The Role of Surface Albedo Feedback in Climate

A coarse resolution coupled ocean-atmosphere simulation where surface albedo feedback is suppressed by prescribing surface albedo is compared to one where snow and sea ice anomalies are allowed to affect surface albedo. Canonical CO -doubling experiments were performed with both models to assess the impact of this feedback on equilibrium response to external forcing: It accounts for about half the high-latitude response to the forcing. Both models were also run for 1000 years without forcing to assess the impact of surface albedo feedback on internal variability. Surprisingly little internal variability can be attributed to this feedback, except in the northern hemisphere continents during spring and in the sea ice zone of the southern hemisphere at all times of year. At these locations and during these seasons, it accounts for at most 20% of the variability. The reason for this relatively weak signal is that other damping processes dilute the impact of surface albedo feedback. When snow albedo feedback in northern hemisphere continents is isolated from these other damping processes, it has a similar strength in the CO doubling and internal variability contexts; a given temperature anomaly in these regions produces approximately the same change in snow depth and surface albedo whether it was externally-forced or internallygenerated. This suggests the presence of internal variability in the observed record is not a barrier to extracting information about snow albedo feedback’s contribution to equilibrium climate sensitivity. This is demonstrated in principle in a ‘scenario run’, where estimates of past, present, and future changes in greenhouse gases and sulfate aerosols are imposed on the model with surface albedo feedback. This simulation contains a mix of internal variations and externally-forced anomalies similar to the observed record. The snow albedo feedback to the scenario run’s climate anomalies agrees very well with the snow albedo feedback in the CO doubling context. Moreover, the portion of the scenario run corresponding to the present-day satellite record is long enough to capture this feedback, suggesting this record could be used to estimate snow albedo feedback’s contribution to equilibrium climate sensitivity.