Letters: Sea-Level Rise by 2100

In his news and analysis piece reporting on the newly released fifth assessment report (AR5) by Working Group I (WGI) of the Intergovernmental Panel on Climate Change (IPCC) ("A Stronger IPCC Report," 4 October, p. 23), R. A. Kerr highlights three fundamental conclusions about climate change that were assessed with equal or greater confi dence than in previous IPCC reports. He also points to three "contentious points" on which he states that the AR5 "took a moderate line." Kerr includes sea-level projections among these points, and reports "a rise of 40 to 60 centimeters by late in the century and a worst case of 1 meter by 2100, [which is] higher than in 2007 but far below the meter or two of sea-level rise that some expect." As the authors of the IPCC WGI AR5 chapter on "Sea-Level Change," we wish to clarify that for the highest emission scenario considered (RCP8.5), the AR5 reported a "likely" range of 0.45 to 0.82 m for sea-level projections for the late 21st century (average over 2081 to 2100) and of 0.52 to 0.98 m by 2100. The difference in sea level between these two periods is large because in 2081 to 2100, the "likely" rate of rise is 8 to 16 mm per year, which is up to about 10 times the average rate of rise during the 20th century.