Space lidar observations constrain longwave cloud feedback

Thibault Vaillant de Guélis (1, 2) , Hélène Chepfer (3) , Rodrigo Guzman (2) , Marine Bonazzola (2) , David M. Winker (4) , Vincent Noel (5)

1 LaMP - Laboratoire de Météorologie Physique
2 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
3 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
4 LaRC - NASA Langley Research Center [Hampton]
5 LAERO - Laboratoire d'aérologie

Some of the most challenging questions in atmospheric science relate to how clouds will respond as the climate warms. On centennial scales, the response of clouds could either weaken or enhance the warming due to greenhouse gas emissions. Here we use space lidar observations to quantify changes in cloud altitude, cover, and opacity over the oceans between 2008 and 2014, together with a climate model with a lidar simulator to also simulate these changes in the present-day climate and in a future, warmer climate. We find that the longwave cloud altitude feedback, found to be robustly positive in simulations since the early climate models and backed up by physical explanations, is not the dominant longwave feedback term in the observations, although it is in the model we have used. These results suggest that the enhanced longwave warming due to clouds might be overestimated in climate models. These results highlight the importance of developing a long-term active sensor satellite record to reduce uncertainties in cloud feedbacks and prediction of future climate.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]

Thibault Vaillant de Guélis, Hélène Chepfer, Rodrigo Guzman, Marine Bonazzola, David M. Winker, et al.. Space lidar observations constrain longwave cloud feedback. Scientific Reports, 2018, 8 (1), ⟨10.1038/s41598-018-34943-1⟩. ⟨hal-01916591⟩