Ocean warming in the last 30 years of the 20th century may have been significantly underestimated, new studies using satellite data and computer modeling suggest.
That's important because of the impact of the oceans on the world's climate systems, experts say, with about 90 percent of global warming's heat going into the world's seas.
"When we think about global warming, what we should really thinking about, to be honest, is ocean warming," says oceanographer and climate modeler Paul Durack of the Lawrence Livermore National Laboratory in California.
Durack was lead author on one of two studies recently published in the journal Nature Climate Change.
"By using satellite data, along with a large suite of climate model simulations, our results suggest that global ocean warming has been underestimated by 24 to 58 percent," he says.
He put the underestimation down to poor sampling in the period 1970 to 2004 and to methods of analysis for data-sparse regions that led to conservative estimates of temperature changes.
That changed by 2004 as scientists completed a network of 3,000 floating sensors, spread around the world in a system dubbed ARGO.
Using ARGO, researchers could gather information on ocean temperatures down to depths of 6,500 feet, far deeper than any previous technology could offer.
"The conclusion that warming has been underestimated agrees with previous studies, however it's the first time that scientists have tried to estimate how much heat we've missed," Durack says.
In the Southern Hemisphere's oceans in particular, Durack and his colleagues report, warming has occurred at a much higher rate during the past decades than previously thought, the researchers said.
In another study, published in the same journal issue, it was determined the deepest layers of the oceans -- below the 6,500-foot level -- have warmed very little over the last decade.
That suggests much of the impact of recent global warming is being experienced close to the ocean surface, says co-author Joshua Willis at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The availability of increasingly accurate measurements of ocean temperatures has allowed scientists to re-examine historical and current trends in ocean warming, he says.
"We are getting better equipment, better instruments, more of them," Willis says. "Both of these studies are looking at how [ocean temperature] is changing over time. And the more we can learn about what happened in the past, the better we'll be able to predict what is going to happen in the future."
