Sea Level Rise

In a warm, carbon-rich future, the global amount of continental ice sheets will be greatly reduced, if not gone completely, and the surface of the global ocean will warm.  If locations of deep-water formation, such as North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW), are greatly warmed, the formation of deepwater masses and the cooling and oxygenation of the deep ocean will decline.  This has the potential to greatly warm and thermally expand vast amounts of the deep global ocean.

Sea level rise due to climate change can occur via two mechanisms; the first is the volumetric expansion of water due to rising temperatures and the second is the addition of glacial melt water. Sea level change in the 21th century is predicted using satellite altimetry datasets and climate models that incorporate polar warming, glacial melt and deepwater warming. As the datasets and the models are further developed, scientists are refining their capacity to accurately predict how sea level rise will progress.

Based upon current constructions from the National Oceanographic and Atmospheric Administration global ocean mean sea level is rising at a rate of approximately 3.0 mm/year. In only the next 90 years, the global mean sea level has been predicted to rise by 1 meter. Throughout earth’s history, sea level has fluctuated greatly, in step with the glaciations of the polar latitudes, plate tectonics, and the rhythmic cycles driven by the earth’s rotation around the sun.  Sea level is not a static feature of our earth’s ocean.  But, like many of the processes occurring under anthropogenic climate change, the rapidity of modern sea level rise is of extreme concern to biological communities.  

Why does sea level rise threaten marine ecosystems?

Most marine communities show a great deal of community structure and organization at the sea’s surface. Coral reefs, sea grass meadows, kelp beds, rocky intertidal zones and estuarine communities; all of these valuable ecosystems are structured around sea level. Many of these shallow-water ecosystems are already imperiled by coastal development, eutrophication (the addition of heavy nutrient loads), and industrial pollution. These impacts reduce an ecosystem’s ability to recover and show resiliency in the face of novel change. Rapid sea level rise is an excellent example of the no-analogue predicament that marine ecosystems are currently facing.

There are many unanswered questions regarding what capacity organisms and ecosystems have to withstand rapid sea level change.  Particular populations stand out in their need for active conservation right now, in order to ensure their survival out of the 21st century.  Low-lying atolls and reef crests, and the animals that use these habitats for breeding, laying eggs or rearing young are immediately threatened by sea level rise.  Sea turtles, marine mammals (such as the Hawaiian Monk Seal), and open-ocean sea birds are a few of the organisms that use such habitats. Estuarine and freshwater deltas, mangroves and salt marshes are also threatened by rapid sea level rise. Countless mammals, plants, invertebrates and birds use such habitats.

Coastal areas provide critical ecosystem services to surrounding human communities and infrastructure.  They serve to reduce the wave energy that hits beach areas; they percolate and clean terrestrial runoff; and they function as nurseries for commercially important fisheries species. Therefore, rapid sea level rise not only threatens ecological systems, it also threatens coastal communities and economies.