Report: At 385 PPM, Current CO2 Level Already in “Dangerous Zone”

What’s the optimum level of atmospheric CO2 for humanity and nature? It’s less than the amount in the air today and must be taken back:

If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that.

-- Dr. James Hansen et al, "Target Atmospheric CO2: Where Should Humanity Aim?"
The Open Atmospheric Science Journal, November 2008

The whole report is here. It’s worth a read. Its authors -- NASA climate scientist James Hansen and nine other scientists from the US, UK and France -- make the scientific case that most of the remaining fossil fuel carbon on the planet must never be emitted to the atmosphere, if we are to preserve a climate to which humanity is accustomed.

The most important implication of their findings is that all coal use -- except where CO2 is captured -- must end by 2030.

The reason for the urgency is that the present level of CO2 in the atmosphere -- 385 parts per million (ppm) -- is "already in the dangerous zone," say the researchers. Indeed, it’s "already deleterious." It’s "already a major threat." And it’s increasing 2 ppm each year.

The report suggests that the global initial target for atmospheric CO2 should be 350 ppm, although it’s likely to be lower once more studies are completed. Interestingly, that finding -- that humanity must aim for a CO2 amount less than the current amount -- represents a dramatic change. Most climate analyses to date have settled on a concentration of 450 ppm as being capable of thwarting catastrophic climate change. But Hansen et al now realize from improved data on the Earth’s climate history and from their ongoing observations of change that:

A CO2 amount of order 450 ppm or larger, if long maintained, would push Earth toward the ice-free state. Although ocean and ice sheet inertia limit the rate of climate change, such a CO2 level likely would cause the passing of climate tipping points and initiate dynamic responses that could be out of humanity’s control.

What about today? The report finds that climate impacts are in fact already occurring:

Alpine glaciers are in near-global retreat. After a one-time added flush of fresh water, glacier demise will yield summers and autumns of frequently dry rivers, including rivers originating in the Himalayas, Andes and Rocky Mountains that now supply water to hundreds of millions of people. Present glacier retreat, and warming in the pipeline, indicate that 385 ppm CO2 is already a threat.

In sum, here are the report's main conclusions, my italics:

• It is conceivable to reduce CO2 to less than the current amount of 385 ppm.
• The only realistic way is through a total phase out of coal in the next 20 to 25 years, except where CO2 is captured. (Other policy musts include a rising global price on CO2 emissions and a reward system for improved agricultural and forestry practices that sequester carbon.)
• The task is "Herculean yet feasible when compared with the efforts that went into
  World War II."
• "The greatest danger is continued ignorance and denial."

Now, the threat of climate inaction and denial to humanity and future generations is indisputable. But knocking out coal altogether in two and a half decades? The moral imperative is clear. But politically "realistic" and "feasible?"

Thoughts?

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