SFU Royal Society of Canada Seminar Series: "Danger from the Sea -Sea-level rise in a changing climate"

Abstract

Changes in the level of the sea relative to the land occur on timescales differing by ten orders of magnitude, from a few minutes to thousands of years. Along many coastlines, daily and seasonal tidal changes override all other factors, with tidal ranges up to nearly 20 m in a few areas. Non-tidal fluctuations, however, are also important and include: 1) subsidence and uplift of the coastline during large earthquakes, 2) ephemeral changes in sea level associated with storm surges, 3) seasonal and decadal variations in sea level related to coupled atmospheric and ocean circulation (e.g. ENSO) and to fluctuations in atmospheric pressure, 4) global (eustatic) sea-level changes related to glacier volume changes, 5) changes in ocean water temperature and salinity (steric effects), 6) variations in the storage of water in reservoirs on land and within Earth's crust, and 7) long-term, slow changes in relative sea level associated with tectonism, sedimentation, and residual isostatic adjustment of Earth's crust following the retreat of the last continental ice sheet in northwest North America. The most important non-tidal factors, from a societal perspective, are those linked to climate. Global sea level is expected to rise between about 60 cm and 1.4 m by the end of the century due to warming of upper ocean waters and additions of meltwater from alpine and arctic glaciers, Antarctica, and Greenland. Towards the end of the century, the main sources of meltwater will be melting and calving of the Antarctic and Greenland ice sheets. The magnitude of sea-level rise will differ around the world, but given that eustatic sea level rise may increase from its current rate of a 3 mm a-1 to about 1 cm a-1 by the end of the century, no low-lying coastline will be unaffected. Erosion and flooding of low-lying coastal areas can be expected during rare extreme storms, especially when wind-driven ocean surges coincide with high tides or with strong storms. Flooding and erosion may be exacerbated by changes in storminess in the warmer climate that is anticipated later in the century. Unfortunately, sections of the world's coastline that are most vulnerable to flooding and erosion are those that support the largest human populations and infrastructure.