Impacts of projected climate change in the thermosphere on the future space debris environment

Over the past 50-60 years, a decline in the density of the thermosphere has been observed of about 2% per decade at 400 km altitude. This is largely attributed to the increase in atmospheric CO₂ concentration, causing cooling and contraction across the stratosphere, mesosphere, and thermosphere. The reduction in thermospheric density reduces drag on active satellites and space debris, affecting orbital characteristics and increasing debris lifetimes. To manage the risk of the growing space debris population and ensure the long-term sustainability of the Low Earth Orbit (LEO) environment, we need to understand the impacts of likely future density changes. Here we used a long transient simulation with the Whole Atmosphere Community Climate Model eXtension (WACCM-X) 2.0 to define future density scenarios used as input for simulations with the Realisations of the Engineered and Natural Evolution of the Global Atmosphere and Debris Environment (RENEGADE) model. The WACCM-X simulation followed Shared Socio-economic Pathway 2–4.5 and included realistic assumptions on main magnetic field changes and variations in solar activity, which also affect the climate of the upper atmosphere. RENEGADE simulations under a "best-case" scenario for debris generation showed that the projected long-term density trend would lead to ∼8% more objects in LEO by 2070 and a significantly enhanced average collision rate, from 0.22±0.01 to 0.25±0.01 per year. The largest enhancements in debris spatial density, of around 30-35% by 2070, were found at ∼400 km altitude. The thermospheric density trend will therefore have a disproportionally large impact on infrastructure operating around this altitude.