
Hot coals: If you burn a tonne of carbon today, you can't burn it tomorrow
Flickr/Adam Pilarski
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Scientists hope a new approach to assessing carbon build-up in the atmosphere will simplify issues for policymakers and economists.
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Two papers published in Nature today (29 April) show that the timings of carbon emissions are not relevant to the debate — it is the total amount of carbon dioxide emitted over hundreds of years that is the key issue.
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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.
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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.
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Both papers analyse how the world can keep the rise in average surface temperatures down to no more than two degrees Celsius above pre-industrial levels.
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This figure is widely regarded as the threshold beyond which the risk of dangerous climate change rapidly increases. Policymakers around the world have adopted this limit as a goal.
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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.
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Emissions to 2008 have already released half of this.
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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."
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The second study, led by Malte Meinshausen at the Potsdam Institute for Climate Impacts Research, Germany, used a computer model to demonstrate that to avoid exceeding two degrees Celsius by 2100, cumulative carbon emissions must not exceed 0.9 trillion tonnes.
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"We have already emitted a third of a trillion in just the past nine years," Meinshausen says.
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.
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"[The findings] treat these emissions ... as an exhaustible resource.
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For economists, this way of looking at the problem will be a huge simplification," Frame said.
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"Basically, if you burn a tonne of carbon today, then you can't burn it tomorrow … you've got a finite stock.
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It's like a tank that's emptying far too fast for comfort.
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If country A burns it, country B can't.
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It forces everyone to consider the problem as a whole."
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In a separate essay, Stephen Schneider of the Woods Institute for the Environment at Stanford University in the United States, discusses what a world with 1,000 parts per million of carbon dioxide in its atmosphere might look like.
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Link to full Allen et all paper in Nature.
Link to full Meinshausen et al paper in Nature.
Link to essay in Nature.
Naomi Antony
SciDev