Humans have been pumping carbon dioxide into the atmosphere in ever increasing amounts since the industrial revolution began more than 200 years ago. It is a byproduct of the burning of carbon-based fossil fuels used in industry, automobiles, and for other purposes. This gas is believed to be contributing to global warming by surrounding Earth and trapping the Sun's radiation. But scientists report that this excessive carbon output might also be threatening ocean life.
The amount of carbon dioxide measured in the atmosphere is about 40 percent higher than 200 years ago. It has risen from 280 parts per million in 1800 to 380 parts today. Yet scientists calculate that human activity has generated much more carbon dioxide over that period than is observed in the atmopshere -- about twice as much.
Columbia University researcher Taro Takahashi says half of the human-induced CO2 emissions has been missing somewhere. "In other words, the effect of carbon dioxide warming has been halved due to unknown missing carbonm" he said
Now, the mystery of the missing carbon dioxide has been solved. Scientists report that it has been hiding in the world's oceans, transferred from the atmosphere, as some theorists had predicted. The leader of the study is U.S. government oceanographer Christopher Sabine.
"So we found over the 200 years that the oceans have taken up about 48 percent of all the fossil fuels, carbon that was released between 1800 and 1994," he said.
The findings are based on an exhaustive 10-year study by scientists from eight North American, European, and Asian nations who collected more than 72,000 sea water samples from all over the world and analyzed their chemical composition.
Mr. Sabine says just the carbon portion of the carbon dioxide emitted into the ocean over the last two centuries amounts to 118 billion metric tons. "A small car weighs about a metric ton, so we have released 118 billion small cars worth of carbon in the ocean, and this is just looking at carbon," he said.
In a second study, Mr. Sabine and colleagues report a potentially ominous conclusion from the carbon dioxide buildup. They say it has changed ocean chemistry in a way that might make it difficult for some marine organisms like coral, plankton, and tiny snails to form their shells. Excess carbon dioxide makes the ocean more acid. One of Mr. Sabine's co-researchers, California State University ocean biologist Victoria Fabry says laboratory experiments have shown that an increase in sea water acidity causes the shells to dissolve.
"So if these organisms in the field also show the same response that we see in the laboratory, then we could expect that CO2 would compromise the fitness or the success of those organisms. We might see that the structure of the food web would change and we might see shifts in the species compositions, but what the ultimate outcome would be we just don't have enough information to predict at this time," he said.
Christopher Sabine says the oceans are far from saturated with carbon dioxide and have the capacity to absorb a lot more to the potential detriment of the shell forming organisms. He points to some good news: Expanding areas of forests where farms once stood are soaking up more of the carbon. The bad news is that we humans continue to emit carbon pollution at faster and faster rates
"The CO2 has been increasing in the atmosphere at an exponential rate. Almost half of the CO2 emissions over the 200 year period have all been released in the last 20 years. This is growing dramatically, so the rate at which the oceans take up that CO2 will change proportionately."
Mr. Sabine's research appears in the journal "Science."