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.
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.