Clouds damp the impacts of Polar sea ice loss

• Main Authors: Alkama, Ramdane, Cescatti, Alessandro, Taylor, Patrick C., Garcia-San Martin, Lorea, Douville, Herve, Duveiller, Gregory, Forzieri, Giovanni, Swingedouw, Didier
• Format: Text
• Language: English
• Published: 2019
• Subjects: Arctic; albedo; Sea ice
• Online Access: https://doi.org/10.5194/tc-2019-283; https://tc.copernicus.org/preprints/tc-2019-283/

Clouds plays an important role on the climate system through two main contrasting effects: (1) cooling the Earth by reflecting to space part of incoming solar radiation; (2) warming the surface by reducing the Earth’s loss of thermal energy to space. Recently, scientists have paid more attention to the warming role of clouds because of the acceleration of Arctic sea ice melting and because of recent studies that did not find any response of cloud cover fraction to reduced sea ice in summer. On the contrary, with this work based on satellite CERES data and 32 CMIP5 climate models, we reveal that the cooling role of clouds is dominant. Indeed, cloud dynamic occurring in combination with sea-ice melting plays an important cooling effect by altering the surface energy budget in an apparently contradicting way: years with less sea ice are also those that show an increase of the radiative energy reflected back to space by clouds. An increase in absorbed solar radiation when sea ice retreats (surface albedo change) explains 66 ± 2 % of the observed signal. The remaining 34 ± 1 % are due to the increase in cloud cover/thickness when sea ice retreat and associated reflection to space. This interplay between clouds and sea ice reduces by half the increase of net radiation at the surface that follows the sea-ice retreat, therefore damping the impact of polar sea ice loss. We further highlight how this process is mis-represented in some climate models.