Humanity’s carbon budget

Eyes are on Bill McKibben’s Rolling Stone article, “Global Warming’s Terrifying New Math.”

The math is not really new, but that hardly seems to matter, for the terror is real — if you want to go there. McKibben has again written a defining piece.

The story in a nutshell goes like this. Forget peak oil. If the climate science we’ve come to call a “consensus” is anywhere close to correct, there are more than enough fossil fuels to fry the planet. Way more.

It’s the same story that George Monbiot wrote about earlier this month (“False Summit”), and in its essential outlines, it’s been known for years.

The key research was published in Nature in the spring of 2009. Two studies from the Potsdam Institute for Climate Impact Research estimated humanity’s carbon budget: the total amount of CO2 that we could emit and remain within the 2°C temperature increase most often considered a safe boundary. One study looked at carbon, the other CO2. They set different time horizons. Both studies counted metric tonnes (or “tonnes”), whereas I used “tons.” I reported the studies in “Totaling CO2 Emissions,” and a longer essay, “The Story of the Trillion Tons of Carbon.”

Of the trillion tonne budget, the Potsdam researchers found that, since the beginning of the industrial age, we’d already used up about half. Total emissions are continuously updated at trillionthtonne.org.

Catherine Brahic reported in an April 2009 New Scientist article (“Humanity’s carbon budget set at one trillion tonnes“) what has now become the Monbiot-McKibben story. When we know the total budget, any talk of fossil fuel constraints becomes, in climate terms, moot. We have too much, not too little. Fossil fuels need to stay in the ground.

I took a different approach. With an eye to the well-known divisions expected to manifest at the then-upcoming Copenhagen Climate Conference (COP15), I asked questions about climate justice: Who has benefited from the first half of the carbon budget and who gets to use the next half?

“We are in direct competition for a scarce resource with future generations,” said philosopher Henry Shue. “What portion of the remaining half trillion tons will be needed for global development to subsistence levels?”

In more fundamental terms: Now that we know what we know, how do we feel about it?

Bill McKibben’s piece deserves all the attention it’s getting. We live in challenging times, and the more people reflecting carefully on these issues the better.

But the math is not new. And — far more importantly — there are multiple ways to interpret what the calculations say.

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