This is Scientific American's 60-second Science, I'm Julia Rosen.To us humans, climate change feels like something that’s happening to the atmosphere.But most of the action is actually at sea―about 90 percent of the heat that gets trapped by greenhouse gases is absorbed by the ocean.“So it’s really important to track that energy in the climate system and track the warming of the ocean.”Jorn Callies, an oceanographer at Caltech.Of course, the ocean is really big, and taking its temperature is hard.Satellites give information about the surface, and scientists have launched drifting devices that measure conditions in the upper mile of water.But researchers still struggle to collect data from the deep ocean, and to detect the long-term trends underlying day-to-day variations in temperature.Now, however, scientists have developed a new technique that allows them to measure temperature changes across entire ocean basins.The idea dates back to the 1970s, when researchers first proposed using sound waves to study ocean warming―because the speed of sound through water depends on the physical properties of that water, which are related to temperature.“And roughly, if we warm up the ocean temperature by one degree, the sound speed change―it would be four meters per second. And this is a very sensitive change.”Wenbo Wu, a seismologist also at Caltech, who led the study.That one degree he mentioned is a Celsius degree.
