Evidence of global warming's effects on aquatic environments is already abundant. In California, scientists have documented a 4 degree Fahrenheit rise in water temperatures in Monterey Bay that coincides with a massive northward shift of entire populations of sea life. In Alaska, the decline of pollock and other fish populations has been linked to warming temperatures, as have erratic shifts in salmon runs. Warming ocean temperatures around Antarctica have shrunk ice cover and caused major damage to populations of krill, a small shrimp-like crustacean. Krill is the base of the food chain in Antarctica and is vital to the survival of penguins and whales, as well as numerous fish and sea birds.
Coral bleaching due to global warming is the most serious threat to coral reefs.
Rising water temperatures heat the coral, breaking down the complex biological system that coral have evolved to survive. In some places, water temperatures are nearing the coral's heat tolerance.