Revised theory suggests carbon dioxide levels already in danger zone

Yale University: If climate disasters are to be averted, atmospheric carbon dioxide (CO2) must be reduced below the levels that already exist today, according to a study published in Open Atmospheric Science Journal by a group of 10 scientists from the United States, the United Kingdom and France.

The authors, who include two Yale scientists, assert that to maintain a planet similar to that on which civilization developed, an optimum CO2 level would be less than 350 ppm — a dramatic change from most previous studies, which suggested a danger level for CO2 is likely to be 450 ppm or higher. Atmospheric CO2 is currently 385 parts per million (ppm) and is increasing by about 2 ppm each year from the burning of fossil fuels (coal, oil, and gas) and from the burning of forests.

“This work and other recent publications suggest that we have reached CO2 levels that compromise the stability of the polar ice sheets,” said author Mark Pagani, Yale professor of geology and geophysics. “How fast ice sheets and sea level will respond are still poorly understood, but given the potential size of the disaster, I think it’s best not to learn this lesson firsthand.”

…According to the study, coal is the largest source of atmospheric CO2 and the one that would be most practical to eliminate. Oil resources already may be about half depleted, depending upon the magnitude of undiscovered reserves, and it is still not practical to capture CO2 emerging from vehicle tailpipes, the way it can be with coal-burning facilities, note the scientists. Coal, on the other hand, has larger reserves, and the authors conclude that “the only realistic way to sharply curtail CO2 emissions is phase out coal use except where CO2 is captured and sequestered.”

…While they note the task of moving toward an era beyond fossil fuels is Herculean, the authors conclude that it is feasible when compared with the efforts that went into World War II and that “the greatest danger is continued ignorance and denial, which could make tragic consequences unavoidable.”…

This chart from Yale's website shows atmospheric CO2 if coal emissions are phased out linearly between 2010 and 2030, calculated using a version of the Bern carbon cycle model