Increasing greenhouse gas emissions may threaten satellites  

Increasing levels of human-caused greenhouse gas emissions in the atmosphere may reduce the total number of satellites that can safely orbit Earth by up to 66% of the current carrying capacity by the end of the century, under a high-emissions scenario. The findings from the modelling study are described in Nature Sustainability. 

Previous research has established that an increasing amount of greenhouse gases in the atmosphere can shrink Earth’s upper atmosphere — consisting of the mesosphere (50-85 km) and thermosphere (85-600 km) — as incoming infrared radiation is reflected into space, resulting in a cooling and contracting effect. This contraction reduces the density of Earth’s orbital space, lengthening the amount of time space debris remains in orbit as drag with the atmosphere is reduced. As the number of satellites in Earth’s orbit increases, persistent space debris poses a growing problem for the long-term use of Earth’s orbital space. 

Dr. William Parker from MIT Cambridge 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, the authors 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 (SSP5-8.5) scenario. This is equivalent to approximately 25-40 million satellites. They also estimated the ideal distribution of orbital objects and deviations from this ideal distribution observed under different emission scenarios. The authors show a large decrease in the rate of satellites deorbiting through friction with the atmosphere under the moderate to highest scenario carbon dioxide emission rates. 

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.