They say that, under the highest-emission scenario, low Earth orbit will be unattainable for up to two-in-three of our current satellites – or around 25 – 40 million satellites – by 2100. This is because Earth’s upper atmosphere will cool and shrink in response to greenhouse gas increases, reducing the volume of space available to host orbiting satellites, they say.

William Parker and colleagues used atmospheric modelling to estimate the number of satellites that can be sustainably maintained in Earth’s orbit by 2100 under different emission scenarios.

Using the greenhouse gas concentration in the year 2000 as a baseline, Parker and colleagues found that the maximum number of satellites that can be sustainably managed in low Earth orbit will be 50–66% less by 2100, dependent on solar activity, under the highest-emission Shared Socio-economic Pathway scenario.

Although active deorbiting technologies are being considered to reduce the risk of collisions, the authors suggest that mitigating greenhouse gas emissions is not only important for Earth’s climate but also for preserving our access to and use of outer space.