Human Dimensions of Global Warming

Rising Sea Levels


As sea level rises, it pushes inland. How far it penetrates depends on several factors. Sea level rising along a flat-lying coastline can push far inland, whereas sea level rise on a steep shoreline makes little appreciable difference. If coastal land is sinking for tectonic reasons, sea level rises faster, but if the land is rising due to Earth movements, sea level might actually fall. Local coastal currents can also make a difference, enhancing or suppressing sea level rise caused by climate change. Along the Mid-Atlantic coastline from about New York City to Cape Hatteras, North Carolina, the combination of climate change-induced sea level rise, a rapidly sinking coastline, coastal currents that reinforce sea level rise, and a very broad, flat coastal shelf results in relative sea level rise that is about twice the global average.

Graph of sea level rise predictions for 2100. IPCC: .6-1.9 ft. Rahmstorf: 1.6-4.6 ft. Pfeffer et al.: 2.6-6.6 ft
Figure 9.2: Observed and predicted sea level rise. There is a strong consensus in the scientific community that the 2007 IPCC estimates of 21st century sea level rise are far too low. Observations in the first decade of the century support that view. Most experts think the projections of Rahmstorf are more likely. Optional: read an article update on Rahmstorf's projections.
Credit: Copyright ©2009 Jeff Masters. Used with permission.

There are many physical impacts caused by sea level rise that are observed today. As ocean water pushes inland, it increasingly inundates the coastal zone. The pressure exerted by the rising sea pushes saltwater further upriver and causes saltwater to intrude into coastal aquifers, degrading water quality and sometimes making water unfit for human use. When storms strike the coastline, they are working from a higher baseline, so waves and storm surges penetrate further inland, causing more damage than before. The greater penetration of waves results in increased coastal erosion. Coastal ecosystems have evolved to migrate inland as sea level rises, but because the rate of sea level rise is so rapid, some ecosystems cannot migrate fast enough. Of the ecosystems that can respond to rapid sea level rise, many confront barriers erected by nature or, more likely, by humans; roads, buildings, and other structures effectively squeeze migrating ecosystems, barring them from escaping the rising seas.

Image of the flooding in a city with a car underwater in the street. Armored and raise police vehicle drive through water
Flooding in Italy.