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Oceans to acid

Oceans act as giant sponges for CO2 - but what eases global warming harms marine life.

By Peter N. SpottsStaff writer of The Christian Science Monitor / September 9, 2004

Call it the case of the missing "greenhouse gas." For years, scientists have been trying to figure out where carbon dioxide goes once humans generate it. Significant amounts billow into the atmosphere. But each year, atmospheric CO2 concentrations have been rising only half as fast as humans supply the gas.

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The hiding place, it turns out, is the world's oceans. And the implications for marine life are troubling, researchers say. If industrial CO2 emissions continue to increase at their current rate, by the end of the century the surface waters of the world's oceans are likely to become more acidic. Though the change appears subtle, it could threaten key organisms at the base of the marine food chain and further endanger shallow-water reefs, which represent some of the most biologically productive ecosystems on the planet. The absorption of this extra carbon dioxide would induce changes in ocean chemistry not seen for at least 20 million years, some researchers say.

"A lot has been said about carbon dioxide in the atmosphere" and its impact on climate, says John Raven, a marine biologist at the University of Dundee in Scotland. But geophysical chemistry also "has pretty firmly established that when CO2 in the atmosphere dissolves into the ocean, the surface ocean will become more acidic. That is something that is happening."

The oceans have been viewed as a potential brake on global warming through natural and engineered approaches to storing carbon- dioxide there. Ironically, it now seems that increased ocean uptake of CO2 "is not a good thing overall," he says.

One sign of growing concern over the issue comes from Britain, where the Royal Society - Britain's equivalent to the US National Academy of Sciences - late last month commissioned a six-month study to see what current research has to say about the ocean's carbon uptake and its effect on marine life. Prime Minister Tony Blair, who is slated to become president of the Group of Eight industrial countries next year, is said to have climate change high on his list of priorities for the next G-8 meeting. The Royal Academy study is expected to play a key role in those discussions.

The Royal Academy's announcement came a month after research results appeared in the US journal Science that solved the mystery of the missing CO2 and considered its biochemical consequences.

A research team, led by marine chemist Christopher Sabine, took on the herculean task of compiling a global picture of the oceans' CO2 uptake, based on measurements from some 70,000 samples of seawater. The samples were collected worldwide during two large oceanographic projects in the late 1980s and 1990s aimed at measuring ocean circulation and the movement of carbon through the system.

"We've known for years that the oceans take up a significant amount of carbon dioxide," says Dr. Sabine, with the Pacific Marine Environmental Laboratory in Seattle, part of the National Oceanic and Atmospheric Administration (NOAA). "But we haven't been able to quantify it based on direct measurements until now."

From 1800 to 1994, the team estimates, the oceans soaked up 48 percent of the carbon emitted from human activities, such as burning wood, coal, oil, or gas. Thus, the oceans are currently storing about a third of their long-term potential, the team concluded.

The real surprise, however, came from the impact the results had on the overall picture of the globe's carbon cycle,