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Carbon: 350.org

From the same people/studio who created the excellent video: The Story of Stuff.

350.org is an organization that is trying to let the entire planet's population know that atmospheric carbon dioxide needs to be stabilized at no more than 350 parts per million (ppm).

Source of tip: No Impact Man

1 Com:

Ben Courtice | June 28, 2008

The following comments were made by Phil Sutton, co-author of the book Climate Code Red, published in the next couple of days by Scribe.

The 350 target is better than a 450 target because it is 100 ppm less. But this target has no scientific relevance to our current problems and in my opinion should not be used or promoted as it misleads the public about what needs to be done.

The 350 target is being promoted by Bill McKibben and others because it was raised by Jim Hansen (and his coauthors) in April 2008 in a paper called "Target CO2: Where should humanity aim?" You can access this paper from:

Jim Hansen did give prominence to the 350 ppm figure but he called it an "initial target". This is how he presented it: "An initial CO2 target of 350 ppm, to be reassessed as effects on ice sheet mass balance are observed, is suggested."

But in the very next paragraph Hansen and coauthors say:

"*Stabilization of Arctic sea ice cover *requires, to first approximation, restoration of planetary energy balance. Climate models driven by known forcings yield a present planetary energy imbalance of +0.5-1 W/m2 [5], a result supported by observed increasing ocean heat content [76]. CO2 amount must be reduced to 325-355 ppm to increase outgoing flux 0.5-1 W/m2, if other forcings are unchanged. A further reduced flux, by ~0.5 W/m2,* and thus CO2 ~* *300-325* * ppm, may be needed to restore sea ice to its area of 25 years ago*.* Coral reefs are suffering from multiple stresses, with ocean acidification and ocean warming* principal among them [77]. Given additional warming ‘in-the-pipeline’, 385 ppm CO2 is already deleterious. *A * *300-350* * ppm CO2 target* would significantly relieve both of these stresses."

So where did the 350 initial target come from?

The authors of the "Target CO2: Where should humanity aim?" paper reviewed the paleoclimate data and concluded that the flip point for losing ALL the ice on the planet (including ALL of Antarctica) was probably somewhere in the range 425 ppm ± 75 pm. So somewhere between 500 ppm and 350 ppm we could lose ALL of the ice on the planet with the long run consequence of causing a sea rise of about 70 metres.

To have effectively a zero chance of causing such a catastrophe we would have to keep the CO2 level to below the bottom end of that range – ie below 350 ppm.

But the loss of all the ice on the planet is not the biggest short term worry. The total loss of the Arctic sea-ice in summer, the loss over the next few decades of all the ice in the Himalayas, the loss over 100 years of all the permafrost stored carbon, the acidification of the ocean, the overheating of the oceans, the loss of the Amazon rainforest, the loss of most of the Greenland ice sheet, the destabilisation and major loss of the West Antarctic ice sheet are all issues that have severe ramifications and require lower CO2 levels than 350 ppm.

The issue with the tightest requirements for recovery (that we know of so far) is the Arctic sea-ice. Hansen et al. suggests that to get that back, CO2 levels should be somewhere in the range 300 - 325 ppm. To be on the safe side we should keep the CO2 levels below the bottom edge of that range.

So if we are going to make a big issue out of an atmospheric CO2 level then using the paper by Hansen et al. we should go for *300 ppm* and NOT 350 ppm.

The 350 ppm target will not fully deliver a safe climate. I can see no merit in building up the 350 ppm figure up in the public mind as it will have to be replaced by a meaningful target in a short period of time. I've raised this issue with Bill McKibben and he has chosen not to respond. I've also raised it with Jim Hansen and he said that he had
been roundly condemned by some climate scientists for advocating a number that in their view was impossible to achieve. So his defence is not that the number is right scientifically but that it was a big jump to get from 550 or 450 ppm as a target to get down to 350 pm. But we don't need to worry about criticism based on pragmatism - we can go for the best scientific target based on the best science and using the Hansen et al. paper we can see already that that figure is most likely below 325 and could well be below 300 ppm.

Bear in mind that the scientific community has not modelled a safe climate future and so any figures we choose need to be taken with a degree of caution and that if we are to err we should err by going to the low end of any current estimates on the basis of the precautionary principle.

Also it is cucial that somewhere in the world that serious campaigners make sure they are not sucked into the ill-judged Bill McKibben campaign. We have something to offer the world by not falling in with his mistake.

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