Uncertainty and climate change
I was at a conference on uncertainty and climate change in Berkeley last week, and gave the wrap-up panel discussion with Geoffrey Heal. We’d discussed a wide range of uncertainties and ambiguities, from future emissions scenarios to model uncertainty to perception and communication issues, and we were asked to comment on how, with so much uncertainty, economists can make useful recommendations.
Before I give the answer I came up with, a few side issues
First, as I mentioned briefly, while everyone at this workshop and many others were working on ways to reduce, manage and understand uncertainty, there is also a large and (at least until recently) very well-funded group working, to create and disseminate uncertainty, ignorance and confusion, with sufficient success that much of the political right in Australia and nearly all in the US have been (with their own complicity) deluded into thinking the problem is illusory.
Second, 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.
A third point, raised by Michael Hanemann is that the global average conceals a lot of seasonal and regional variation. He suggested IIRC that on current estimates, a 3.5 degree global average increase corresponds to an 8 degree increase in winter temperatures in Southern California, with huge implications for water supplies derived from snowfall.
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. Any agreement that comes out of Copenhagen or its successors will be better than no agreement.
A slightly trickier question is: what is the best target? I don’t have a good answer to this, but, given the politics of the process I don’t need one. The nature of such negotiations, with every country looking to shift as much of the cost as possible to others, ensures that there is almost no likelihood of getting an agreement that is too strong. In the present case, we can put some numbers on this. On the same kind of reasoning as I gave above, it seems clear enough that a 450 ppm target would be beneficial relative to a 550 ppm target. And, given the commitments and offers already on the table, the likelihood of anything stronger than 450 ppm is close to zero.
So, despite all the uncertainties, the policy position I would like to see Australia take to Copenhagen is clear enough. Aim for an agreement on a 450 ppm target, with emissions cuts on track for this until 2020 and with the capacity to revise later when we have more information. With all its imperfections, the currently proposed ETS (including a 25 per cent cut in emissions as part of a global agreement) is consistent with this position and therefore should be supported unless and until something better can be put in its place.