The Role of Surface Albedo Feedback in Internal Climate Variability, Transient Climate Change, and Equilibrium Climate Sensitivity

A coarse resolution coupled ocean-atmosphere simulation where surface albedo feedback is artificially suppressed by prescribing surface albedo is compared to one where snow and sea ice anomalies are allowed to affect surface albedo, as the model was originally designed. Canonical CO -doubling experiments were performed with both models to assess the impact of surface albedo feedback on equilibrium climate response to external forcing. Both models were also run for 1000 years without external forcing to assess the impact of surface albedo feedback on internal variability and compare it to the feedback’s impact on the response to CO -doubling. Sea ice albedo feedback behaves differently in the internal variability and CO doubling contexts. In contrast, snow albedo feedback in the northern hemisphere behaves very similarly; a given temperature anomaly in snow-covered 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 climate 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 represent the model’s snow albedo feedback in the CO -doubling context. This suggests the present-day satellite record could be used to estimate snow albedo feedback’s contribution to equilibrium climate sensitivity.