Global Environment Outlook 3 (GEO 3)

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COASTAL AND MARINE AREAS

Part of the fishing industry’s inadvertent by- catch — a seal ensnared in broken fishing net Source: UNEP, L. K. Nakasawa, Topham Picturepoint

Global climate and atmospheric change The rapid global warming caused by human-induced changes in the atmosphere that is projected by the IPCC would have dramatic effects on the ocean (IPCC 2001), threatening valuable coastal ecosystems and the economic sectors that depend upon them. Other potential impacts are complex and poorly understood. Polar warming, and melting of the ice caps, could slow down the global atmosphere/ocean ‘heat engine’, potentially altering the flow of major ocean currents (Broecker 1997). The warming of the ocean’s surface layers, and an increased input of fresh water, could reduce the upwelling of nutrients that supports much of the ocean’s productivity. On the other hand, the highly productive upwelling on the eastern side of some oceans could intensify if, as some projections predict, relatively greater warming occurs there (Bakun 1996). The IPCC predicts that storms and other extreme weather events will increase in frequency and intensity (IPCC 2001), increasing natural disturbances to coastal ecosystems and perhaps reducing their ability to recover.

There is particular concern about the possible effects of global warming on coral reefs. During the intense El Niño of 1997-98, extensive coral bleaching occurred on coral reefs worldwide (Wilkinson 1998, Wilkinson and others 1999). While some reefs quickly recovered, others, particularly in the Indian Ocean, Southeast Asia and the far western Pacific, suffered significant mortality, in some cases more than 90 per cent (Wilkinson 1998, 2000). Some models predict a long-term shift to an increased frequency and intensity of El Niño events or similar conditions. If this occurs, bleaching could also become more frequent and intense, with irreversible damage to reefs. There is evidence that a long-term decline of reefs in the remote Chagos archipelago in the Indian Ocean is related both to El Niño events and to a long-term rise in surface temperature (Sheppard 1999). Mass bleaching of reefs in various parts of the world was also observed in 2000, a possible sign that bleaching is becoming more frequent. Reefs may also be threatened by a higher concentration of CO 2 in seawater which impairs the deposition of their limestone skeletons.