Some climate change skeptics have pointed out that global atmospheric temperatures have been stable, or even declined slightly, over the past decade. They claim it's a sign that global warming has either ceased, slowed down or is not caused by human activity. So, where did all that heat that we're supposedly producing go?
Climate scientists say it went into the ocean, which over the past 60 years has acted as a buffer against global warming. However, a new study led by Rutgers' Yair Rosenthal shows that the ocean is now absorbing heat 15 times faster than it has over the previous 10,000 years. Although the increased heat absorption by the ocean may give scientists and policymakers more time to deal with the issue of climate change, Rosenthal says the problem is real and must be addressed.
"We may have underestimated the efficiency of the oceans as a storehouse for heat and energy," Rosenthal said. "It may buy us some time – how much time, I don't really know – to come to terms with climate change. But it's not going to stop climate change."
Rosenthal, a professor of marine and coastal sciences in Rutgers' School of Environmental and Biological Sciences; Braddock Linsley of Columbia University's Lamont-Doherty Earth Observatory; and Delia W. Oppo of the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts, used the shells of tiny single-celled, bottom-dwelling foraminifera found in sediment cores to reconstruct the Pacific Ocean's heat content over the last 10,000 years. Their paper has been published in Science.
The heat content of the ocean had been measured before, but only instrumentally, and only back to the mid-20th century.
Their research was undertaken on marine sediment collected from the seas surrounding Indonesia, where the waters of the Pacific and Indian oceans overlap. The researchers measured the ratio of magnesium to calcium in the shells of a particular species of foraminifera, Hyalinea balthica. The warmer the waters when the organism calcified, the greater the magnesium to calcium ratio.
The shell chemistry of these tiny creatures provides a record of intermediate water temperatures going back 10,000 years, not only in the part of the Pacific where they were collected but from the higher latitudes in the Pacific as well. That's because the intermediate water in the western Pacific – depths between 450 and 1,000 meters – consists of water that once was near the surface in the northern and southern Pacific. The waters became saltier and colder over time and sank, then flowed very slowly toward the equator and through the passages between islands in Indonesia.
"Our work showed that intermediate waters in the Pacific had been cooling steadily from about 10,000 years ago" said Linsley. This places the recent warming of Pacific intermediate waters in temporal context. The trend has now reversed in a big way and the deep ocean is warming."