Speaker
Description
The longwave feedback λ characterizes how Earth’s outgoing longwave radiation changes with surface temperature Ts, directly impacting climate sensitivity. Compared to λ, its spectrally resolved counterpart λν offers deeper insights into the underlying physical processes. Both λ and λν vary with Ts, but this Ts dependence has so far only been investigated using models. Here, we derive the clear-sky λν for Ts between 210K and 310K based on observations of the AIRS instrument. 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 the vertical distributions of atmospheric temperature and relative humidity 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 model of Earth’s atmosphere, lending further support to estimates of the clear-sky longwave λ, Earth’s most fundamental climate feedback. They also highlight the effect of different assumptions about Earth’s atmosphere on λ. Similar approaches can be used to better constrain changes in relative humidity and temperature with warming using satellite observations, as well as for paleoclimate and exoplanet studies.
