Observational evidence for a negative shortwave cloud feedback in middle to high latitudes

• Published in: Geophysical research letters Vol. 43; no. 3; pp. 1331 - 1339
• Main Authors: Ceppi, Paulo, McCoy, Daniel T., Hartmann, Dennis L.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.02.2016
• Subjects: climate; climate change; climate feedbacks; Climate models; Cloud amount; Clouds; Feedback; Geophysics; Histograms; Historic; Historic temperatures; Historical structures; History; Latitude; Mathematical models; Meteorology; Negative feedback; Observational studies; Optical analysis; Optical thickness; Temperature; Thickening
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL067499

Exploiting the observed robust relationships between temperature and optical depth in extratropical clouds, we calculate the shortwave cloud feedback from historical data, by regressing observed and modeled cloud property histograms onto local temperature in middle to high southern latitudes. In this region, all CMIP5 models and observational data sets predict a negative cloud feedback, mainly driven by optical thickening. Between 45° and 60°S, the mean observed shortwave feedback (−0.91 ± 0.82 W m−2 K−1, relative to local rather than global mean warming) is very close to the multimodel mean feedback in RCP8.5 (−0.98 W m−2 K−1), despite differences in the meridional structure. In models, historical temperature‐cloud property relationships reliably predict the forced RCP8.5 response. Because simple theory predicts this optical thickening with warming, and cloud amount changes are relatively small, we conclude that the shortwave cloud feedback is very likely negative in the real world at middle to high latitudes. Key Points A negative shortwave cloud feedback is observed in middle to high southern latitudes This negative feedback results from increasing cloud optical depth with temperature Models are in qualitative agreement with observations in middle to high latitudes