Wednesday, October 13, 2004

Spike in greenhouse
gas a trend

Carbon dioxide levels read from
Mauna Loa continue a steady rise

HILO >> A recent sudden increase in the greenhouse gas carbon dioxide measured on Mauna Loa probably has little meaning for global warming, but the long-term trend is significant, two scientists say.

Charles Keeling of the University of California, San Diego, and Peter Tans of the National Oceanic and Atmospheric Administration were commenting on an upward blip of carbon dioxide recorded at NOAA's Mauna Loa Observatory in 2002 and 2003.

While the data don't show a runaway effect, in which greenhouse gases would grow dramatically, they do show five decades of increases.

"The carbon dioxide at Mauna Loa goes up every single year," Tans said. "It is 99.9 percent certain that it is due to us (human beings)."

Said Keeling: "There are several things that are happening to Earth's climate, which, when viewed together, are consistent with human-caused greenhouse warming, and probably not consistent with any other cause."

A British newspaper, the Guardian, reported earlier this week that the blip might be the beginning of runaway global warming. But Tans said yesterday that "I don't think it's such a big deal."

Keeling said the blip already ended and a normal rate of increase resumed this year.

He has been studying greenhouses gases on Mauna Loa since 1958, shortly after the observatory was established in 1956. The idea was that the observatory was so high, at 11,140 feet, and so far from cities, that gas measurements would be typical of worldwide concentrations.

When carbon dioxide measurements started, there were 315 parts per million molecules of air. The measurements grew for a while at a rate of about 0.7 parts per million per year. By about 1965, the average rate of increase was 1.5 parts per million. Except for a slight dip in the early 1990s, the average rate of increase grew to the present 1.75 parts per million a year, Tans said.

So when the amount jumped to 2.6 parts per million in 2002 and 2.1 parts per million in 2003, the increase was noteworthy, Tans said.

Using different instruments and methods, Keeling recorded 2.45 followed by 2.34 parts per million in the two years. The difference isn't significant, Keeling said.

He noted that measurements for nine months this year have fallen to 1.13 parts per million.

The 2002-03 blip was the second largest on record, Keeling said. Such peaks happen roughly every four years, with the highest reaching 3 parts per million in 1998, he said.

Tans said such blips normally start in the northern hemisphere and take about a year for the gases to spread into the southern hemisphere.

The scientists differed about the possible cause of the 2002-03 event, with Keeling suspecting a cause in nature and Tans seeing a possible cause in industrial growth in China and India.



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