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The fact that everyone has to eventually eliminate their emissions and arrive at carbon neutrality makes it a little easier to construct an international policy framework. Achieving carbon neutrality is a grand challenge, but it's one that we can and must meet. The good news is that an international policy framework already exists. In the early 1990s, Aubrey Meyer, founder of the U.K.-based Global Commons Institute, developed "contraction and convergence." The concept is simple and straightforward.

First, you determine what level of global warming is tolerable and what is unacceptable. We'll use 2 degrees C as the threshold. Second, you determine the allowable emissions that would keep you within this target. Our analysis suggests 539 billion tonnes of carbon from 2001 onward (484 billion tonnes from 2007 onward). This corresponds to the assumption of a 4.5 degrees C climate sensitivity, the upper bound of the IPCC likely range, meaning that there is less than a 330/0 chance of breaking the 2 degrees C threshold. The final contraction target is carbon neutrality, and we'll assume this occurs in 2100.

Now we must allocate the 539 billion tonnes of carbon emissions to individual countries between 2001 and 2100. This is the convergence phase. On the convergence date, the principle of global equity is evoked, and every person on Earth is given the right to emit the same amount of carbon. That is, per capita carbon emissions for all countries converge to a common number. We'll use 2075 as the convergence year, although there is no reason why it could not be the same as the contraction year, 2100. Finally, a date has to be chosen beyond which additional credits are not gained for increasing your country's population. That is, increasing your allowable emissions by increasing your country's birth rate is not to be encouraged.
Keeping Our Cool
Professor Andrew Weaver

Review of Weaver's book here

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