Climate models generally exhibit a poleward amplification of the surface air temperature increase that occurs in response to increased greenhouse gas levels. However, observational evidence of polar amplification during the 20th century is ambiguous, leading some to question the models' sensitivity. Furthermore, the wide range of high latitude sensitivity among models suggests disagreements remain regarding the physical processes responsible for poleward amplification. By means of this collaborative research project, the PIs will conduct a study to improve understanding of poleward amplication. A number of candidate feedback processes, including ice-albedo feedback, might affect high latitude climate sensitivity, and they will evaluate their relative impacts. Their approach is to perform sensitivity studies with one climate model, and to compare model sensitivity when the same sea ice component model is implemented in three different climate models. They will also analyze polar climate variations in a 15-member ensemble of 20th century simulations to explore possible attribution to internal variability or external forcing. They will also compare simulated and observed polar amplification. They plan to use the Community Climate System Model (CCSM) for much of the study, and compare the polar climate sensitivity of CCSM to the sensitivities of two other models, one from the Geophysical Fluid Dynamics Laboratory (GFDL) and the other from the Hadley Centre for Climate Prediction and Research. Together, these three models exhibit a wide range of polar amplification and global climate sensitivity. With their collaborators at these institutions, they plan to evaluate the role of sea ice physics in polar climate sensitivity by implementing the sea ice component from CCSM into the other two models. Then they will evaluate to what extent the range of sensitivity among the models depends on sea ice physics.
Developing partnerships among modeling centers is a necessary step towards better understanding and simulation of polar climate sensitivity. This collaboration brings together scientists at the University of Washington, the University of California at Los Angeles, the National Center for Atmospheric Research, GFDL, and the Hadley Centre. The project will also support graduate students, who will be encouraged to visit modeling centers and attend conferences and workshops. In addition, results from this project will influence courses taught by the PIs. Finally, the simulations will be available immediately to all members of the CCSM Polar Climate Working Group, which is open to anyone.
