In a reconstruction of Pacific Ocean temperatures in the last 10,000 years, researchers have found that its middle depths have warmed 15 times faster in the last 60 years than they did during apparent natural warming cycles in the previous 10,000.
Study co-author Braddock Linsley, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory,s adi that they're experimenting by putting all this heat in the ocean without quite knowing how it's going to come back out and affect climate.
He said that it's not so much the magnitude of the change, but the rate of change.
Ocean heat is typically measured from buoys dispersed throughout the ocean, and with instruments lowered from ships, with reliable records at least in some places going back to the 1960s.
To look back farther in time, scientists have developed ways to analyze the chemistry of ancient marine life to reconstruct the climates in which they lived. In a 2003 expedition to Indonesia, the researchers collected cores of sediment from the seas where water from the Pacific flows into the Indian Ocean.
By measuring the levels of magnesium to calcium in the shells of Hyalinea balthica, a one-celled organism buried in those sediments, the researchers estimated the temperature of the middle-depth waters where H. Balthica lived, from about 1,500 to 3,000 feet down.
The temperature record there reflects middle-depth temperatures throughout the western Pacific, the researchers say, since the waters around Indonesia originate from the mid-depths of the North and South Pacific.
Over the last 60 years, water column temperatures, averaged from the surface to 2,200 feet, increased 0.18 degrees C, or .32 degrees F.
Linsley said that might seem small in the scheme of things, but it's a rate of warming 15 times faster than at any period in the last 10,000 years.
The study has been published in the journal Science.