Emmert suggests carbon dioxide (CO2) in the thermosphere might play a role in explaining the atmospheric collapse.
This gas acts as a coolant, shedding heat via infrared radiation. It is widely-known that CO2 levels have been increasing in Earth's atmosphere. Extra CO2 in the thermosphere could have magnified the cooling action of solar minimum."
I'm not saying "Oh, what do those darned scientists know?", it's just interesting.