Carbon offsets don't add up

George Monbiot runs the math. His conclusion: "The rich can relax. We just need the poor world to cut emissions. By 125%."

As the G8 leaders know, a global cut of 50% [by 2050] offers only a faint to nonexistent chance of meeting their ultimate objective: preventing more than two degrees of warming. In its latest summary of climate science, published in 2007, the Intergovernmental Panel on Climate Change suggested that a high chance of preventing more than two degrees of warming requires a global cut of 85% by 2050. In drafting the climate change act, the UK government promised to keep matching the target to the science. It has already raised its cut from 60% to 80% by 2050. If it sticks to its promise it will have to raise it again.

Global average CO2 emissions are 4.48 tonnes per person per year. Cutting the world total by 85% means reducing this to 0.67 tonnes. Average per capita output in the 38 Annex 1 countries is 10 tonnes; to hit this target they must cut their emissions by 93.3% by 2050. If the rich persist in offsetting 50% of this cut, the poorer countries would have to reduce their emissions by 7bn tonnes to absorb our offsets. To meet a global average of 0.67 tonnes, they would also need to chop their own output by a further 10.8bn tonnes. This means a total cut of 17.8bn tonnes, or 125% of their current emissions. I hope you have spotted the flaw

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Carbon offsetting makes sense if you are seeking a global cut of 5% between now and for ever. It is the cheapest and quickest way of achieving an insignificant reduction. But as soon as you seek substantial cuts, it becomes an unfair, impossible nonsense, the equivalent of pulling yourself off the ground by your whiskers. Yes, let us help poorer nations to reduce deforestation and clean up pollution. But let us not pretend that it lets us off the hook.