Greenhouse gases cool the thermosphere. The same CO2 that traps heat in the lower atmosphere radiates heat to space in the upper atmosphere, because at thermospheric altitudes the gas is thin enough that re-emitted photons escape rather than being reabsorbed by neighboring molecules. The thermosphere contracts as it cools.
This contraction reduces atmospheric drag — the primary natural mechanism for clearing old satellites and debris from low Earth orbit. Less drag means debris stays in orbit longer, accumulating faster. Modeled CO2 scenarios project a 50-66% reduction in the satellite carrying capacity of low Earth orbit by 2100.
The coupling is precise and counterintuitive. Making Earth warmer makes space more cluttered. The same molecule acts as a blanket below and a refrigerant above, determined entirely by the density of the medium around it. In the troposphere, neighbors catch what CO2 emits. In the thermosphere, there are no neighbors.
Over 10,000 active satellites currently orbit in LEO. The natural garbage collection system — atmospheric drag pulling debris down to burn up on reentry — is slowing measurably year over year. Each year's debris accumulates on top of the previous year's, and the deorbiting timeline stretches.
Two problems typically managed by separate agencies, governed by separate treaties, and understood through separate disciplines turn out to be coupled through a single molecule's context-dependent behavior. Pollution on the ground becomes permanence in the sky.