Proceedings of the National Academy of Sciences, published online before print December 15, 2009; doi: 10.1073/pnas.0912878107. PNAS (December 22, 2009),Vol. 106, No. 51, pp. 21461-21462.

Jonathan T. Overpeck* and Jeremy L. Weiss

University of Arizona, Tucson, AZ, U.S.A.

Few of the possible impacts of future climate change have captured more public attention than sea-level rise. Globally, sea-level rise has accelerated since the 19th century, driven primarily by the expansion of warmer oceans and melting glaciers, along with a modest transfer of water into the ocean from the Earth's polar ice sheets. The observed rate of sea-level rise has not been uniform around the globe because of regional factors, but there is no doubt that the average sea-level trend is upwards (1). Implications for the rates and magnitudes of future sea-level rise are less clear, and a new study in this issue of PNAS (2) provides useful insight into how sea level will change through this century and beyond.

There are two main types of sea-level information needed to inform the development of effective climate change policy. First are estimates of the sea-level rise expected in the relative near term, namely by the end of the century. Second are estimates of the sea-level rise that will occur further into the future over many centuries as ice sheets and oceans come into equilibrium with a warmer atmosphere.