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 6000 years (at ~ 3.6 mm/year for 2006–2015) and is accelerating. In this chapter, we discuss both the causes and implications of sea-level rise from the perspective of a cryospheric hazard. We also review the best estimates of sea-level rise and cryospheric mass change from a variety of monitoring techniques. The transfer of ice into the sea has contributed almost 50% of the sea-level rise since 1993 and exceeded the combined sea-level changes due to thermal expansion, changes in terrestrial water storage, and changes in ocean basin size since at least 2006. This cryospheric contribution to sea-level rise is split between the combined ice sheets of Greenland and Antarctica and the global population of about 215,000 glaciers. Over the last decade, the contribution from ice sheets has been increasing faster than that from glaciers. The societal effects of sea-level rise will be highly varied throughout the world, with some locations experiencing a sea-level fall, while others experience a sea-level rise several times the global mean. Perhaps counterintuitively, 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 timescale than many of the other hazards discussed in this volume, the ramifications of sea-level rise will likely be more widespread and profound. Some of the most important implications discussed here include coastal inundation, increased coastal flood frequency, and groundwater salination