CONSEQUENCES OF SYSTEM DESTABILIZATION DUE TO CLIMATE CHANGE

Affected Marine Ecosystems and Species

Global climate change, with its associated sea-level rise, increased air and water temperatures, and changes in precipitation patterns, is predicted to alter marine environments through a variety of direct and indirect impacts. Global climate change introduces new instabilities into systems that are already greatly disturbed and altered by over-exploitation. As a result, marine ecosystems are being simplified and becoming less stable and less productive in all climate zones⁴. Stressed ecosystems in turn are more vulnerable to disease, which in turn can push them closer towards collapse⁵.

The polar regions, too, will likely become warmer and wetter. In the Arctic, sea ice will continue to thin and retreat, to the extent that by 2050, sea-ice cover in the Arctic Ocean may be reduced to about 80 percent of the area it covered in the mid-twentieth century. Such sea-ice declines may well have negative repercussions for many species of marine wildlife, including seabirds and marine mammals: seal species, for example, that use the sea ice as a platform on which to rest, and polar bears that prowl the ice to prey on seals⁶. Similarly, in Antarctica, the ice sheet is melting far more rapidly than predicted⁷. Although only a small fraction of ice has melted recently, the Antarctic continent stores 90% of the world's ice, and the accelerated melting trend is cause for concern⁸.

There are a number of key threats to the integrity and survival of marine ecosystems as a result of climate change. Basic physical changes caused by global warming include more frequent storms, shifting ocean currents, melting polar ice, and rising sea levels. These physical changes threaten food supplies, species health, habitat, and reproduction. It remains unknown whether these impacts will be gradual or abrupt, but certain regions have already seen dramatic change. For example, rapid sea level rise is currently underway in the United States, China, and Argentina⁹, increasing flood risk in coastal areas. Temperature changes are also taking their toll: as water temperatures have risen, the base of the marine food chain in certain areas has crashed. And, one by one, the fish and birds farther up that food chain are crashing too¹⁰.

Temperature affects species in a number of ways: directly, by causing thermal stress, indirectly, by affecting food supply, and even more indirectly, by affecting the timing of seasonal events which in turn affect the ability of marine species to survive and reproduce.  Temperature also affects species by upsetting ecological balances, such as occurs with coral bleaching and subsequent mortality.  Warming of seawater also is predicted to impede the ability of shelled organisms to create calcium carbonate, which could doom coral reefs and impact entire marine food webs (see Ocean Observer on Ocean Acidification in the W2O archives).

Recent reports from the Mediterranean suggest that it is not only the extreme environments of the poles and tropics that are changing rapidly.  Warming of the Mediterranean Sea has resulted in a spread of invasive, thermophilic species (those species adapted to warmer waters), an overall loss of diversity, and the spread of marine disease. Continued climate-related degradation adds to a sea already stressed by development and resource use, and threatens one of the world's great natural treasures.

⁴Worm, B., H. K. Lotze, H. Hillebrand and U. Sommer. 2002.Consumer versus resource control of species diversity and ecosystem functioning. Nature 417

⁵Harvell, C.D., C.E. Mitchell, J.R. Ward, S. Altizer, A.P. Dobson, R.S. Ostfeld and M.D. Samuel. 2002. “Climate warming and disease risks for terrestrial and marine biota.” Science 296: 2158-2162. See also, Parson, E.A., L. Carter, P. Anderson, B. Wang and G. Weller. “Potential consequences of climate variability and change for Alaska.” U.S. National assessment of potential consequences of climate variability and change, Chapter 10. U.S. Global Change Research Program.

⁶Motavalli, Jim (ed.) 2004. Feeling the Heat: Dispatches from the Frontlines of Climate Change Routledge Publishers page 108.

⁷See Marc Kaufman’s Washington Post article entitled “Escalating Ice Loss Found in Antarctica – Sheets Melting in an Area Thought to be Unaffected by Global Warming. Page 1, January 14, 2008

⁸See article by Nicole Itano entitled “The Storied Mediterranean Faces Climate Change”, Christian Science Monitor Jan 14, 2008 edition

⁹Intergovernmental Panel on Climate Change. 2001. Third Assessment Report.

¹⁰Motavalli, Jim (ed.) Feeling the Heat page 119.