WASHINGTON (AP) -- The oceans have warmed significantly over the past four decades, providing new evidence that the Earth may be undergoing long-term climate change, a study by government scientists says.
The broad study of temperature data from the oceans shows average temperatures have increased from one-tenth to one-half degree, depending on depth since the 1950s, an amount described as surprising.The findings, reported Thursday by scientists at the National Oceanic and Atmospheric Administration, also may support the findings of computer climate models that suggest more severe temperature increases than are shown by actual historic surface temperature readings.
The computer models have produced temperature increases that are larger than those observed by surface and atmospheric monitors, prompting skeptics of global warming to say such modeling -- when used to predict future climate changes -- exaggerates the threat.
But the NOAA study has uncovered significant warming over the past 40 years in the oceans in depths of as much as 10,000 feet, suggesting this "missing heat" -- as one scientist characterized it -- may explain the difference between the computer simulations and actual readings.
"We've known the oceans could absorb heat, transport it to subsurface depths and isolate it from the atmosphere. Now we see evidence that this is happening," said Sydney Levitus, chief of NOAA's Ocean Climate Laboratory and principal author of the study.
Levitus and fellow scientists, who have worked on the project for seven years, examined temperature data from more than 5 million readings at various depths in the Pacific, Atlantic and Indian oceans, from 1948 to 1996.
They found the Pacific and Atlantic oceans have been warming since the mid-1950s, and the Indian Ocean since the early 1960s, according to the study published today in the journal Science.
The greatest warming occurred from the surface to a depth of about 900 feet, where the average heat content increased by 0.56 degrees Fahrenheit. Water as far down as 10,000 feet was found to have gained on average 0.11 degrees Fahrenheit.
"This is one of the surprising things. We've found half of the warming occurred below 1,000 feet," Levitus said in an interview. "It brings the climate debate to a new level. We can no longer ignore the ocean."
Jim Hansen, director of the National Aeronautics and Space Administration's Goddard Institute for Space Studies, said the expected warming of the Earth from so-called "greenhouse" gas emissions "would tend to give you a warming of the oceans of that magnitude."
"It confirms that the earth is heating up," said Hansen, who was among the earliest proponents of the argument that heat-trapping man-made pollution -- greenhouse gases, mainly carbon dioxide from burning fossil fuels -- in the atmosphere is causing global warming.
The study did not pinpoint the cause of the ocean warming trend over such a lengthy period, but said both natural and human-induced causes were likely.