Uncertainty and climate change

Australian Economist, John Quiggin points out that uncertainty should increase intensity of climate change action.  He writes

…it’s a straightforward implication of standard economic analysis that the more uncertainty is the rate of climate change the stronger is the optimal policy response. That’s because, in the economic jargon, the damage function is convex. To explain this, think about the central IPCC projection of a 3.5 degrees increase in global mean temperature, which would imply significant but moderate economic damage (maybe a long-run loss of 5-10 per cent of GDP, depending on how you value ecosystem effects). In the most optimistic case, that might be totally wrong – there might be no warming and no damage. But precisely because this is a central projection it implies an equal probability that the warming will be 7 degrees, which would be utterly catastrophic. So, a calculation that takes account of uncertainty implies greater expected losses from inaction and therefore a stronger case for action. This is partly offset by the fact that we will learn more over time, so an optimal plan may involve an initial period where the reduction in emissions is slower, but there is an investment in capacity to reduce emissions quickly if the news is bad. This is why its important to get an emissions trading scheme in place, with details that can be adjusted later, rather than to argue too much about getting the short term parts of the policy exactly right.

Anyway, back to my main point. The huge scientific uncertainty about the cost of inaction has obscured a surprisingly strong economic consensus about the economic cost of stabilising global CO2 concentrations at the levels currently being debated by national governments, that is, in the range 450-550 ppm. The typical estimate of costs is 2 per cent of global income, plus or minus 2 per cent. There are no credible estimates above 5 per cent, and I don’t think any serious economist believes in a value below zero (that is, a claim that we could eliminate most CO2 emissions using only ‘no regrets’ policies).

For anyone who, like me, is confident that the expected costs of doing nothing about emissions, relative to stabilisation, are well above 5 per cent of global income that makes the basic choice an easy one.

One thought on “Uncertainty and climate change”

  1. I just discovered this site and I’m very impressed and inspired. I agree that uncertainity should increase our intensity and sense of urgency in response to climate change. I’m concerned, though, that governments are still using 450-550 ppm as an acceptable level. The recent findings by the IPCC about the increased rate of climate change, beyond what was originally predicted, indicates to me that Bill McKibben and others are right in drawing the line at 350 ppm. Anything above that and it becomes more and more certain that climate change will be catastrophic and probably not reversable.

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