An team of 10 researchers — including Yale professors of geology and geophysics Mark Pagani and Robert Berner — determined that current levels of carbon dioxide have already surpassed the estimated cutoff level that would cause damage to the planet. The study also found that this threshold level is actually much lower than previously estimated. Still, one Yale climate expert said it would be impossible to implement policies to reach the goal the study sets out.

Past research on greenhouse gases indicated that 450 parts per million of atmospheric CO2 would be the “tipping point” beyond which the effects of global warming would begin to rapidly escalate. But the study, which was headed by James Hansen, a professor of Earth and Environmental Studies at Columbia University and NASA’s lead climate scientist, revised this theory, showing that this threshold level is closer to 350 ppm. The level of CO2 found in the atmosphere — 385 ppm — is already higher than this, and is increasing annually by two ppm.

“It appears as if we have reached CO2 levels not seen for the past several million years,” Pagani said in an e-mail to the News.

The study concluded that avoiding climate disasters depends on reducing our reliance on fossil fuel.

An escalation in climate changes that are already occurring — including heavy rainfall and floods, more intense dry periods and fires, and shifting of climatic zones — will eventually bring about irreversible changes, such as extermination of species and sea level rise as a result of ice sheet disintegration, Hansen said.

President-elect Barack Obama’s transition team has said it plans to implement an economic cap-and-trade plan that would reduce emissions of greenhouse gases and invest into renewable energy sources.

According to the study, coal burning is the greatest source of atmospheric carbon dioxide and its use needs to be phased out altogether. Twenty-five percent of CO2 emissions from fossil fuels linger in the air for several centuries, Pagani noted.

The authors cited several recommendations for reducing CO2 levels, including improving agricultural practices and reforestation. Geo-engineering methods, such as artificial removal of CO2 from the atmosphere, were discounted as too expensive.

Hansen said that re-attaining climatic conditions similar to those of the pre-industrial period can only be achieved if the carbon contained in our remaining fossil fuel reserves is never emitted into the atmosphere.

But Arnulf Grubler, professor of energy and at the Yale School of Forestry and Environmental Sciences, said that the study does not make any practical suggestions for achieving such a low level of atmospheric CO2 in such a short period of time.

Grubler also said that the study did not take into account the other factors that must be addressed before any plan for reducing CO2 levels can be implemented. The study also betrayed a lack of awareness about policy making, Grubler added.

The study was published in the 2008 edition of the Open Atmospheric Journal.

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