Oceans have warmed in last 40 years, study finds
The research gives credence to computer models that predict a rise in the planet's temperature.
By H. Josef Hebert
WASHINGTON - Scientists have discovered a significant, even surprising, warming of the world's oceans over the last 40 years, providing new evidence that computer models may be on target when they predict Earth's warming.
The broad study of temperature data from the oceans, dating to the 1950s, shows that average temperatures have increased more than expected - about half a degree Fahrenheit closer to the surface, and one-tenth of a degree even at depths of up to 10,000 feet.
The findings, reported by scientists at the National Oceanic and Atmospheric Administration, may explain a major puzzle in the global-warming debate: why computer models have shown more significant warming than actual temperature data.
Global-warming skeptics contend that if the computer models exaggerate warming that has already occurred, they should not be trusted to predict future warming. The models have shown higher temperatures than those found in surface and atmospheric readings. But now, the new ocean data may explain the difference, scientists said.
In the NOAA study, scientists for the first time have quantified temperature changes in the world's three major ocean basins and at such depths.
"We've known the oceans could absorb heat, transport it to subsurface depths, and isolate it from the atmosphere," said Sydney Levitus, chief of the NOAA's Ocean Climate Laboratory and principal author of the study. "Now we see evidence that this is happening."
Levitus and fellow scientists, who have worked on the project for seven years, examined temperature data from more than five million readings at various depths in the Pacific, Atlantic and Indian Oceans from 1948 to 1996. They found that the Pacific and Atlantic 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.
The study did not pinpoint the cause of the warming over such a lengthy period but said both natural and human causes were likely.
Levitus discounted short-term climate phenomena such as the El Nino effect as major factors.
"There's something much more significant occurring than just short-term variability," he said.
Other scientists who have argued that the ocean has masked actual global temperature increases called the findings a breakthrough.
"It confirms that the Earth is heating up," said Jim Hansen, director of NASA's Goddard Institute for Space Studies.
A U.N.-sponsored panel of more than 200 scientists has predicted that average global temperatures will increase 2 to 6 degrees Fahrenheit by century's end if greenhouse gas emissions are not curtailed.