David Helfand

Columbia University, Chair

Global Warming: What We Know and What We Don't Know

On the subject of Global Warming, everyone is finally paying attention, but misinformation is rampant. I will provide a dispassionate analysis of the situation as it is understood by the best science of today, categorizing the influences on Earth's climate as 1) those which are predictable, measured, and understood (e.g., changes in Earth's orbit), 2) those which are predictable, measured, and only partially understood (e.g., the buildup of greenhouse gases in the atmosphere), and 3) those which are unpredictable, poorly measured, and not well understood at all (e.g., ocean circulation). I place the problem in the context of the highly accurate measurements we have collected on the long-term history of past climate, and emphasize how uncertainties arise in predictions of future climate as a consequence of complicated feedback loops in the climate system. I briefly assess the likely impact of climate change on ourselves and our grandchildren, and, in what I anticipate to be a lively question and answer period, address the issue of whether anything can reasonable be done to regulate the Earth's climate.