Study finds all oceans are warming
MSNBC STAFF AND WIRE REPORTS
March 23, 2000
March 23 — U.S. government scientists on Thursday reported a significant — and surprising — warming of the world’s oceans over the past 40 years. The scientists said their findings provide evidence that computer models showing a global warming trend might be on target.
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 of up to 10,000 feet.
“In each ocean basin substantial temperature changes are occurring at much deeper depths than we previously thought,” James Baker, head of the National Oceanic and Atmospheric Administration, said in a statement. “This is just one more piece of the puzzle to understanding the variability of the earth’s climate system.
“Since the 1970s, temperatures at the earth’s surface have warmed, Arctic sea ice has decreased in thickness, and now we know that the average temperature of the world’s oceans has increased during this same time period.”
SUPPORT FOR MODELS
The findings might also 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 already has occurred, why should the model 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; the computer models do.
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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.
The oceans are one of the important, albeit barely understood, factors that determine climate. Owing to their large mass, the oceans can store heat for decades or longer. As a result, scientists hope someday they’ll be able to use ocean temperature measurements to forecast Earth’s climate decades in advance.
Sydney Levitus, who led the NOAA study appearing in Friday’s issue of Science, said it’s possible that the “ocean heat content” might be an “early indicator of the warming of surface, air and sea surface temperatures more than a decade in advance.”
“For example, we found that the increase in subsurface ocean temperatures preceded the observed warming of surface air and sea surface temperatures, which began in the 1970s.”
The study, the first to quantify temperature changes in all of the world’s oceans from surface to 3,000 yards deep, found that the most significant warming has occurred in the upper 300 yards, on average by 0.56 degrees F. The water in the upper 3,000 yards warmed on average by 0.11 degrees F.
“This is one of the surprising things. We’ve found half of the warming occurred below 1,000 feet,” Levitus said. “It brings the climate debate to a new level. We can no longer ignore the ocean.”
The scientists studied 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,
EL NINO DISCOUNTED
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 phenomena such as the El Niño effect as a significant factor. “We’re seeing a 35-year warming trend, and El Niño 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 dominant 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 NASA’s Goddard Institute for Space Studies.
Hansen is among the earliest proponents of the argument that heat-trapping human-caused pollution — greenhouse gases, mainly carbon dioxide from burning fossil fuels — is causing the earth to warm.
A U.N.-sponsored panel of more than 200 scientists has predicted that average global temperatures will increase 2 degrees to 6 degrees F 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 F over the past 100 years and that computer models used to predict future climate change are not reliable
The Associated Press contributed to this report.