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Oceanic findings confirm warming.

The world's oceans have warmed dramatically over the last four decades, according to research published in the March 24 issue of Nature. The new findings help resolve a disparity between the atmospheric temperature increases projected by climate models and those observed at the Earth's surface, adding credibility to the belief that much of the past century's warming has been human-induced. The discovery also guarantees that more atmospheric warming lies ahead, and suggests that the climate may be more sensitive to greenhouse gases than previously thought.

For years, climate modelers have been confronted with an apparent incongruity between the increases in temperature projected in their models and the relatively modest warming witnessed over the last several decades. The modelers have noted that oceans would absorb some of the heat trapped by greenhouse gases in the atmosphere, delaying but not stopping an eventual warming. But oceanographers have experienced difficulty in ascertaining whether this "missing warming" had indeed occurred in the ocean, having been hampered by patchy records of deep-ocean temperature.

To fill this research gap, a team of physical oceanographers from the National Oceanic and Atmospheric Administration (NOAA) engaged in a painstaking seven-year collection of millions of old deep-ocean temperature measurements made by hundreds of independent observers all over the world during the last 50 years. These neglected data had never before been compiled into a database; unlike meteorologists, oceanographers have not relied on a coordinated, global network for their observations. Pulled together, however, the rediscovered records enabled the scientists to construct "oceanic fever charts."

With some 5 million profiles of ocean temperature finally assembled, the NOAA scientists were able to identify a clear pattern: between 1955 and 1995, the world ocean--Pacific, Atlantic, and Indian basins--warmed by an average of .06 degrees Celsius from the surface to a depth of 3000 meters. This increase in thermal energy content is equal to nearly one-third of a watt per square meter, or the amount of energy used by 100 trillion 100-watt light bulbs over the course of a year. To the surprise of some scientists, half of the temperature increases were found in the upper regions, and half--more than previously believed--in the deepwater.

The ocean's rate of heat storage has major implications for climate change, as it is believed to be temporarily, but not indefinitely, slowing atmospheric warming. The NOAA researchers also note that increases in ocean temperature have preceded increases in atmospheric temperature by approximately a decade, implying that additional surface warming can be expected. James Hansen of NASA's Goddard Institute for Space Studies agrees, estimating that because of oceanic heat storage, surface temperatures would rise another 0.5 degrees Celsius over the next century even if greenhouse gas concentrations were stabilized immediately.

The ocean-induced delay of global warming is causing some scientists to believe climate may be more sensitive to rising greenhouse gas concentrations than widely thought. The "best estimate" of climate scientists had projected a 2-degree (C) increase in global temperature over the next century, but the new data has led some scientists to revise their projections upward, to a 3-degree increase or more.
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Author:Dunn, Seth
Publication:World Watch
Article Type:Brief Article
Geographic Code:1USA
Date:May 1, 2000
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