CO2 Turns the Stratosphere Into a Cooling Engine, New Study Finds

New Columbia University–led research, published in Nature Geoscience, identifies why Earth’s upper atmosphere has cooled while the surface warms: increasing CO2 alters how infrared light is absorbed and emitted in the stratosphere, with a particular “Goldilocks zone” of wavelengths driving efficient cooling that expands as CO2 rises. Ozone and water vapor play smaller roles. Cooling strengthens with altitude, and about a doubling of CO2 cools the stratopause by ~8°C, contributing to less heat escaping to space and a feedback that traps more heat near the surface. The study provides a quantitative mechanism for stratospheric cooling and has implications for understanding atmospheres beyond Earth.