Present-day Climate Variability
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The present-day seasonal cycle of temperature is a prominent example of externally-forced climate variability. Just as water vapor and surface albedo feedback mechanisms can enhance the climate's sensitivity to increases in greenhouse gases (see future climate for a detailed discussion of these feedbacks), they also play a role in the climate's response to the annual variation of sunshine. For example, during summer, humidity levels are generally much higher than during winter. This means that the greenhouse effect is stronger in summer than winter. So part of the warmth of summer relative to winter is due to water vapor feedback. Surface albedo feedback also increases the amplitude of the seasonal cycle of temperature. Quantifying these effects and comparing them to the effects of feedback mechanisms on the climate's response to an increase in greenhouse gases is a major research goal of our group.

Feedback mechanisms also play a significant role in climate variations generated internally by the atmosphere-ocean system. For example, an unusually warm year in the northern hemisphere is often accompanied by decreased snow extent. The reduced surface albedo increases the absorbed sunshine, which makes the temperature even warmer. Similarly, water vapor feedback can amplify temperature anomalies generated internally by the climate system. In addition to understanding how these feedbacks affect internal climate variability, our research agenda in this area is to determine whether these feedbacks' impact on internal variability might provide crucial information about their role in the climate's response to external forcing.

Another research goal is understanding how modes of climate variability behave in the present-day climate. Examples of modes of variability include the El Nino phenomenon, the North Atlantic Oscillation, and its southern hemisphere counterpart, the Antarctic Oscillation. The main thrust of our research thus far has been on the Antarctic Oscillation and how it orchestrates oceanic and atmospheric variability in the southern hemisphere. We have also been examining how this mode responds to orbital forcing (see past climate for a detailed discussion of orbital forcing) with the goal of explaining paleoclimate variability in this region.

publications in this area

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