Basic Information

Although the world's oceans may indeed appear virtually limitless, the rapid and unprecedented rise in atmospheric CO2 levels since the Industrial Revolution may be pushing these vast bodies of water to their physiological limits. The burning of fossil fuels, deforestation, and other human-activities that contribute to climate change could dramatically alter Earth's oceans, perhaps within the next 20 years. Oceans cover two-thirds of the world's surface area and support the greatest diversity of life on Earth. The world's oceans are its most important storehouses of carbon, sequestering an estimated total of 40,000 billion tons of the greenhouse gas. This natural capacity is truly extraordinary, especially given that the atmosphere and landmass combined sequester approximately 3,000 billion tons.

According to the Intergovernmental Panel on Climate Change, the same forces that contribute to surface temperature increases are likewise warming the oceans. From the period between 1961 and 2003, global ocean temperature rose .10° C, or .18° F, from the surface to a depth of 700 meters. This change represents an average across the entire ocean, so both regional and temporal variations exist. The Atlantic Ocean accounts for the most significant change. Many scientists believe warmer ocean temperatures lead to more intense tropical storms and hurricanes, although the data are still uncertain.

One major and alarming consequence of ocean warming is clear. Coral reefs are dying all over the world, in a process known as "coral bleaching." Corals are tiny animals that live in immense colonies and harvest nutrients from a particular type of algae that inhabits their cells. Together, coral and algae create limestone reefs that provide habitat and food for a vast array of life; they make up one of the most productive ecosystems on Earth. The symbiotic relationship between coral and algae, however, is highly sensitive to temperature fluctuations. If temperatures rise above the coral's physiological thresholds, the algae die, leaving the coral without color or its source of nutrients. Corals can recover from short-term bleaching, but extended bleaching ultimately leads to mortality. In 1998, when the warmest ocean temperatures on record were measured, the oceans also experienced a massive coral die-off. Dead coral reefs will take decades or even centuries to recover, if they can recover. Dying coral communities will be accompanied by losses in marine biodiversity, shoreline protection, fisheries, and medicinal products.

In addition to the fisheries lost as an impact of coral bleaching, fisheries are disappearing in other regions due an increase in ocean "dead zones," another phenomenon linked to climate change. Earth is experiencing more intense winds, which cause an upwelling in nutrient-rich waters from the deep sea. When this nutrient-rich water reaches the sunlight, ocean plants known as phytoplankton bloom in great numbers. These tiny plants exist at the bottom of the food chain and provide food for small fish and shellfish. Yet when more phytoplankton bloom than fish can consume, they die and drift to the ocean floor, where bacteria decomposes them. The process of decomposition causes "hypoxia," or oxygen depletion in the water. Fish and shellfish that cannot escape hypoxic water suffocate from lack of oxygen and die. While ocean dead zones have been documented since at least the mid-nineteenth century, studies suggest their frequency and duration are increasing, and new regions are experiencing the phenomena. A new dead zone, for example, has recently arisen off the coast of Oregon and northern California, in an area once renowned for its fisheries.

In addition to raising ocean water temperatures, global warming is also causing the rapid and unprecedented acidification of Earth's oceans. Approximately 50 percent of the carbon emitted from the burning of fossil fuels and other anthropogenic activities over the last 200 years now resides in our oceans. This massive carbon influx has not occurred without consequences. When carbon dioxide is taken up by seawater, carbonic acid is formed. Some of this carbonic acid is neutralized by other components of seawater; however, the overall effect is acidification. Since the Industrial Revolution in the eighteenth century, the pH of surface seawater has decreased 0.1 units, equivalent to a 30 percent increase in hydrogen ions. This change represents a considerable acidification of the oceans and decreases seawater's subsequent ability to absorb more carbon in the future. While the process of ocean acidification is well understood, its consequences are not. Scientists do know that acidification will adversely affect the process of calcification, the process by which animals such as corals and mollusks form plates and shells from calcium carbonate. Because such creatures are near the bottom of the food chain, their survival is fundamental to the overall health of Earth's oceans.

