The warming climate is causing sea level to rise at an accelerating rate, and this is expected to continue, depending on human decisions about our energy system. Economic analyses generally show that efficient response to this challenge will be more favorable than ignoring the science and continuing with business as usual. Those analyses often assume that we will respond efficiently, and that the rise will be slow, small and expected. Recent events raise major questions about our efficiency, however, and scientific advances suggest that rapid warming could cause larger and faster rise than previously expected, with much higher costs. If so, then there is greater value in slowing warming and in managing coasts for resilience, and in advancing science rapidly to reduce the large uncertainties. Mrs. Hepsa Ely Silliman Memorial Lectures at Yale