Thursday, April 30, 2009

Know Your Limit - A Trillion Tonnes. Global Warming Gets New Metrics.

Climate scientists have come up with a new approach to measuring anthropogenic (man-made) global warming. They've worked out the maximum quantity of carbon dioxide we can cram into our atmosphere if we have any hope of staying within the 2-degree celsius target. It's a trillion tonnes.

Now that's not another trillion tonnes, but a trillion tonnes all in. A second study just released puts the ceiling at 0.9 trillion tonnes. From the Environmental News Network:

Rather than basing negotiations on short-term goals such as emission rates by a given year, the researchers say the atmosphere can be regarded as a tank of finite size which we must not overfill if we want to avoid a dangerous temperature rise.

Climate policy has traditionally concentrated on cutting emission rates by a given year, such as 2020 or 2050, without placing these goals within the overall context of needing to limit cumulative emissions.

...The first study, led by Myles Allen from the University of Oxford, UK, found that releasing a total of one trillion tonnes of carbon dioxide into the atmosphere between 1750 and 2500 would cause a "most likely" peak warming of two degrees Celsius. Emissions to 2008 have already released half of this.

Allen said in a press briefing this week (27 April): "It took 250 years to burn the first half trillion tonnes and, on current predictions, we'll burn the next half trillion in less than 40 years."

David Frame, a co-author of the Allen paper and researcher at the University of Oxford, said that these findings make the problem "simpler" than it's often portrayed.

"[The findings] treat these emissions ... as an exhaustible resource. For economists, this way of looking at the problem will be a huge simplification," Frame said.

"Basically, if you burn a tonne of carbon today, then you can't burn it tomorrow've got a finite stock. It's like a tank that's emptying far too fast for comfort. If country A burns it, country B can't. It forces everyone to consider the problem as a whole."

What's not mentioned directly in the article is the enormously powerful significance of a global ceiling on carbon emissions - rationing. It makes possible arguments we haven't heard much of before. For example, we've got around 6.7-billion people today. If we allocate the remaining half-trillion tonnes on a per capita formula it would be disastrous for the industrialized nations. Even under an international cap and trade system, carbon quotas could become enormously expensive. It brings to mind the situation in California where farmers with water quotas choose to simply sell their quotas to desperate municipalities and give up farming altogether.

I expect these studies could be right. After all, there has to be some limit to the atmospheric emissions the earth can sustain. Everybody pretty much already knows that. But to put a number on it gives the debate an entirely new dimension, a clear yardstick against which each nation can be measured and, in seeking co-operation, clarity could be toxic.

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