COG3

Future climate change: clues from the past

Earth system sensitivity (ESS) is the global temperature response to doubled CO2 that includes both slow and fast feedbacks. The geologic record is well suited for calculating ESS owing to the longer timescales that it captures. ESS has some relevancy for present-day climate policy because, unless carbon sequestration activities ramp up drastically, the current level of anthropogenic warming will persist for at least 103-104 years. This sluggish response increases the odds that the slow feedbacks captured by ESS (e.g., continental ice sheet dynamics) will manifest themselves. I will present a variety of geologic studies that suggest a high ESS (>3 degrees C) during both icehouse and greenhouse times. The ice-albedo feedback is likely responsible for the high ESS during icehouse times, but the factors responsible for a high ESS during greenhouse times remain enigmatic. Revealing these ‘hidden’ greenhouse feedbacks is of growing importance for understanding the consequences of our currently warming planet.