Journal of Climate 2014 ; e-View
doi: http://dx.doi.org/10.1175/JCLI-D-14-00389.1
Assessment of sea-ice albedo radiative forcing and feedback over the Northern Hemisphere from 1982 to 2009 using satellite and reanalysis data

Yunfeng Cao,1,2 Shunlin Liang,1,2 Xiaona Chen,1,2 and Tao He2
1 State Key Laboratory of Remote Sensing Science, and College of Global Change and Earth System Science, Beijing Normal University

2 Department of Geographical Sciences, University of Maryland 

Abstract
The decreasing surface albedo caused by continously retreating sea ice over Arctic plays a critical role in Arctic warming amplification. However, the quantification of the change in radiative forcing at top of atmosphere (TOA) introduced by the decreasing sea ice albedo and its feedback to the climate remain uncertain. In this study, based on satellite-retrieved long-term surface albedo product CLARA-A1 and radiative kernel method, an estimated 0.20 ± 0.05 W m-2 sea ice radiative forcing (SIRF) has decreased in the Northern Hemisphere (NH) owing to the loss of sea ice from 1982 to 2009, yield a sea-ice albedo feedback (SIAF) of 0.25 W m-2 K-1 for NH and 0.19 W m-2 K-1 for the entire globe. These results are lower than the estimate from another method directly using the Clouds and the Earth’s Energy (CERES) broadband planetary albedo. Further data analysis indicates that kernel method is likely to underestimate the change in all-sky SIRF because all-sky radiative kernels mask too much of the effect of sea ice albedo on the variation of cloudy albedo. By applying an adjustment with CERES-based estimate, the change in all-sky SIRF over NH was corrected to 0.33 ± 0.09 W m-2 , corresponding to a SIAF of 0.43 W m-2 K-1 for NH and 0.31 W m-2 K-1 for the entire globe. We also determine that relative to satellite surface albedo product, two popular reanalysis products - ERA-Interim and MERRA, severely underestimate the changes in NH SIRF in melt season (May to August) from 1982 to 2009 and the sea ice albedo feedback to warming climate.

Corresponding author: Yunfeng Cao, College of Global Change and Earth System Science, Beijing Normal University, No. 19 Xinjiekou Wai Street, Haidian District, Beijing, China, 100875 (willingcao@gmail.com)