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Thank You, El Nino

Do you remember all the rain, the flooding, and the mudslides out in California Last year?

There still might be a silver lining at that, reports CBS This Morning Meteorologist Craig Allen.

A study by the National Oceanic and Atmospheric Administration found that from 1991 to 1994 - years when El Nino warmed the Pacific - the ocean released 30 percent to 80 percent less carbon dioxide, a gas that is believed to trap heat in the atmosphere.

The finding was published in Thursday's issue of the journal Nature.

Scientists commonly estimate how much carbon dioxide should be in the atmosphere by calculating how much fossil fuel is burned. But 2 billion tons of carbon dioxide go unaccounted for each year.

According to the NOAA research, reduced carbon dioxide releases in the Pacific during El Nino could account for about 16 percent to 36 percent of this "missing" CO2.

"Obviously, we are very, very interested in where the CO2, which we are releasing every year during fossil-fuel burning, ends up," said Rik Wanninkhof, an NOAA oceanographer.

Understanding the year-to-year changes in CO2 levels is key to explaining how the oceans, the land and the atmosphere regulate Earth's climate.

Carbon dioxide levels in the atmosphere have been rising for decades, a phenomenon blamed on increased burning of fossil fuels and deforestation. Some scientists say this has contributed to this century's global warming trend.

Previously, episodes of El Nino, the naturally occurring, cyclical warming of the Pacific blamed for causing uproars in weather patterns, were shown to spur more plant growth, which in turn sucks carbon dioxide out of the atmosphere. The NOAA research shows yet another way El Nino helps reduce CO2 levels.

Usually, the equatorial waters of the Pacific are the source of three-quarters of the carbon dioxide released by the world's tropical oceans. The northern Pacific sucks up all of that carbon and more each year, making it one of the biggest "carbon sinks," or areas that absorb carbon dioxide.

El Nino intensifies that process: The trade winds along the equator die down, so the upwelling of cold, carbon-rich waters decreases and less CO2 is sent into the atmosphere.

According to the NOAA study, the equatorial Pacific released 900 million tons of carbon in 1996, a normal year. The same seas released 300 million tons in 1992, 600 million tons in 1993 and 700 million tons in 1994.

Scott Doney, an oceanographer with the National Center for Atmospheric Research, said what is different about this study is the wealth of data the researchers were able to gather. The scientists put their equipment on NOAA ships servicing 80 weather stations all over the Pacific.

"They've got good snapshots for six or seven different areas through a pretty major period," he said. "This study is very important in terms of diagnosing what happend to the carbon dioxide."

There may be an irony there, reports Allen. The level of greenhouse gases appears to affect El Nino and it may turn out that they cancel each other out.

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