Has Climate Already Passed Dangerous Point?

Photo: James Hansen / Istock

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James Hansen, long an outspoken scientist warning of the dangers of doing nothing to stop global warming, has articulated a new position at odds with the scientific consensus stated by the United Nations' Intergovernmental Panel on Climate Change.

Rather than seeking to avoid a doubling of carbon in the atmosphere (compared to pre-industrial times) in order to avoid the worst consequences of global warming, Hansen suggests that the world has already passed this point. He says we've bought an ice-free world on carbon credit, and the climate will alter life as we know it unless we act to reduce the overall concentration of carbon in the atmosphere well below today's level.

"Paleoclimate evidence and ongoing global changes imply that today’s CO2, about 385 ppm, is already too high to maintain the climate to which humanity, wildlife, and the rest of the biosphere are adapted," he writes, with eight co-authors, in a draft paper that has not been accepted for publication. Policy makers had aimed to slow carbon emissions so that the concentration does not reach 450 parts per million, or ppm, double the pre-industrial concentration.

"Realization that we must reduce the current CO2 amount has a bright side: effects that had begun to seem inevitable, including impacts of ocean acidification, loss of fresh water supplies, and shifting of climatic zones, may be averted by the necessity of finding an energy course beyond fossil fuels sooner than would otherwise have occurred," Hansen writes. "We suggest an initial objective of reducing atmospheric CO2 to 350 ppm, with the target to be adjusted as scientific understanding and empirical evidence of climate effects accumulate."

As Andrew Revkin, the New York Times writer, points out in his Dot Earth blog, reducing emissions to the level Hansen suggests would be like rolling back the clock to 1988.

Accomplishing that would take tacking on a new tax or other cost for carbon, phasing out the use of coal, unless carbon emissions can be captured and stored (deep underground, most likely), and doing away with "unconventional" fossil fuels.

"The most difficult task, phase-out over the next 20-25 years of coal use that does not capture CO2, is herculean, yet feasible when compared with the efforts that went into World War II," Hansen writes. "The stakes, for all life on the planet, surpass those of any previous crisis. The greatest danger is continued ignorance and denial, which could make tragic consequences unavoidable."

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