Coastline Changes from Melting Ice Sheets

Comiso and Parkinson reply: Lasse Kivioja is correct that deglaciation leads to isostatic adjustments that would affect sea level, that these adjustments would vary regionally, and that full melting of the Greenland ice sheet would take considerable time. However, the 7.2-m estimated sea-level rise for a full deglaciation of Greenland is the same value tabulated by the Intergovernmental Panel on Climate Change, with the specific indication that “sea level rise equivalent is calculated with allowance for isostatic rebound.” 1 Any such estimates involve approximations and sizable error bars, but the 7.2-m value should be correct at least to first order.

We agree with Jose Ortiz de Zarate that for people with oceanfront property, practical information in the form of quantitative predictions would be very desirable. The point of our article, however, was to summarize recent satellite-observed changes in the Arctic. Accurate predictions require sophisticated coupled models of the ocean, atmosphere, and cryosphere system. Ortiz de Zarate might be interested in page 672 of reference ¹ , which presents maps of projected 21st-century sea-level changes resulting from thermal expansion and ocean circulation changes, with those projections based on coupled climate-model simulations. Also, imposing an anticipated temperature rise of 8 ° on an ice-sheet model, Anne Letréguilly and coworkers ² calculate a projected ice volume decrease of 68 500 km³ in Greenland and a sea level rise of 17 cm worldwide by 2100.