Oceans may be absorbing Earth's warming, study suggests

Oceans may be absorbing Earth's warming, study suggests

By H. JOSEF HEBERT, Associated Press

WASHINGTON (March 23, 2000 6:40 p.m. EST http://www.nandotimes.com) - Scientists have discovered a significant warming of the world's oceans over the past 40 years, providing new evidence that computer models may be on target when they predict the Earth's warming.

The broad study of temperature data from the oceans, dating to the 1950s, shows 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 down to 10,000 feet.

The findings, reported by scientists at the National Oceanic and Atmospheric Administration, also 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 the computer models have exaggerated warming that already has occurred and should not be be trusted to predict future warming.

The historical data, for the most part, is based primarily on surface and atmospheric readings and does not take into account heat trapped in the oceans, as the computer models do.

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. 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 in the journal Science on Friday.

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."

The study did not pinpoint the cause of the warming trend over such a lengthy period, but said both natural and human-induced causes were likely.

Levitus discounted short-term climate phenomenon such as the El Nino effect as a significant factor.

"We're seeing a 35-year warming trend and El Nino occurs on a time scale of two to seven years. 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 major breakthrough.

"It confirms that the earth is heating up. ... It confirms that the dominate climate forcing has been greenhouse gases which would tend to give you a warming of the oceans of that magnitude," said Jim Hansen, director of the National Aeronautics and Space Administration's Goddard Institute for Space Studies.

Hansen is among the earliest proponents of the argument that heat-trapping manmade pollution - greenhouse gases, mainly carbon dioxide from burning fossil fuels - is causing the Earth's warming.

A U.N.-sponsored panel of more than 200 scientists has predicted that average global temperatures will increase 2 degrees to 6 degrees Fahrenheit by the end of the century if current greenhouse gas emissions are not curtailed.

Such warming is believed by many scientists to have broad economic and environmental impact including sea level rise as well as changes in agriculture and human health.

Critics of these predictions believe that global mean temperatures have increased only about 1 degree Fahrenheit over the past 100 years and that computer models used to predict future climate change are not reliable.

While the oceans overall still are becoming warmer, there is evidence that parts of the deep waters of the North Atlantic have begun to cool. "Which leaves the question, where is the heat going," Levitus said.

Likely, it is going to the surface, If so, Levitus suggested the warmer ocean temperatures "may be an early indicator of the warming of surface, air and sea surface temperatures" a decade from now.