My research interests focus on some fundamental questions about the behavior of the climate system. How sensitive is the Earth's climate to external forcing? Is abrupt change a characteristic of the climate? What are the mechanisms of climate change? Several of these questions arise out of the paleoclimate record. In addition to observed major swings in global ice volume over the past 600,000 years (the so-called “Ice Ages”), there are superimposed abrupt changes that can happen on the order of decades. The paleoclimate record gives us an idea of the dramatic range of climate behavior that is “natural.” It is essential to understand the mechanisms behind these changes in order to put our present climate into the proper context, and to understand and predict how the climate may change in the future as anthropogenic greenhouse gases increase.
To address these questions, I use mathematical models of the climate. These range in complexity from one-dimensional approximations of the climate to global, three-dimensional models (general circulation models- GCMs). My focus has generally been on the tropical coupled ocean-atmosphere system, and in particular on the El Niño/Southern Oscillation (ENSO). As the largest mode of variability in the modern climate, understanding the whys and hows of past changes in (ENSO) are essential in answering fundamental questions about the behavior of the climate system, and are highly relevant for addressing the problem of how climate may change in the future.