Climate Feedbacks

The role of surface albedo feedback in climate

Here we evaluate the role of surface albedo feedback in climate by comparing 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 CO₂-doubling experiments were performed with both models to assess the impact of this feedback on equilibrium response to external forcing. This figure shows the surface warming in the two experiments broken down by season (VA=with surface albedo feedback, FA=without surface albedo feedback). Consistent with previous studies with simpler models, surface albedo feedback 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. Local internal surface air temperature anomalies in the extratropics are typically only 5-10% larger when surface albedo feedback is present. The main reason for this relatively weak signal is that the internal anomalies are not geographically coherent, and so horizontal damping processes dilute the impact of surface albedo feedback. This effect is readily apparent in this figure, showing the ratio (VA/FA) of temperature variability for local internal anomalies and extratropical-mean internal anomalies in the left two bars of each panel, and the ratio of extratropical warming when CO₂ is doubled in the right bar. As the spatial scale of the temperature anomaly increases from local to extratropical mean to global, the impact of surface albedo feedback increases dramatically.

In this study we also showed that when snow albedo feedback in northern hemisphere continents is isolated from horizontal damping processes, it has a similar strength in the CO₂-doubling and internal variability contexts. As seen in this figure, a given temperature anomaly in these regions produces approximately the same change in snow depth and surface albedo whether it was externally-forced or internally-generated. This suggests the snow pack's thermodynamic response time is fast enough that the behavior of snow albedo feedback in the context of present-day variability may provide information relevant to its behavior in climate change. In a later study, we take advantage of this fact to constrain simulations of snow albedo feedback in future climate by evaluating it in the context of the present-day snow and temperature variations.

Download the publication (Hall 2004) describing these results in more detail.