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More on Emissions

Tuesday, 23rd October 2007

The Times tells us that:

Carbon dioxide levels in the atmosphere are increasing much faster and will be harder to control than scientists have predicted, a study has found.

An international team of researchers has found that, since 2000, the rate at which CO2 has been pumped into the atmosphere is 35 per cent greater than most climate change models have allowed for.

The important word there is "most". The IPCC scenarios, the ideas of how the economy might develop, are forty in number. They are grouped into four families (all the boring detail is here). The point of these economic models is to work out what emissions will be: these are then fed into the actual climate models to give us an idea of what is likely to happen. When these scenarios were drawn up in the 90s we didn't actually know which of them were likely to come true: they're guesses, if informed ones. We're specifically told that we cannot assign any probability to one or the other happening. OK, prediction, especially about the future, is very difficult.

But we've now had nearly a decade since those models were assembled. We can look at what has actually been happening and refine our probabilities, from none, to something a little more accurate. This is where the "most" becomes important. For the emissions we're seeing in the real world closely track the so called "A1" family. This has it's pros and cons: higher emissions, yes, but a population that peaks at 2050 then declines and a vastly richer (four times per capita) world in 2100 than the A2 family. In fact, average global per capita GDP above the current US level.

Now what we might do about all of this really does rather depend upon which economic path we are going down: a vastly richer world in the future argues perhaps for more adaptation (for if it should indeed be the rich who pay and the rich are those in the future then it should be they who adapt rather than us who reduce emissions) than amelioration.

But perhaps the most important point about this new finding upon emissions is that we can now safely ignore the Stern Review. It is based, in its entirety, on the idea that we will be following the A2 family of emissions and economic growth. We're not, and as Keynes pointed out, when the facts change we should change our minds.