Research and/or Teaching Area: Understanding the climate change of the last century and predicting the response of Earth's climate to anthropogenic forcing requires a strong understanding of the character and the physical origin of natural climate variability.

My research focuses on how to separate natural climate variability from human-induced climate change in the observational record. Currently my work focuses on problems in the interpretation of two records of past climate variability -- high-latitude tree rings and a biological tracer of past climate found in ocean-bottom sediment cores. Analysis of tree rings have been used to argue that the warming of the last half-century is unprecedented in at least the last thousand years. However many of these same tree rings fail to capture the warming of the last half-century, calling into question whether they may also have failed to fully capture past warm epochs. Over longer timescales, different methods or inferring marine climate variability give radically different pictures of ocean climate variability over the last 8000 years. These different pictures of the Earth's past variability imply very different pictures of what the future of Earth's climate may look like.