Polar amplification in a coupled climate model with locked albedo

In recent years, a substantial reduction of the
sea ice in the Arctic has been observed. At the same time,
the near-surface air in this region is warming at a rate
almost twice as large as the global average—this
phenomenon is known as the Arctic amplification. The role
of the ice-albedo feedback for the Arctic amplification is
still a matter of debate. Here the effect of the surfacealbedo
feedback (SAF) was studied using a coupled
climate model CCSM3 from the National Center for
Atmospheric Research. Experiments, where the SAF was
suppressed by locking the surface albedo in the entire
coupled model system, were conducted. The results reveal
polar temperature amplification when this model, with
suppressed albedo, is forced by a doubling of the atmospheric
CO2 content. Comparisons with variable albedo
experiments show that SAF amplifies the surface-temperature
response in the Arctic area by about 33%, whereas the
corresponding value for the global-mean surface temperature
is about 15%. Even though SAF is an important
process underlying excessive warming at high latitudes, the
Arctic amplification is only 15% larger in the variable than
in the locked-albedo experiments. It is found that an
increase of water vapour and total cloud cover lead to a
greenhouse effect, which is larger in the Arctic than at
lower latitudes. This is expected to explain a part of the
Arctic surface–air-temperature amplification.