The main goal of our research is to understand what controls the sensitivity of the climate system to external forcing. A prime example of an external forcing is the observed increase in greenhouse gases due to human activity over the past century and the projected continuation of this trend over the next century. By understanding how much and in what ways this might be expected to alter climate, we can assess how much of the climate change over the past century is attributable to human activity, and how much the climate will continue to change over the next 100 years. External climate forcings can also be found in the distant past and may guide us in understanding the climate's sensitivity to greenhouse gas forcing. For example, we know that changes occurred in the amount and seasonal distribution of sunshine due to variations in the earth's orbit on time scales of tens of thousands of years. Is our prediction of the climate system's response to these external forcings consistent with the variations in climate seen in the observed record of past climate? If not, what are we missing in our current understanding of climate? Also, what direct analogies can we draw between the response of the climate to past external forcings and its response to future greenhouse gas forcing? And how are the two problems fundamentally different? Present-day climate variability may also contain information about the climate system's response to external forcing. For example, can we understand the climate's dynamical response to an external forcing in terms of its characteristic modes of internal variability? And is there information about the feedback mechanisms that control the climate's temperature response to external forcing in the signatures of internal variability?

Because of these relationships among past, present-day, and future climate variations, understanding climate sensitivity requires that we tackle past, present-day, and future climate problems. Click on one of these three categories to learn more about our research in that area.

Past Climate   <   Present-day Climate Variability   >   Future Climate