My main research interest lies in understanding the variability of the climate, both its internal variability and the response to external forcing. In particular, how changes related to varying forcings relate to variations due to intrinsic (unforced) climate variability such as oscillations in the ocean's deep thermohaline circulation that affect ocean heat transports or atmospheric modes of variability like the North Atlantic Oscilation. I mainly use large-scale general circulation models for the atmosphere and ocean to investigate these questions.
The evidence of long term paleo-climate variability exists primarily in the form of proxy data recorded in deep sea cores, ice cores, tree rings and other proxies such as the the skeletal remains of corals or in speleothems (cave deposits). Much of my recent work has focussed on ways to approriately compare the paleo-data with models. The main difficulty is that the proxy data are records of multiple processes and hence, it is difficult to unambiguously ascribe a climatic cause to any particular recorded event.
Please visit my NASA/GISS page for more detail on specific research projects.