Direct observation of Earth’s spectral long-wave feedback parameter

• Published in: Nature geoscience Vol. 16; no. 5; pp. 416 - 421
• Main Authors: Roemer, Florian E., Buehler, Stefan A., Brath, Manfred, Kluft, Lukas, John, Viju O.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2023; Nature Publishing Group
• Subjects: 704/106/35/823; 704/106/694; 704/106/694/2786; Climate; Climate feedback; Climate models; Climate sensitivity; Distribution; Earth; Earth and Environmental Science; Earth Sciences; Earth System Sciences; Feedback; Geochemistry; Geology; Geophysics/Geodesy; Global climate; Global climate models; Humidity; Interannual variability; Long wave radiation; Outgoing long-wave radiation; Parameter sensitivity; Relative humidity; Satellite observation; Satellites; Seasonal variability; Spectral bands; Spectral sensitivity; Stabilizing; Temperature changes; Vertical distribution; Water vapor
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/s41561-023-01175-6

The spectral long-wave feedback parameter represents how Earth’s outgoing long-wave radiation adjusts to temperature changes and directly impacts Earth’s climate sensitivity. Most research so far has focused on the spectral integral of the feedback parameter. Spectrally resolving the feedback parameter permits inferring information about the vertical distribution of long-wave feedbacks, thus gaining a better understanding of the underlying processes. However, investigations of the spectral long-wave feedback parameter have so far been limited mostly to model studies. Here we show that it is possible to directly observe the global mean all-sky spectral long-wave feedback parameter using satellite observations of seasonal and interannual variability. We find that spectral bands subject to strong water-vapour absorption exhibit a substantial stabilizing net feedback. We demonstrate that part of this stabilizing feedback is caused by the change of relative humidity with warming, the radiative fingerprints of which can be directly observed. Therefore, our findings emphasize the importance of better understanding processes affecting the present distribution and future trends in relative humidity. This observational constraint on the spectral long-wave feedback parameter can be used to evaluate the representation of long-wave feedbacks in global climate models and to better constrain Earth’s climate sensitivity. Earth’s spectral long-wave feedback parameter can be directly observed using satellite measurements, revealing the influence of relative humidity on climate feedbacks.