Past Climate

The present-day geographical and seasonal distribution of sunshine is dictated by the geometry of the earth's orbit around the sun. This geometry changes on time scales of tens of thousands of years: the tilt of the earth's axis wobbles, the earth's orbit becomes more and less circular, and the time of year when the earth is closest to the sun varies. The changes in the geographical and seasonal distribution of sunshine associated with these variations in the earth's orbit are known as "orbital forcing", and are thought to be the main drivers behind most climate variability over the past million years, including the ice ages. Our work in this area involves examining the response of climate models to orbital forcing. In particular, we address the following questions: Does orbital forcing excite preferentially the modes of variability characteristic of the present-day climate system? How successful are current climate models in explaining the climate variations seen in the observed paleoclimate record? To the extent they are not successful, what physical mechanisms are missing from the models? And finally, what is the relationship between the climate's response to orbital forcing and its response to the greenhouse gas perturbation?

publications in this area

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