Energy Conservation in a Cooling and Contracting Thermosphere

Time series of infrared radiated power by thermospheric nitric oxide (NO) and carbon dioxide (CO 2 ), and their total power (NO + CO 2 ) (measured by the SABER instrument on the NASA TIMED satellite from 2002 through 2023) have been analyzed for long‐term trends. Solar and geomagnetic indices (F 10.7 , Ap, Dst) are used with multiple linear regression to provide trend approximations for the radiated infrared power. There are no statistically significant trends observed for NO and total radiated power, and the trend in CO 2 radiated power is not statistically significant at 2‐sigma (95%) confidence level. The thermosphere continues to radiate a constant amount of infrared energy over time after accounting for natural variability, despite more than two decades of cooling due to increasing CO 2 . These results demonstrate energy conservation on decadal timescales and validate the mechanism of thermospheric greenhouse cooling. The long‐term radiometric stability of the SABER instrument enables these results.