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The Rise and Fall of the Oceans: What’s Next?

By: , Posted on: December 4, 2015

sea level
Source: Flickr

We live on a blue planet, 70% of which is covered by ocean. Marine biodiversity is concentrated in certain hot spots and ecoregions of global importance in the Earth’s oceans, most notably coral reefs. Oceans are under siege from the overharvesting of natural resources, pollution, habitat destruction, invasive species, and climate change. Projected sea level rise and the collapse of commercial fisheries are putting food supplies and coastal areas at risk, potentially leading to economic and social upheaval. A marine commons is needed to enact new policies that establish marine protected areas, sustainably managed fisheries, and that prepare coastal communities and island nations for rising sea level and storm surges of the 21st century.

Sea level (the average height of the ocean surface measured from mean high to mean low tide) has been moving up or down for millennia via thermal expansion or contraction of the oceans, from atmospheric influences, and the melting or expansion of terrestrial ice sheets and glaciers (“Sea Level Rise and Coastal Ecosystems, Sea Level Rise and Health“). When sea level drops, the geography of the planet changes through the creation of land bridges such as the Bering Land Bridge that connected Asia to North America during various Pleistocene ice ages and permitted ancestral humans, woolly mammoths, and other plants and animals to migrate between continents. In this case, biogeography is linked to the cooling or warming of the atmosphere. While ancient sea level changes were gradual, modern sea level rise is poised to happen extremely rapidly. This sea level rise is human caused, and there are human-caused barriers (like cities and other developments) that will block the migration of wildlife in search of more suitable climate space.

Read More on this Topic: The Disturbing Truth about the Rise in Sea Level

Sea level rise due to climate change is difficult to accurately predict, but estimates range from 0.5 to 3 + m by century’s end (Sea Level Rise and Coastal Ecosystems; Sea Level Rise and Health) and it could be a lot worse if either the Greenland ice sheet melts down – releasing extraordinary levels of heat-trapping methane (a very dense greenhouse gas) — or the conveyor belt shuts down due to moderating oceanic temperatures. Nearly half of the world’s major cities are located within 50 km of the coast, and coastal population densities are 2.6 times larger than the density of inland areas. Cities like Mumbai, Shanghai, and New York may experience major economic damages (as recently occurred in the NY area from super storm Sandy). Island nations like the coral atoll of Funafati, Tuvalu (< 3 m above sea level) in the South Pacific are already experiencing sea level rise damages. Rising sea level is creating a social injustice issue whereby the richest and most polluting countries of the world disproportionately contribute to human demographic dislocations that are hardest felt in economically poor or disadvantaged nations like Tuvalu (Figure 1).

sea level trends
Figure 1: Global sea level rise 1992–2013. Source:


One Ocean and the Marine Commons

The One World – New Commons – theme resonates throughout the Global Change module – but perhaps is most urgently needed for the atmosphere and the oceans. These have been linked since the molten Earth began cooling eons ago and now need to be linked by humans in a way that stewards the planet’s finite and life-giving resources. In a true commons the atmosphere, oceans, and terrestrial environments are properly cared for because our survival depends on them. Sadly, in recent decades they have been treated as a place for off-loading the waste products of a boundless civilization. The oceans are especially vulnerable in this regard, as we obtain so much of their bounty and they give us so much in return by mitigating our climate.

If we are going to continue to reap the benefits offered by the world’s oceans, we need to reverse the decline of marine biodiversity while simultaneously “stabilizing” the global climate. For instance, the Pew Oceans Commission recently called for an enforceable national policy (USA) to protect, maintain and restore the health of marine ecosystems. The commission states that this will not only support economically and culturally valuable fisheries, but will also ensure recreational opportunities for the public and the protection of ecological services from the oceans.

Read more on this topic: Health Check on an Ailing Planet

If we truly care about the oceans, we need to stop treating them as a dump. More areas need to be protected from overfishing and habitat destruction, particularly in hot spots and other areas of global marine importance. Notably, only 1% of the world’s oceans are strictly protected, compared to about 12% of terrestrial areas. Many scientists recommend that 20–40% of the marine environment needs to be protected at some level. Studies also show that Marine Protected Areas provide a boost to local fisheries as they serve as a “source area” for marine productivity because of the low-levels of human disturbance. In addition, protection of coastal wetlands, like mangroves, and the development of new infrastructure is essential in adapting coastal cities to sea level rise. Responsibly managed fisheries, through certification programs such as the Marine Stewardship Council, offer incentives in market recognition for creating a sustainable fishery and consumer choices to support them (Figure 2).

sea level models
Figure 2: Historic, current, and projected sea level change. Tide gauge data are indicated in red and satellite data in blue. The grey band shows the projections of the IPCC Third Assessment report (Allison et al., 2009). A 1-meter rise could flood ~25–80% of the U.S. coastal wetlands and 5000–10 000 miles2 of dry-land. If West Antarctic Ice Sheet collapses, sea level would rise 5–6 m (17–20 feet). This could occur within a few centuries (IPCC, 2007).

But to be part of the atmospheric, marine, or global commons, we will need to restrict our marine, terrestrial, and global footprints through new policies that allow humans and marine ecosystems to both prosper.

Read more about the changing sea levels here.

This excerpt was taken from the article Oceans and Global Change: One Blue Planet. The article is included in the innovative Reference Module in Earth Systems and Environmental Sciences, a dynamic resource that combines thousands of interdisciplinary comprehensive and encyclopedic articles. The Reference Module is continuously reviewed and updated to keep you at the forefront of scientific discoveries. Click here to learn more!

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