The Productivity Commission has just released a paper called The Stern Review: an assessment of its methodology (the full paper is a 1.3Mb PDF). It’s very good, I think, giving a balanced presentation to the Review, its supporters and critics and those who fit into neither category. Here’s the summary:

The Productivity Commission today released a staff working paper titled The Stern Review: an assessment of its methodology. This technical paper contains a detailed examination of key elements of the Review’s analytical approach. Originally prepared as an internal research memorandum following release of the Stern Review’s report, the paper is being made more widely available given its ongoing relevance in light of Australia’s Garnaut Review.

The staff paper finds that the Stern Review made some important analytical advances. The Review sought to move beyond analysis based on the mean expected outcome to one that incorporates low probability, but potentially catastrophic, events at the tail of probability distributions. The Review also attempted a more comprehensive coverage of damage costs than most previous studies.

The paper also finds that value judgements and ethical perspectives in key parts of the Stern Review’s analysis led to estimates of future economic damages being substantially higher, and abatement costs lower, than most previous studies. The paper notes that the report could usefully have included more sensitivity analysis to highlight to decisionmakers the consequences of alternative assumptions or judgements.

Looking at the way debate has evolved both within and outside the economics profession, a few points have emerged

* No-one credible now disputes the view that a well-designed set of policies could greatly reduce CO2 emissions at very low cost. The Stern Review is marginally lower than average at 1 per cent of GDP, but it would be hard to find any serious analyst claiming costs much higher than 3 per cent. These are once off changes in levels corresponding to a once-off loss of between a few months and one year of improvements in material living standards. It’s intuitively hard to see how risking the worst case outcomes of climate change to avoid such a small economic cost could possibly be justified.

* While there is still plenty of dispute about the economic costs of doing nothing, relative to stabilisation, the median estimate has been revised sharply upwards following the Stern Review. On the issue of discount rates, the (still controversial) choice of a low rate by the Stern Review pointed up the dependence of earlier estimates on rates that now look implausibly high. And on the treatment of risk and damage to the natural environment, Stern’s look at these issues points up how badly neglected they were in the past. If anything, subsequent discussion has suggested that Stern was too conservative.

The speed with which the economic debate has evolved has left the political advocates of doing little or nothing stranded. Most of them had no qualifications in climate science, and embraced delusionist arguments against the science because they were opposed on political, economic or culture-war grounds to the kinds of policies needed to stabilise climate. Many of them clearly envisaged a campaign in which they would fight as long as possible on the science before turning to the economics. But the speed of change has left them flatfooted. Rather than being able to make a graceful retreat to a prepared position, they are trying to argue against what is now the mainstream economics position, while still being lumbered with their now-discredited attacks on mainstream science.