But the global warming will continue

Sep 26, 2006 06:48 GMT  ·  By

A study realized by a team of National Oceanic and Atmospheric Administration (NOAA) show that average ocean water temperatures got down slightly between 2003 and 2005 after a decade of warming trend, despite the long term global warming trend.

The recent fall is about 20 % of the heat gained by the ocean between 1955 and 2003. "This research suggests global warming isn't always steady, but happens with occasional 'speed bumps'," said Josh Willis of NASA's Jet Propulsion Laboratory.

Earth's temperature has risen about 1 degree Fahrenheit (0.56 degrees Celsius) during the last century. Much of the warming in the past 50 years has been determined by the burning of fossil fuels and other man activities. "Average sea level goes up partly due to warming and thermal expansion of the oceans and partly due to runoff from melting glaciers and ice sheets," Willis said.

"The recent cooling episode suggests sea level should have actually decreased in the past two years. Despite this, sea level has continued to rise. This may mean that sea level rise has recently shifted from being mostly caused by warming to being dominated by melting. This idea is consistent with recent estimates of ice-mass loss in Antarctica and accelerating ice-mass loss on Greenland."

In parts of the Antarctic and Arctic, 84 percent of glaciers have retreated over the past 50 years. But the melting glaciers are not the reason for the cooling. "The amount of ice and water from the melting glaciers is very small compared to the overall temperature of the oceans," Willis told.

A small amount of cooling was detected at the ocean's surface by global measurements of sea-surface temperature. The top of the cooling was at a depth of 400 meters (about 1,300 feet), but substantial cooling was still observed at 2,500 feet, and the cooling appears to extend deeper.

The ocean waters at a depth of about 760 meters warmed by approximately 0.089 degree Celsius between 1993 and 2003 and fell by approximately 0.03 degree Celsius from 2003 to 2005. This area represents about 20 percent of the global ocean's average depth. "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 is important to predict 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.

"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."

"While global ocean temperatures have generally increased over the past 50 years, there have also been substantial decadal decreases."

"Other studies have shown that a similar rapid cooling took place from 1980 to 1983. But overall, the long-term trend is warming."

Understanding ocean's temperature fluctuation will help design computer models to predict Earth's climate. The heat stored by the ocean is important for determining the amount of total solar energy absorbed and reflected by the planet.