PASADENA, Calif., Sept. 21 (UPI) -- U.S. scientists say the Earth's average ocean surface temperature has declined since 2003, suggesting global warming trends aren't consistent.
Although the average upper ocean temperature has dropped since 2003, the decline is a fraction of the total ocean warming occurring during the previous 48 years, the researchers said.
"This research suggests global warming isn't always steady, but happens with occasional 'speed bumps'," said Josh Willis, a co-author of the study at the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena, Calif.
"This cooling is probably natural climate variability," Willis added. "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 change."
Willis said 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 so the recent cooling should have decreased sea levels during the past two years.
But levels have increased, suggesting sea level rise has shifted from being mostly caused by warming to being dominated by melting, Willis said.
The research appears in the journal Geophysical Research Letters.
