Sea Ice–Albedo Feedback and Nonlinear Arctic Climate Change - Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications - page 116

Plate 4 (top) shows surface albedo for the polar region as
a function of time for the two model experiments. The sea-
sonal ice state is indicated by the albedos for three months:
March (blue), June (green), and September (red). The annual
effective albedo (light blue) characterizes the time mean re-
flective capacity of the ice pack. The NCAR model loses
its September sea ice near year 50; the MPI model loses it
later, at about year 100. Both models have a progression of
albedo reductions moving to earlier months in the sunlit sea-
son over the course of the integrations. The March sea ice is
lost abruptly in the MPI model in the CO 2 stabilized period.

The March decline is more gradual in the NCAR model. The
variability of March albedos after the decline indicates oc-
casional reappearance of ice in the NCAR model but not in
the MPI model.
Plate 4 (bottom) shows the albedos as a function of polar
region surface air temperature. The albedo changes are more
similar when viewed as a function of temperature rather than
as a function of time, but differences remain. The MPI model
albedo declines are more abrupt in temperature as well as in
time. Both models become seasonally ice free (the Septem-
ber albedo flattens) at an annual polar temperature of about

Figure 1. (top) Polar surface albedo feedback in three temperature eras. (bottom) Monthly contribution to polar surface
albedo feedback for surface temperatures less than −5°C (dashed) and between -5 and 0°C (solid) for the NCAR CCSM3
(black) and MPI ECHAM5 (gray) models. All data have been boxcar filtered over a 5-year period.