Sea Ice–Albedo Feedback and Nonlinear Arctic Climate Change

• Main Author: Michael Winton
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; Arctic Ocean; albedo; Climate change; Ice cap; Sea ice
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.143.5933; http://www.gfdl.noaa.gov/reference/bibliography/2008/mw0802.pdf

The potential for sea ice–albedo feedback to give rise to nonlinear climate change in the Arctic Ocean region, defined as a nonlinear relationship between polar and global temperature change or, equivalently, a time-varying polar amplification, is explored in the Intergovernmental Panel on Climate Change climate models. Five models supplying Special Report on Emissions Scenario A1B ensembles for the 21st century are examined, and very linear relationships are found between polar and global temperatures (indicating linear polar region climate change) and between polar temperature and albedo (the potential source of nonlinearity). Two of the climate models have Arctic Ocean simulations that become annually sea ice–free under the stronger CO 2 increase to quadrupling forcing. Both of these runs show increases in polar amplification at polar temperatures above −5°C, and one exhibits heat budget changes that are consistent with the small ice cap instability of simple energy balance models. Both models show linear warming up to a polar temperature of −5°C, well above the disappearance of their September ice covers at about −9°C. Below −5°C, effective annual surface albedo decreases smoothly as reductions move, progressively, to earlier parts of the sunlit period. Atmospheric heat transport exerts a strong cooling effect during the transition to annually icefree conditions, counteracting the albedo change. Specialized experiments with atmosphere-only and coupled models show that the main damping mechanism for sea ice region surface temperature is reduced upward heat flux through the adjacent ice-free oceans resulting in reduced atmospheric heat transport into the region. 1.