2.1 Million-year high measured for carbon dioxide in atmosphere

Jun 18, 2009 - Jeremy van Loon - Bloomberg.com

June 18 (Bloomberg) -- Carbon dioxide in the earth’s atmosphere has risen to its highest level in at least 2.1 million years, according to a new investigation of the greenhouse gas’s role in ice ages over the millennia.

Researchers including Columbia University’s Baerbel Hoenisch drilled into the ocean floor off the coast of Africa to remove shells of ancient marine animals called foraminifera that contain climate records, according to the study published today on Science’s Web site. Previous evidence of CO2 concentrations found in columns of Arctic ice go back just 800,000 years.

Carbon dioxide, which traps heat close to earth, is the main contributor to global warming, threatening to raise sea levels and disrupt food production and water supplies, United Nations scientists have said. The marine sediment indicated “stable” levels of atmospheric CO2 at less than 250 molecules per million molecules of air, compared with about 385 today.

“What’s remarkable is how little CO2 concentration changed in the past,” said Jerry McManus, a paleoclimatology professor at Columbia who participated in the study. “What we’re seeing now is the same magnitude of natural variations happening in only a few decades.”

The CO2 concentration ranged between 181 and 297 parts per million over the period studied. It may be necessary to go back as far as 2.7 million years to find levels of CO2 similar to today’s, the study concluded, without attributing reasons for previous surges.

Carbon Spike

If the world continues to burn coal and oil and cut down forests that store carbon, the amount of CO2 in the atmosphere may more than double to 900 parts per million in the next century, the UN’s Environment Programme Executive Director Achim Steiner has said.

Negotiators at UN-sponsored talks are attempting to set limits on CO2 emissions. Delegates are focused on restricting output of the gas, which has grown 2 percent since industrialization in the 1800s, to 450 parts per million and slowing the rise in average global temperature to 2 degrees Celsius (3.6 Fahrenheit) over the next century.

“With unabated emissions, many trends in climate will likely accelerate, leading to an increasing risk of abrupt or irreversible climatic shifts,” 10 universities said today in a report suggesting that climate change was underestimated.

The United Nations Intergovernmental Panel on Climate Change in 2007 blamed global warming on emissions of such gases and warned of increased flooding and drought as temperatures continue to rise. Greenhouse gases also include water vapor, methane and nitrous oxide.

‘Unprecedented’

The study published in Science today “is the best existing record so far that shows atmospheric concentrations of carbon dioxide,” said Columbia’s McManus. “It strengthens the case that this is fairly unprecedented” for an increase in CO2.

Other evidence of greenhouse gas concentration has been discovered in ice. Polar researchers reported last year in the journal Nature that carbon dioxide was at an 800,000-year high, after studying bubbles trapped in ice drilled from the Antarctic.

Hoenisch and colleagues investigated the role of the carbon cycle in climate change and concluded that CO2 was probably not responsible for lengthening the time between major ice ages to 100,000 years from 40,000, countering a supposition that massive ice sheets grew and receded because of gradually decreasing levels of carbon dioxide.

Even with the likelihood of the earth warming up in the coming centuries, we’re headed for another ice age at some point thousands of years in the future, said McManus.

“The earth is moving into an increasingly glaciated state,” he said. “It’s just that the intervals between ice ages, which we’re living in now, have become longer and warmer.”

To contact the reporter on this story: Jeremy van Loon in Berlin at jvanloon@bloomberg.net.