How big an effect on world temperature will Australia's proposed carbon tax have?

Lord Monckton has been kind enough to give me the straight answer that Flannery et al will not - and his answer explains exactly Flannery's embarrassed silence:

Q. What is the central estimate of the anthropogenic global warming, in Celsius degrees, that would be forestalled by 2020 if a) Australia alone and b) the whole world cut carbon emissions stepwise until by 2020 they were 5% below today's emissions?

Answer a). Australia accounts for (at most) 1.5% of global carbon emissions. A stepwise 5% cut by 2020 is an average 2.5% cut from now till then. CO2 concentration by 2020, taking the IPCC's A2 scenario, will be 412 parts per million by volume, compared with 390 ppmv now. So Man will have added 22 ppmv by 2020, without any cuts in emissions. The CO2 concentration increase forestalled by almost a decade of cap-and-tax in Australia would thus be 2.5% of 1.5% of 22 ppmv, or 0.00825 ppmv. So in 2020 CO2 concentration would be 411.99175 ppmv instead of 412 ppmv.

So the proportionate change in CO2 concentration if the Commission and Ms. Gillard got their way would be 411.99175/412, or 0.99997998. The IPCC says warming or cooling, in Celsius degrees, is 3.7-5.7 times the logarithm of the proportionate change: central estimate 4.7. Also, it expects only 57% of manmade warming to occur by 2100: the rest would happen slowly and harmlessly over perhaps 1000 years (that's the real meaning of Flannery's 1000-year point, and it doesn't do him any favours).

So the warming forestalled by cutting Australia's emissions would be 57% of 4.7 times the logarithm of 0.99997998: that is - wait for it, wait for it - a dizzying 0.00005 Celsius, or around one-twenty-thousandth of a Celsius degree. Your estimate of a thousandth of a degree was a 20-fold exaggeration - not that Flannery was ever going to tell you that, of course.

Answer b) . Mutatis mutandis, we do the same calculation for the whole world, thus:

2.5% of 22 ppmv = 0.55 ppmv. Warming forestalled by 2020 = 0.57 x 4.7 ln[(412-0.55)/412] < 0.004 Celsius, or less than four one-thousandths of a Celsius degree, or around one-two-hundred-and-eightieth of a Celsius degree. And that at a cost of trillions. Whom the gods would destroy .

If you'd like chapter and verse from the IPCC's documents and from the peer-reviewed for every step of this calculation, which takes full account of and distils down the various complexities and probabilities Flannery flannelled about, you'll find it in this paper.

A cautionary note: the warming forestalled will only be this big if the IPCC's central estimate of the rate at which adding CO2 to the atmosphere causes warming is correct. However, it's at least a twofold exaggeration and probably more like fourfold. So divide both the above answers by, say, 3 to get what will still probably be an overestimate of the warming forestalled.


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