THE global sea level this northern summer is 0.6 of a centimetre lower than last summer, NASA scientists say, in contrast to the gradual ocean rises of recent years.
The change stems from two strong weather cycles over the Pacific Ocean - El Nino and La Nina - which shifted rain patterns, scientists at NASA's Jet Propulsion Laboratory in Pasadena, California said. The two cycles brought heavy rains to Brazil and drought to the southern United States.
Researchers monitored the ocean's width, height, temperature and salinity through satellites and robot-operated floats, and presented their findings at the annual Gravity Recovery and Climate Experiment (GRACE) Science Team meeting in Austin, Texas, earlier this month.
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''This year the continents got an extra dose of rain, so much so that global sea levels actually fell over most of the last year,'' Carmen Boening, an oceanographer and climate scientist at the laboratory said.
Josh Willis, who also works at the lab, warned that this water would eventually return to the ocean, and the long-term trend of rising sea levels would continue.
''What this shows is the impact La Nina and El Nino can have on global rainfall,'' he said.
Computer climate models show sea levels are expected to rise because water expands as it warms, and the melting of glaciers and ice sheets in Greenland and Antarctica will contribute to global sea levels. The United Nations Intergovernmental Panel on Climate Change gave what it called a conservative estimate in 2007 that the ocean could rise between 18 and 147 centimetres by 2100. Recent research suggests it could rise by as much as 76 to 198 centimetres during this period.
The question of how much the ocean could rise due to warming is a topic of intense debate. In the past two decades global sea levels increased at a rate of roughly 0.3 centimetres a year, compared to 0.17 centimetres from 1961 to 2003, according to satellite data. A recent tide gauge study of sea levels in Australia and New Zealand, published in the Journal of Coastal Research, provided readings that suggested the rate of ocean rise has declined in the past decade.
Patrick Michaels, from the libertarian Cato Institute, noted that recent satellite data showed a slight decline in the rate of sea-level rise, which casts doubt on whether the ocean would expand as some predicted by the end of the century.
A US researcher who has been a target of climate-change sceptics has been cleared of wrongdoing by US investigators over the flap surrounding emails hacked from a British university.
The National Science Foundation found no "evidence of research misconduct" by Michael Mann, a professor of meteorology at Pennsylvania State University.
The foundation, based in Arlington, Virginia, closed its inquiry into Professor Mann, according to report from the inspector general for the agency, released last Monday.
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The university exonerated Professor Mann in February of suppressing or falsifying data, deleting emails and misusing privileged information.
Climate-change doubters pointed to the stolen emails, which surfaced in blogs in 2009, as proof that researchers conspired to quash studies questioning the link between human activity and warming.
Professor Mann was lead author of the first reconstruction of northern-hemisphere warming going back 1000 years, which showed recent temperatures increasing sharply. The 1998 findings have been confirmed by several studies, Professor Mann said.
"The way you get ahead in science is by proving the other guys wrong," Professor Mann said. "There is literally no study in the peer-reviewed scientific literature that contradicts our original conclusion."
Last week, Texas Governor Rick Perry, who is seeking the Republican nomination for president, renewed the assertion that scientists have "manipulated" data on climate change.
"It was a pretty definitive finding" that the charges "swirling around for over a year" were baseless, Professor Mann said in an interview.
"I was very pleased."
The report confirms findings from the US National Oceanic and Atmospheric Administration's inspector general and a separate panel of seven scientists based at universities in Britain, the US and Switzerland.
The University of East Anglia announced the committee. Ron Oxburgh, the former head of Shell Transport & Trading Plc and a member of the British House of Lords, was chairman.
'Closes the books'
"It certainly closes the books on Michael Mann and the emails," Joe Romm, a blogger for the Centre for American Progress, an advocacy group with ties to President Barack Obama's administration, said in an interview.
"They found nothing wrong with the science, or any evidence that there was anything wrong with how the scientists went about their work."
The inquiries focused on the University of East Anglia's climate-research unit, which stored the poached emails on its computer server.
The university's work contributed to some of the key findings of the United Nations Intergovernmental Panel on Climate Change, which has issued reports that blame human activity for rising temperatures.
Emails to and from Professor Mann were in the pilfered cache. One message by another scientist discussing Professor Mann's work spoke of a "trick" used in presenting data to smooth out year-to-year anomalies in climate-change information.
The National Oceanic and Atmospheric Administration's report, released in February, was requested by US Senator James Inhofe, an Oklahoma Republican who called the theory of man-made climate change a hoax. The report found no evidence of "manipulation of data".
"To say that the scientists have been vindicated is oversimplifying the situation," Matt Dempsey, a spokesman for Inhofe, said in an interview yesterday.
"What was revealed as part of the Climategate scandal was deeply troubling and certainly a setback for climate science."
A report on the dispute commissioned by the University of East Anglia found that, while the honesty and rigour of British scientists were not in doubt, they may have deleted emails to avoid having to make them public.
"There has been a consistent pattern of failing to display the proper degree of openness," the panel said in July 2010.
Climate change has emerged as an issue in the race for the Republican presidential nomination.
"There are a substantial number of scientists who have manipulated data so that they will have dollars rolling into their projects," Perry said last week. "I think we're seeing almost weekly, or even daily, scientists that are coming forward and questioning the original idea that man-made global warming is what is causing the climate to change."
Another Republican candidate, former Utah Governor Jon Huntsman, has said he believes human activity is causing climate change.