Paleoclimatic Perspectives on Climate Sensitivity to Carbon Dioxide

Our research strives to use the Earth's past climate history to help bracket the deep uncertainties in future climate predictions. We attempt to quantify estimates of past climate sensitivity from a collection of paleoclimatic proxy records. We have compiled a database of all the available sea surface temperature proxy records over the past 600,000 years, as well as the available greenhouse gas ice core records. We develop estimates of the numerous sources of uncertainty in these calculations and proxies to enable a robust uncertainty estimate in the final analysis. We estimate changes in radiative forcing from non-greenhouse gases using a rough approximation for temperature-albedo feedback, and a sensitivity analysis of our assumptions. Tentative, preliminary results suggest a most-likely climate sensitivity value of 4 K, and a probability distribution that seems to suggest less likely low- and high- end tails than seen in some recent modeling studies. Our research improves upon previous studies that often neglected key uncertainties in the proxy records and tended to focus on specific locations in space and time, rather than a more continuous global temperature analysis.