The oceans have been steadily getting warmer over the past 50 years and could have a definite impact on the earth's overall climate, according to a study published Friday in Science magazine.
The first study on the long-term thermal changes in the planet's major oceans -- the Pacific, Atlantic and Indian -- shows that between 1948 and 1996 the temperature increased by an average of 0.06 degrees Celsius in the upper 300 meters (1,000 feet) of the world's oceans.
Researchers from the National Oceanic and Atmospheric Administrationsaid ocean temperatures remained fairly stable during the 1950s, increased during the 1970s, dropped off in the 1980s and increased to record levels in the 1990s.
"In each ocean basin substantial temperature changes are occurring at much deeper depths than we previously thought," NOAA administrator James Baker said in a comment accompanying the study.
The Pacific and Atlantic oceans began warming in the 1950s, while the Indian Ocean did so the following decade. By then, similar temperature increases in the Pacific and Indian oceans made it clear the same phenomenon was at work, the study said.
Scientists attributed the warming trend to a combination of natural causes and human activities, including the emission of greenhouse gases.
"It is possible that ocean heat content may be an early indicator of the warming of surface, air and sea surface temperatures more than a decade in advance," said the study's chief researcher Sydney Levitus, also with NOAA.