One of the most widely known and well-documented consequences of a shifting climate is sea-level rise-an impact already apparent in many Alaskan coastal villages. Sea-level rise is the result of thermal expansion (water expands as it warms) and the loss of land-based ice, including glaciers and permafrost, as temperature rise. According to the IPCC's 2007 report, the ocean rose 1.7 mm per year throughout most of the Twentieth Century. That rate has nearly doubled since 1993, when satellite imagery revealed an increase of nearly 3 mm per year. This rate is not uniform across all regions; in fact, sea levels are projected to decline in some regions. Conversely, the U.S. Environmental Protection Agency reports that Atlantic Coastal water rose five to six inches above the global average. Alaska, too, is experiencing dramatic land loss. Higher seas will erode shorelines; cause saltwater encroachment into inland water sources, including aquifers and creeks; and result in more frequent flooding. The IPCC suggests that rising sea levels could convert 33 percent of Earth's wetlands to open water-destroying a key ecosystem for many plant and animal species, along with nutrient uptake and water filtration capacity. Scientists suggest that storm surges will become more severe as the climate changes. This impact will be exacerbated by the eroded shoreline.

Changes in the world's oceans will have serious and likely devastating effects on low-lying coastal communities around the world. The plight of the Native Alaskans of the tiny communities of Newtok and Kivalina has garnered worldwide attention. Yet the residents of Newtok, Kivalina, and other Alaskan villages are certainly not the only people at risk of the effects of climate change. The Florida coasts are renowned for their extensive, gently sloping beaches that create wide expanses of white sand. Yet models predict that sea levels could rise 8 to 30 inches in the region, which would result in a shoreline loss of hundreds of feet. This encroachment would extend beyond the beach and have severe effects for the region's tourism and agricultural industry.

Further, saltwater encroachment into low-lying areas would likely seep into underground aquifers and contaminate water used for municipal, commercial, and agricultural uses. Both the Hollywood and Big Cypress reservations of the Seminole Tribe, as well as Miccosukee tribal lands, are located in the Everglades region, where land elevation averages about one foot above sea level. This region is likely to be affected by rising seas and is at great risk for severe flooding, both from the rise itself and from intense storm surges. Sea level and weather changes, as well as saltwater encroachment, also threaten the plants and animals on which these tribes rely for their traditional lifestyles.

Earth's hydrologic cycle creates a close bond between the sea and freshwater sources. Changes in the ocean will impact the availability of potable water for tribal communities throughout the United States. Oceanic impacts will not be confined to coastal areas, though communities along our coasts will be the first to experience the impacts of these changes. Tribes who rely on marine mammals, fish, and shellfish for subsistence, and who are most at-risk for severe storm surges, erosion, and sea-level rise, will be forced to confront some of the most immediate, severe, and abrupt impacts of Earth's changing climate.

  1. Intergovernmental Oceanic Commission of UNESCO Scientific Committee on Oceanic Research. "Watching Brief: Ocean Carbon Sequestration, Ocean Storage." Available online at [accessed 5 December 2008].

  2. Bindoff, N.L., J. Willebrand, V. Artale, A, Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. Le Quéré, S. Levitus, Y. Nojiri, C.K. Shum, L.D. Talley and A. Unnikrishnan. 2007. "Observations: Oceanic Climate Change and Sea Level." In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

  3. U.S. Department of State. 5 March 1999. "Coral Bleaching, Coral Mortality, and Global Climate Change. Released by the Bureau of Oceans and International Environmental and Scientific Affairs, U.S. Department of State." Available online at [accessed 5 December 2008).

  4. The Royal Society. June 2005. "Ocean acidification due to increasing atmospheric carbon dioxide." Available online at [accessed 6 December 2008].

  5. Ibid.

  6. Bindoff, N.L., et al. 2007.

  7. U.S. Environmental Protection Agency. 19 August 2008. "Costal Zones and Sea Level Rise." Available online at [accessed 6 December 2008].

  8. Hanna, J.M. 19 September 2007. "Native Communities and Climate Change: Legal and Policy Approaches to Protect Tribal Legal Rights." A report published by the Natural Resources Law Center at the University of Colorado Law School in conjunction with the Western Water Assessment of the University of Colorado. Available online at [accessed 4 December 2008].