The Impact of Rising Seas

Ice caps are melting, ocean water is warming and expanding, and sea levels are rising. All scientific data, measurements, and models agree on these basic facts. Questions still remaining are how high will the seas rise, how fast will it happen, and what will the impact be on coastal communities?

Three recent studies shed some light on these questions. One study, published in the March 14, 2016, issue of Nature Climate Change, led by a University of Georgia demographer, predicts that up to 13.1 million people living in US coastal communities will be, by the year 2100, displaced by rising seas. The study estimates that with no protective measures, 4.9 million could be forced from the coast if seas rise 2.95 ft. (0.9m), and 13.1 million will have to vacate if seas rise 5.9 ft. (1.8m). The National Oceanic and Atmospheric Administration (NOAA) predicts that sea levels will rise between 8 in. (0.3m)¬†and 6.6 ft. (2m), depending on the speed and extent of polar ice melt. Both of the study’s scenarios fall within that range. The Southeastern US would be the area of greatest risk, with half the evacuations occurring in Florida.

Researchers at USGS published a paper in the same March 14 issue of Nature Climate Change stating that 70% of the northeast Atlantic coast has the capacity to change in response to rising seas: barrier islands may migrate inland and form protective dunes, new inlets may form. Tidal marshes can trap sediment and break down decaying plants into new soil, and build up the marshy terrain high enough to keep pace with sea level rise. This study predicts that most coastline communities from Virginia to Maine will not be submerged by sea level rise, but will adapt by forming natural barriers.

An article published in Proceedings of the National Academy of Sciences on Feb. 22, states that sea levels are rising at their fastest rate in 2,000 years. Measurements of past sea levels gathered at 24 sites around the world, and analysis of a 1.1-km (0.6 mi) core pulled from an Antarctic seabed, indicate that sea levels have been rising at a much faster rate in the past 100 years than at any time during the past 2 millennia. The seabed core analysis also shows that land-based ice sheets are vulnerable to the amount of CO2 in the atmosphere. In the past, the higher the parts-per-million of CO2, the faster the ice caps and glaciers melted. Currently, parts- per-million of CO2 register above 400, compared to the pre-industrial reading of 280. Millions of years ago, when hundreds of erupting volcanoes were changing the shape of the planet, parts-per-million spiked to 500, and ice sheets melted rapidly and retreated far inland. Ocean levels rose dramatically. If humans keep burning fossil fuels and pumping CO2 into the atmosphere at the present rate, a 500 ppm scenario could happen again.

Even with all the studies and climate models, no one knows for sure how fast these changes will take place. But if you live on or near the coastline, it’s best to help your community plan ahead for the changes that are sure to come.