Water makes up 70 percent of the Earth's surface, making it a very important set of ecosystems, including oceans, seas, wetlands, rivers, streams, and swamps. Climate change will affect all of these ecosystems in the form of increasing water temperatures, rising sea levels, or droughts brought on by rising air temperatures. (Refer to Chapter 7 for more about the natural disasters global warming may cause.) Exactly how these ecosystems will be affected, no one knows. Climate change is reshuffling the deck of water systems, and the world doesn't know what kind of hand it'll get dealt.
Many fish species are already at risk of extinction due to overfishing. According to scientists at Dalhousie University in Canada, fish populations have dropped more than 30 percent since the 1950s and are continuing to decrease. The projected loss from climate change will further elevate the risk of extinction.
Whether a few species are thriving or many species are declining in an ecosystem, these differences change the way the ecosystem functions. Each organism plays a role in an ecosystem. Ecosystems are remarkably adaptable; change the role of one organism, and the whole system alters in response. Global warming-related changes to ecosystems may cause some radical changes in their composition and how they function.
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