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Speaker: Florian Roemer, Universität Hamburg, Germany

Title: "Using satellite observations to spectrally resolve Earth’s radiative response to warming"

Abstract: The spectral longwave feedback parameter λ_ν represents how Earth’s outgoing longwave radiation adjusts to temperature changes and is thus the detailed fingerprint of all fast longwave feedbacks, directly impacting Earth’s climate sensitivity. Most research so far has focused on the spectral integral of λ_ν. Spectrally resolving λ_ν permits inferring information about the vertical distribution of longwave feedbacks, thus gaining a better understanding of the underlying processes. However, investigations of λ_ν have so far been largely limited to model studies. We infer the global all-sky λ_ν using satellite observations of seasonal and interannual variability taken by the Infrared Atmospheric Sounding Interferometer (IASI). We find that spectral bands subject to strong water vapour absorption exhibit a substantial stabilising net feedback. We demonstrate that this stabilising feedback is caused by a decrease in relative humidity with warming, the radiative fingerprints of which can be directly observed. Therefore, our findings emphasise the importance of better understanding processes affecting the present distribution and the future trends of relative humidity. This first observational constraint on the global all-sky λ_ν can be used as a powerful tool to evaluate the representation of longwave feedbacks in global climate models and to better constrain Earth’s climate sensitivity.

Bio: Florian Roemer is a PhD student in Meteorology at the Universität Hamburg and the International Max Planck Research School on Earth System Modelling, working with Stefan Buehler. His research lies at the intersection between radiative transfer and climate science, with a particular focus on radiative feedbacks. He obtained his B.Sc. and M.Sc. in Meteorology at the Universität Hamburg.