Covering more than 70% of our planet’s surface, the world’s oceans absorb more than 90% of the heat trapped in our atmosphere. As the concentration of greenhouse gases circulating in the atmosphere increases, more heat is absorbed by the ocean and the effects ripple outward. The volume of seawater expands, glaciers and polar ice sheets melt, and sea levels ultimately rise. Scientists estimate that 40% of sea-level rise over the past 35 years is due to global warming (1).
This graph shows how historical tide gauge data (blue) and satellite altimeter readings (red) can be used to estimate rates of sea level rise. Tide gauge data were collected by the Permanent Service for Mean Sea Level at the National Oceanographic Center in Liverpool, UK. Satellite altimeter data were collected during the Topex/Poseidon, Jason-1, and OSTM/Jason-2 missions starting in 1993. Source: Church and White, 2011
Is the change in sea-level measurable enough to notice? Yes! While the changes are not immediate, like when a storm tears sand away from the dunes, you can see from the graph on the right that global sea levels have risen at a rate of 0.06 inches per year, for a total of 8 inches since 1880 (see graph). But if you focus only on the past 30 years, sea levels have been rising nearly twice as fast, at a rate of 0.12 inches per year (2). At this rate, sea levels are projected to rise an additional 1 to 4 feet by 2100 (1).
Rates of sea level rise can also vary regionally, depending on the geography of an area, the rate of land subsidence, and ocean circulation patterns. In the Mid-Atlantic region, sea levels are rising more quickly than the global average, up to 0.17 inches per year (3).
Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merrifield, G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer and A.S. Unnikrishnan, 2013: Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
Williams, S.J., B.T. Gutierrez, J.G. Titus, S.K. Gill, D.R. Cahoon, E.R. Thieler, K.E. Anderson, D. FitzGerald, V. Burkett, and J. Samenow, 2009: Sea-level rise and its effects on the coast. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 11-24.