Pick a number between 1 and ...?

Climate-change chatter in the blogosphere over the Christmas holidays revolved around a provocative op-ed essay in the Washington Post by Bill McKibben, for whom 350 is the most important number. As in 350 parts per million of carbon dioxide in the atmosphere. It's a curious new strategy from one of the leading global warming activist types, and it bears exploring if for no other reason than it originates in the mind of none other than Jim Hansen.

Yes, that Jim Hansen, of NASA's Goddard Institute for Space Studies. Seems he gave an academic talk last month that got lost in the all attention paid to the new U.S. auto emission legislation and Al Gore, the IPCC and their Nobel award. Which is a shame, if McKibben is correct (and I can find no other reference for the talk other than pointers to McKibben's column).

"The safe upper limit for atmospheric CO2 is no more than 350 ppm," McKibben quotes Hansen saying. It's now 382 (more or less), so if we want to bring it down below current levels before all those nasty positive feedbacks start kicking in, there are going to have to be some changes made and pronto. McKibben writes that we should make that 350 ppm the primary goal, and organize the technological and social shifts required to forestall catastrophic climate change around that number.

Some are surprised by Hansen's target, saying it's way too ambitious. Joe Romm of Climate Progress prefers 450 ppm, writing that there's no way we can manage 350 in the time frame required, which is the next decade or so. Current practices will almost certainly result in reaching 550 sometime this century, raising temperatures 3°C or so and setting in motion all sorts of ecological events no one wants to see.

Of course, McKibben recognizes the challenge, describing the reality that

hides the biggest political and economic task we've ever faced: weaning ourselves from coal, gas and oil. The difference between 550 and 350 is that the weaning has to happen now, and everywhere. No more passing the buck. The gentle measures bandied about at Bali, themselves way too much for the Bush administration, don't come close...

Romm replies that

That would require replacing the world's entire energy infrastructure -- power plants, cars, planes, factories, fueling infrastructure, large parts of homes and commercial buildings -- while simultaneously deploying a hydrocarbon-free energy system in the rapidly-growing developing world....I say 450 needs a World War II scale effort starting in the next decade. I think 350 ppm is simply beyond serious practical and political consideration. You might as well tell people we need to develop a time machine to go back 20 years and warn the world that we need to start cutting emissions then ...

To McKibben's analogy of a new diet, Romm says people can change their diets overnight, but humanity cannot change its entire industrial base in less than several decades.

The fuss generated by this number is curious. It just represents another way of mathematically framing the question of what we should be doing. It is not news that Hansen thinks we need to slash our GHG emissions, and fast. For example, at about the same time he was pushing the 350 figure, he also suggested that any candidate for political office that is serious about the subject should, at the very least, call for a trio of measures including a moratorium on new coal plants in the Western World, a shutdown of existing (non-CO2-sequestering) coal plants in the west within 10 years, and a similar closure in the developing world within 20 years, and a consequential tax on carbon emissions.

So now, instead of debating whether that's feasible, we're quibbling over just how low CO2 levels needs to be. Up to now it was the shades of gray of fossil-fuel emissions reduction targets that defined the debate, including that of the various U.S. presidential contenders' climate change campaign planks: Clinton, Edwards, Obama, et al, say we should cut them by 80 percent by 2050. Richardson says 90 per cent. None are taking Hansen's anti-coal stewardship pledge, for fear of losing the votes of several coal-reliant states. So is talking instead about CO2 concentrations, a more science-oriented notion, but one that avoid demonizing specific industries, going to galvanize any more of the populace?

There are are metrics to consider. What about absolute quantities of emissions? As has been argued elsewhere, including on this blog, we could determine what the Earth can absorb ;;;;; 6 billion tonnes of annual CO2 (+ other greenhouse gas equivalent) emissions;;;;; and apportion that among the world's population, giving everyone about one tonne. Then come up with a schedule to bring current levels (> 20 tonnes person in the U.S., Canada and Australia) down to 1 tonne fast enough to avoid the danger zone (roundabout 2040).

The specific of that schedule will be the tricky bit, involving as it does the resolution of social, technological and political inequities between the rich and poor parts of the planet. For one thing, some very poor nations will actually be allowed to increase their paltry emissions because they are now below 1 tonne per citizen. How will that play in the U.S. Senate?

But will that be any harder than producing up with a plan to close all of America's coal plants? So-called "clean coal" plants inhabit a mythological future, what with more than a third of such prototypes being canceled recently thanks to "soaring construction costs, technology hurdles and uncertainty about regulation of greenhouse gases." (USA Today, Dec. 28)

So which target is best: CO2 concentrations, total emissions, per capita emissions or something else? Does it really matter which one? Matt Nisbet of Framing Science probably thinks it does, and he may be right. Or should we come up with a variety of complementary targets for various audiences? I suspect we probably need something specific that's shared by most of the planet. Wouldn't want to make it any more complicated than it currently is, after all.

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So which target is best: CO2 concentrations, total emissions, per capita emissions or something else? Does it really matter which one? Matt Nisbet of Framing Science probably thinks it does, and he may be right. Or should we come up with a variety of complementary targets for various audiences? I suspect we probably need something specific that's shared by most of the planet. Wouldn't want to make it any more complicated than it currently is, after all.

I think the answers will be hybrids of a one size fits all, and by geographic and other variations, a variety of complimentary solutions too.
Dave Briggs :~)