Ice Sheets, Glaciers, and Sea Level

Within the past 125,000 years, variations in Earth’s climate have resulted in global sea levels fluctuating from 130 to 140 m lower than present day to 6 to 9 m higher. Presently, global mean sea level is rising at its fastest rate in the past 6,000 years (~3 mm/year). In this chapter, we discuss both the causes and implications of sea-level rise from the perspective of a cryospheric hazard. We also survey the best estimates of sea-level rise and cryospheric mass change from a variety of monitoring techniques. The transfer of terrestrial ice into the sea has contributed about 50 percent of the sea-level rise since 1993, and probably exceeded the combined sea-level changes due to thermal expansion, changes in terrestrial water storage, and changes in ocean basin size since 2003. This cryospheric contribution to sea-level rise is approximately equally split between the combined ice sheets of Greenland and Antarctica, and the global population of about 200,000 glaciers. The societal effects of sea-level rise will be highly varied throughout the world, with some locations experiencing relative sea-level drop, whereas others experience a relative sea-level rise several times the global mean. Perhaps counter-intuitively, the sea-level rise due to terrestrial ice loss will be most substantial in areas furthest from the source of melting ice. Although this cryospheric hazard will unfold over a much longer time scale than many of the other hazards discussed in this volume, the ramifications of sea-level rise will likely be more widespread and profound. Some implications discussed here include coastal inundation, increased coastal flood frequency and groundwater salinization.