Now, however, a massive worldwide effort to sample Earth's ocean has found it has taken up about 30 percent of the CO2 generated by humans, and this represents only about one-third of the ocean's carbon-sink potential.

These measurements also nicely confirm the results achieved by climate modelers, and reinforce the accuracy of those models, as well as this aspect of their assessment of climate change.

So far, so good, but the large amounts of carbon being absorbed are damaging marine organisms, particularly corals and other invertebrate animals that form their shells via calcification.

For about 400,000 years prior to the industrial period, atmospheric CO2 fluctuated between 200 parts per million and 280 parts per million. Current concentrations are running about 380 parts per million, as a result of industrial and land-use activities of humans.

A paper published in the July 16 issue of the journal Science, authored by Christopher Sabine, an oceanographer with the National Oceanic and Atmospheric Administration, and colleagues, said that since 1800, fossil fuels burning and cement production have emitted about 244 petagrams -- about 270 billion tons -- of carbon into the atmosphere.

About two-thirds of these emissions have remained in the atmosphere, they wrote, increasing atmospheric CO2 concentration from about 281 ppm in 1800 to 359 ppm in 1994, which translates to an increase of (181.5 billion tons) of carbon.

When Sabine and colleagues conducted a number of calculations about the ocean's net carbon inventory and atmospheric changes from fossil fuel emissions, they arrived at a disturbing conclusion.

The ocean has constituted the only true net sink for anthropogenic (human-generated) CO2 over the past 200 years, they wrote. This means without the ocean absorbing CO2, atmospheric levels of the gas would be about 55 ppm higher today than what currently is being measured.

This is the first ocean data based on really solid evidence that we have as to how much carbon dioxide is being taken up by the ocean and how deep it is getting into the ocean, Jorge Sarmiento, professor of geosciences at Princeton University, told United Press International.

We've been estimating the oceanic uptake of carbon since the late 1950s, early 1960s, Sarmiento said. It was pretty rudimentary, but over time we've been improving our models. The answers have basically not changed. The uncertainties have narrowed, the models have become extraordinarily sophisticated.

Sarmiento agreed the results of the ocean carbon survey are a confirmation of the models.

This final database confirmation has no surprises in it, he said. It is reassuring that we really seem to have understood it very well. In contrast, our understanding of the land carbon sink -- I shouldn't call it understanding.

Collecting the data required a heroic effort consisting of 95 cruises looking at 9,618 hydrographic stations across the globe. Scientists were often at sea for months at time, in all conditions.

Even some skeptics are impressed.

The study by Sabine et al. certainly improves our knowledge of the absorption of human-produced carbon dioxide in the ocean, said Vincent Gray, a climate consultant in Wellington, New Zealand and author of The Greenhouse Delusion.

Gray told UPI he thought 9,618 hydrographic stations collected on 95 cruises is an impressive amount, but added that despite these impressive results, the papers do not seem to have added all that much to our knowledge of the carbon cycle.

He pointed to the carbon-cycle figures prepared by the Intergovernmental Panel on Climate Change, which gave no indication whatsoever of a trend, and therefore no means of forecasting the future. This paper helps just a little, but the future is still highly uncertain.

The future is always uncertain, of course, but the new data make a strong case for the ocean acting as a large potential reservoir for carbon.

Scientists estimate that because of ocean circulation and the current lack of evidence of carbon at depths greater than about 1 kilometer, the ocean has used up only about one-third of its potential as a carbon sink.

There is a huge body of untouched water in the deep ocean, Sarmiento said. The implications are that the oceans will continue to take up CO2.

This might be good news for humans and land animals, but it is definitely not encouraging for the ocean organisms that pull carbonate ions from sea water to produce shells -- corals, pteropod mollusks, foraminifera and coccolithophorids.

As CO2 increases in seawater, carbonate ion concentrations decrease. When they drop below a certain level, the shells of these creatures dissolve.

An accompanying paper in the July 16 Science, by NOAA oceanographer Richard Feely and others, estimated global calcium carbonate depletion rates and predicted "if carbon dioxide emissions continue to increase, ocean areas where shell dissolution occurs should expand. This trend would likely begin with colder, high latitude surface waters and proceed toward the equator."

Gray said, however: As for the speculation that all that carbon dioxide is weakening sea shells, this is hardly something new.� It has always been known that part of the carbon dioxide goes into the ocean, right back to the beginning of the greenhouse story.

The idea that marine organisms could be harmed by increased carbon levels� places little confidence on evolution, he said. Presumably some creatures will adapt to changed carbon dioxide more readily than others, as we are all doing right now on the land surface.

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