But researchers at the Scripps Institution of Oceanography believe they can get a much better picture of possible global warming if they look at the weather in the water.
"Is the ocean warming up, for example? In some ways, that would be a much more convincing measure than what's happening in the atmosphere," said Peter Worcester of the institute.
But determining that has been problematic. Satellites see only the surface - not changes happening below.
So Peter Worcester and his colleagues devised an ingenious method to monitor ocean temperatures using the principle that sound travels faster in warmer water than it does in cold.
"We can make very accurate measurements of ocean temperature over these vast areas of ocean," Worcester said.
They've droppped huge arrays of sound sensors in the Pacific Ocean and tied into the Navy's underwater system to detect enemy submarines. By measuring the difference in time it takes generated sounds to reach the sensors, they can create incredibly detailed weather maps of the ocean from surface to bottom.
"If ocean temperatures start to change as a result of global warming, I think you can see the kinds of effects on storm frequency, precipitation, seasonal changes that we see from El Nino," Worcester said.
It's too early to tell if the oceans are warming, but from these first experiments, scientists now believe if it is, they'll know about it.
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