Science Briefs

Sea Level Rise

[Photo of waves crashing on a shore]

(Photo © 1978 Stephen P. Leatherman)

Sea level could rise 40 to 65 cm by the year 2100, due to predicted greenhouse-gas-induced climate warming. Such a sea level rise would threaten coastal cities, ports, and wetlands with more frequent flooding, enhanced beach erosion, and saltwater encroachment into coastal streams and aquifers. Therefore, it is important to study records of how sea level has been changing.

Sea level has fluctuated dramatically in geologic times. It was 2-6 m above the present level during the last interglacial period, 125,000 years ago, but 120 m below present during the last Ice Age, 20,000 years ago. In the last 100 years it has increased by 10-25 cm. However, future sea level is very difficult to predict, because not enough is known about how the ice sheets in Greenland and Antarctica will react to global warming. Furthermore, local sea level is affected by many regional processes, including tides, ocean currents, and geographically-varying land movements. These Earth motions are caused by ongoing adjustments of Earth's crust to the removal of the former ice sheets, tectonic deformation, subsidence of river deltas under sediment loads, and extraction of underground water, oil, or natural gas near the coast.

Vivien Gornitz has compared tide-gauge records and radiocarbon-dated geologic data from four widely separated regions, spanning a broad range of geologic settings, in order to remove any long-term geologic trends present in the recent instrumental records. Modern sea-level trends are found to be consistently 1-1.8 mm/yr higher than those derived from long-term geologic data. This result implies a recent acceleration of sea-level rise relative to the last few thousand years. This finding is compatible with other evidence for recent global warming, such as land and marine air temperature measurements, the worldwide retreat of mountain glaciers, subsurface borehole temperature profiles, and a northward migration of boreal forest-tundra boundary in northern Canada and Siberia.

Reference

Gornitz, V. 1995. A comparison of differences between recent and late Holocene sea-level trends from eastern North America and other selected regions. J. Coastal Res., Special Paper No. 17: Holocene Cycles: Climate, Sea Levels, and Sedimentation, pp. 287-297.

Contact

Please address all inquiries about this research to Dr. Vivien Gornitz.