Human activity is having a measurable impact on one of the key triggers for global climate change -- the temperature of the world's oceans. That's the conclusion of a panel of U.S. researchers, presented at a recent meeting of the American Association for the Advancement of Science
Most scientists now believe that the Earth's climate is warming. "Approximately 90 percent of that warming has gone directly into the oceans," says marine physicist Tim Barnett. "So if you want to find out what is causing it, that's the place to look."
Mr. Barnett, a researcher with the Scripps Institution of Oceanography in San Diego, California, gathered evidence from computer models and field observations. The results of his study show rising ocean temperatures are directly related to human activity.
"Could the climate system simply do this on its own?" he asks. "The answer was clearly no. We looked at the possibility that solar changes and volcanic effects could cause the warming. Not a chance. What absolutely nailed it [confirmed it] was greenhouse warming. Two models, one from here and one from England, got the observed warming exactly (so much so that) we were stunned by the degree of similarity between the observations and the models."
Mr. Barnett says the new data paint a disturbing picture of global climate change. "The temperature driven impacts in things like regional water that these models predict in the next 20 or 30 years are severe," he says, "not only for the Western United States, but for places like China and Peru, anywhere that a temperature increase can cause a problem, anywhere that has a main water source that is fed by snow, anywhere that has a main water source fed by glacial melt as Western China does. Three hundred million people depend on that more or less for their summer water supply."
Ice melt - while occurring globally - is most apparent in the Arctic. Sea levels are rising because of it. Ruth Curry, with the Woods Hole Oceanographic Institute in Massachusetts, says an abundance of cold fresh water entering the northern North Atlantic could change the way the ocean transports heat from the low to the high latitudes.
"This has the potential to trigger other impacts in the climate system, beyond just the warming," she says. "As the earth warms, its water cycle is changing and in fact earth's water balance is being pushed out of kilter. These changes are happening now, and they are expected to amplify in the 21st century. And, it is a certainty that these changes will put serious strains on ecosystems and economies just about everywhere."
Rapid ice melting is already disrupting ecosystems that have evolved over long periods of time, according to Sharon Smith. She's co-director of the Oceans and Human Health Center at the University of Miami. She says a case in point is the recent die-off of hundreds of thousands of migratory birds called short-tailed shearwaters, which annually fly from Australia to the Arctic to breed. Five years of observations determined that warmer ocean conditions were to blame.
"It turned out that a very unusual plant [coccolithophore] bloomed in the Bering Sea in 1997," she says. "We all hypothesized initially that this (plant) couldn't be eaten by the lower levels of the food web that in turn supported the bird. It turned out that wasn't the case at all. The short-tailed shearwater is a visual predator, and this layer of coccolithophore on the surface of the ocean prevented the bird from seeing its prey underneath, and that is why they starved to death."
Sharon Smith, with the University of Miami's Oceans and Human Health Center, was one of a panel of scientists who presented their findings at a recent meeting of the American Association for the Advancement of Science here in Washington.