WASHINGTON (09/29/06) -- Average ocean water temperatures cooled slightly between 2003 and 2005 after a decade-long warming trend, according to a study recently released by the National Oceanic and Atmospheric Administration  (NOAA).

"This research suggests global warming isn’t always steady, but happens with occasional ‘speed bumps’," said study co-author Josh Willis of NASA’s Jet Propulsion Laboratory.

Researchers estimated the heat content of Earth’s ocean waters to a depth of about 760 meters, finding that this volume of water warmed by approximately 0.089 degree Celsius between 1993 and 2003. But from 2003 to 2005, the average temperatures fell by approximately 0.03 degree Celsius.

"This cooling is probably natural climate variability," said Willis. "The oceans today are still warmer than they were during the 1980s, and most scientists expect the oceans will eventually continue to warm in response to human-induced climate changes."

The heat content of the oceans reveals a great deal to scientists about the balance of energy for the planet as a whole.

"The capacity of Earth’s oceans to store the sun’s energy is more than 1,000 times that of Earth’s atmosphere," said John Lyman of NOAA’s Pacific Marine Environmental Laboratory in Seattle, Washington. "It's important to measure upper ocean temperature, since 84 percent of the heat absorbed by Earth since the mid-1950s has gone toward warming the ocean. Measuring ocean temperature is really measuring the progress of global warming."

Understanding this temperature fluctuation will allow scientists to develop better estimates of overall ocean temperatures -- a capability that will help design computer models to predict Earth’s climate.

The findings present the researchers with another puzzle about the relationship between ocean temperatures and sea-level changes. Cooler waters should suggest less melting of glaciers and ice sheets, melting that causes sea levels to inch up. But the data show the sea levels rose during the two-year period in which the cooler ocean temperatures were recorded.

This research is part of a far-reaching U.S. science and technology program to understand climate change and reduce emissions of greenhouse gases that are linked to this phenomenon. In 2006, the United States invested nearly $3 billion in technologies such as cold fusion, hydrogen fuel, and coal-powered, zero-emissions power generation.

The findings (PDF, 15 pages) are available online.

For additional information, see a climate change policy fact sheet on the State Department Web site.