The longwave feedback λ characterizes how Earth’s outgoing longwave radiation changes with surface temperature Ts, making it an important quantity to estimate Earth’s climate sensitivity. Compared to the traditionally studied λ, its spectrally resolved counterpart λν offers deeper insights into the underlying physical processes. Both λ and λν are known to vary with Ts, but this Ts dependence has so far only been investigated using models. Here, we derive the clear-sky spectral longwave feedback λν for surface temperatures Ts between 210K and 310K based on observations of the AIRS instrument onboard the Aqua satellite. We disentangle the radiative signatures of the atmospheric general circulation by simulating λν based on a single-column model with different degrees of idealization. We find that at low Ts, the observed λν is dominated by the surface response and sensitive to biases in Earth’s skin temperature. At higher Ts, changes in atmospheric temperature and humidity, as well as their vertical distribution, play an important role in shaping λν . These changes impact both the absorption of surface emission in the atmospheric window and the atmospheric emission in the water vapor and CO2 absorption bands. Our results demonstrate that we can fully understand the observed λν at a wide range of Ts using a simple conceptual model of Earth’s atmosphere. This understanding can be used to better constrain changes in R and T with warming in Earth’s climate using satellite observations, as well as for paleoclimate and exoplanet studies.
