What is Sea Level Rise?

Think and plan in terms of today’s storms and tomorrow’s tides.

– Peter Slovinsky, Maine Geological Survey

Sea level rise is a symptom of a warming planet.

The steady rise in global sea levels, recorded by tide gauges around the world, is due primarily to

  • the expansion of the oceans as they warm;
  • regional land subsidence (evident in parts of Atlantic Canada, where Nova Scotia has experienced roughly 7 inches (17 cm.) subsidence over the last century); and
  • water from melting glaciers and land-based ice sheets.

Sea levels will increase markedly in coming decades, but the rate of increase depends on how quickly the Earth warms and the melting occurs. According to the Intergovernmental Panel on Climate Change, “it is virtually certain that global mean sea level rise will continue for many centuries beyond 2100, with the amount of rise dependent on future emissions.”

sea level rise graph

Credit: climate.gov–Monthly global sea level from 1993 through early 2013 compared to 1993-2012 average, based on AVISO data. Graph adapted from Figure 2.1(x) in BAMS State of the Climate in 2012. 

Today’s more extreme high-tide events provide a glimpse into how our shorelines will be as sea level rises. In low-lying areas, a rise of one vertical foot (30 cm.) can cause the sea to move 100 feet (30 meters) or more inland. The University of Maine Climate Change Institute projects that over the next century, sea levels along the Maine coast—at the center of the Gulf of Maine—could rise 3-20 feet, and potentially far more depending on how much of the Greenland and West Antarctic ice sheets melt. Learn more about global sea rise.

In addition to direct flooding impacts (see next section), sea-level rise can cause inundation of wetlands, saltwater intrusion into drinking wells, and increased shore erosion.

More Resources on Sea Level Rise:

About Storm Surge and Flooding Damage

Flooding damage from sea-level rise is exacerbated by storm surge, when onshore winds cause water to pile up along the coast. Storm surge of 2 or 3 feet (0.6-0.9 meters) is relatively common in the Gulf of Maine, and can cause extensive damage when it coincides with high tide. “There’s only about a one-foot difference between ‘10-year’ and ‘100-year’ storm events,” notes coastal geologist Peter Slovinsky, “so a one-foot rise in sea level will cause ‘100-year’ events to occur about every 10 years.”

GOM-inundation

Credit: Clean Air-Cool Planet (now part of the UNH Sustainability Institute)

Flooding and erosion during high tides and storm events could cause extensive damage to shorefront properties, transportation and shipping infrastructure, and coastal ecosystems—like sensitive marsh habitats, seabird nesting islands and dunes.