This summary updates Monckton of Brenchley (2013), read at the World Federation of Scientists’ 2012 Seminars

on Planetary Emergencies. For the first time, the paper combined mainstream IPCC climatology and inter-temporal

investment appraisal. The cost of Australia’s CO2 tax (Parliament of Australia, 2011) over its ten-year term was

compared with the benefit in the cost of warming-related damage avoided by the tax.

Discount rate: The minimum market discount rate is 5% (Murphy et al., 2008), but the rate assumed here is 0%.

Fraction of world CO2 emissions abated: Over ten years, the tax, which its inventor, Professor Garnaut, said

in 2013 had failed, cannot now abate more than 5% of predicted CO2 emissions. Australia emits 1.2% of world

emissions (derived from Boden et al., 2010ab). The tax will thus abate 5% x 1.2% = 0.06% of world emissions.

CO2 concentration abated: Without the tax, CO2 concentration after ten years would be 410 μatm (IPCC,

2007), up by 20 μatm on the 390 μatm (Conway & Tans, 2011) at the outset. With the tax, after ten years CO2

concentration would be 410 μatm less 0.06% of the 20 μatm growth: i.e. 409.988 μatm.

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CO2 forcing abated (IPCC, 2007; Myhre, 1998), would be 5.35 ln(410/409.988) = 0.00016 W m–2.

A climate sensitivity parameter is multiplied by this forcing to determine warming over the ten-year term.

Garnaut (2008) talks of keeping greenhouse-gas rises to 730 μatm CO2-equivalent, 450 μatm above the 280

μatm (IPCC, 2007) prevalent in 1750, to hold 21st-century warming since then to 2 Cº. His implicit 100-year

sensitivity parameter, in line with IPCC’s implicit 0.44 Cº W–1 m2, is thus 2 Cº / [5.35 ln(730/280) W m–2],

or 0.39 Cº W–1 m2, up by 0.08 Cº W–1 m2 on the instantaneous (Planck) parameter 0.31 Cº W–1 m2 (IPCC,

2007, p. 631 fn). Thus a reasonable ten-year parameter is 0.31 + 10/100(0.08) = 0.32-0.33 Cº W–1 m2.

Global warming abated by the tax – the ten-year parameter multiplied by the forcing abated – would be

0.33(0.00016) = 0.00005 Cº, or 1/20,000 Cº.

Measuring performance: Even if the tax succeeded, we could not detect that it had. 1/20,000 Cº, as a fraction

of the 0.05 Cº measurement uncertainty in temperature datasets, is just 1/1000 of that uncertainty.

The cost of the tax: The tax, as enacted in Australia’s Clean Energy Act 2011, is costong $10.1 bn/year, plus

$1.6 bn/year for administration (Wong, 2010, p. 5), plus $1.3 bn/year for renewables and other costs, a total of

$13 bn/year, escalated under the Act at 2%/year, and by a further 2%/year to allow for economic growth.

Conservatively, the total cost over the ten-year term will thus be $162.3 bn.

Mitigation cost-effectiveness of the tax, which is the cost of abating 1 Cº warming by global measures as costeffective as the tax, is $162.3 bn / 0.00005 Cº = $3.2 quadrillion per Cº abated.

Projected anthropogenic warming over the ten-year term will be 0.17 Cº (IPCC 2007, p. 803, Table 10.2).

The cost of abating 0.17 Cº warming by global measures as cost-effective as the tax is 0.17 x $3.2 quadrillion,

or $540 trillion in cash, which, divided by global population of 7 bn, is $77,000 per capita. Divided by ten

years’ global GDP of $670 trillion (derived from World Bank, 2011), it is equivalent to 80% of global GDP.

The benefit: Stern (2006, p. vi), estimates that the avoided-cost benefit of abating the 3 Cº 21st-century global

warming expected by the IPCC will be 0-3% of 21st-century global GDP. Since warming of 0.14 Cº/decade

observed in the 23 years since 1990 (HadCRUt3gl, 2011) is less than half the IPCC’s 3 Cº/decade central estimate,

a fair avoided-cost benefit is 1.5% of GDP.

Cost-benefit ratio: The cost of immediate mitigation divided by that of later adaptation is 80% / 1.5%, or 53. It

is at least 50 times more expensive and less cost-effective to mitigate CO2 emissions by typical measures such as

Australia’s carbon tax than to take no action at all today and, instead, to meet the later and far lesser cost of

climate-related damage arising from unabated global warming of 3 Cº the day after tomorrow.

2

References

Boden and Marland, 2010a. Global CO2 Emissions from Fossil-Fuel Burning, Cement Manufacture, and

Gas Flaring, 1751-2007. Carbon Dioxide Information and Analysis Center, Oak Ridge, Tennessee, USA.

Boden et al., 2010b. Ranking of the world’s countries by 2007 total CO2 emissions from fossil-fuel

burning, cement production, and gas flaring. Carbon Dioxide Information and Analysis Center, Oak Ridge,

Tennessee, USA.

Conway, T., & P. Tans, 2011, Recent trends in globally-averaged CO2 concentration, NOAA/ESRL,

http://www.esrl.noaa.gov/gmd/ccgg/trends/global.html#global.

Garnaut, R., 2008. The Garnaut Climate Change Review: Final Report. Cambridge University Press, Port

Melbourne, Australia, 680 pp, ISBN 9780521744447.

HadCRUt3gl, 2011. Monthly global mean surface temperature anomalies, 1850-2011.

http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3gl.txt.

IPCC, 2001. Climate Change 2001: The Scientific Basis: Contribution of Working Group I to the Third

Assessment Report of the Intergovernmental Panel on Climate Change [Houghton, J.T., Y. Ding, D.J. Griggs,

M. Noguer, P.J. van der Linden, X. Dai, K. Maskell and C.A. Johnson (eds.)]. Cambridge University Press,

Cambridge, United Kingdom, and New York, NY, USA.

IPCC, 2007. Climate Change 2007: the Physical Science Basis. Contribution of Working Group I to the

Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007 [Solomon, S., D. Qin, M.

Manning, Z. Chen, M. Marquis, K.B. Avery, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press,

Cambridge, United Kingdom, and New York, NY, USA.

Monckton of Brenchley, C.W., 2013. Is CO2 mitigation cost-effective? Proceedings of the 45th (2012)

Seminars on Planetary Emergencies, World Federation of Scientists, Geneva, Switzerland, and Erice, Sicily.

Murphy, 2008. Some Simple Economics of Climate Changes. Paper presented to the MPS General Meeting,

Tokyo, September 8.

Myhre et al., 1998. New estimates of radiative forcing due to well mixed greenhouse gases. Geophysical

Research Letters 25:14, 2715–2718, doi:10.1029/98GL01908.

Parliament of the Commonwealth of Australia, 2011, Exposure Draft of the Clean Energy Bill.

http://www.climatechange.gov.au/government/submissions/clean-energy-legislative-package/~/media/

publications/clean-energy-legislation/exposure-draft-clean-energy-bill-2011-pdf.pdf.

Stern, N., 2006, The Economics of Climate Change: The Stern Review. Cambridge University Press,

Cambridge, United Kingdom, and New York, NY, USA.

Wong, P., 2010. Portfolio Budget Statements 2010-11: Budget-Related Paper No. 1.4. Climate Change and

Energy Efficiency Portfolio, Commonwealth of Australia, Canberra, Australia.

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