ong-term deep ocean warming has been detected in the Indian, Pacific and Atlantic Oceans, as well as near both poles. Ocean warming, particularly in combination with coastal pollution, can promote the proliferation of toxic "red tides" and may encourage other diseases, such as cholera from bacteria that reside in plankton. Recent die-offs of manatees off the coast of Florida may have resulted from a toxic red tide enhanced by an oversupply of nutrients and warm sea surfaces.

Global warming may also be changing the patterns of the weather phenomenon called El Niño-a periodic climate event that occurs, on average, once every four years and is so strong that it has often been dubbed the "fifth season". The most recent El Niño phase-the most prolonged in recent history-caused the Pacific warm pool to persist for an incredible five years, causing myriad environmental impacts. El Niño shifted to the cold La Niña phase only recently, in August 1995. Both phases bring climate extremes to many regions around the globe. During the cold phase in 1995/96, many regions of the world experienced intense rains and flooding, following prolonged drought. Such rains have been associated with outbreaks of Murray Valley encephalitis and Ross River virus in Australia, and malaria in Argentina, southern Africa and Pakistan. No one yet knows whether the harsh recent El Niños indicate that global warming may cause this phenomenon to spiral out of control.