study is important because it shows that climate change will lower the number of satellites low Earth orbit can safely hold. As the thermosphere thins, drag weakens, so satellites and debris stay in orbit longer and have more chances to collide. This raises the risk of the Kessler syndrome. It raises awareness that we must think about our sustainable use of low Earth orbit before it is too late.