Tuesday, November 14, 2006

The Stern Review

A few weeks ago the British government put out a report about climate change, entitled "The Stern Review" which made quite a splash. BBC News reported:
Global warming could cut the world's annual economic output by as much as 20%, an influential report by Sir Nicholas Stern is expected to say.
While that is a worst case scenario, the report claims that at the very best the cost of tackling global warming would be 1% of annual economic output.
Sir Nicholas's comments are expected to form the core of The Stern Review that is due to be released on Monday.
A summary and the whole document can be found here. In an essay for the Wall Street Journal (via The Volokh Conspiracy), Bjørn Lomborg explains why this report is deeply flawed:
The review correctly points out that climate change is a real problem, and that it is caused by human greenhouse-gas emissions. Little else is right, however, and the report seems hastily put-together, with many sloppy errors. As an example, the cost of hurricanes in the U.S. is said to be both 0.13% of U.S. GDP and 10 times that figure.
The review is also one-sided, focusing almost exclusively on carbon-emission cuts as the solution to the problem of climate change. Mr. Stern sees increasing hurricane damage in the U.S. as a powerful argument for carbon controls. However, hurricane damage is increasing predominantly because there are more people with more goods to be damaged, settling in ever more risky habitats. Even if global warming does significantly increase the power of hurricanes, it is estimated that 95% to 98% of the increased damage will be due to demographics. The review acknowledges that simple initiatives like bracing and securing roof trusses and walls can cheaply reduce damage by more than 80%; yet its policy recommendations on expensive carbon reductions promise to cut the damages by 1% to 2% at best. That is a bad deal.
Mr. Stern is also selective, often seeming to cherry-pick statistics to fit an argument. This is demonstrated most clearly in the review's examination of the social damage costs of CO2--essentially the environmental cost of emitting each extra ton of CO2. The most well-recognized climate economist in the world is probably Yale University's William Nordhaus, whose "approach is perhaps closest in spirit to ours," according to the Stern review. Mr. Nordhaus finds that the social cost of CO2 is $2.50 per ton. Mr. Stern, however, uses a figure of $85 per ton. Picking a rate even higher than the official U.K. estimates--that have themselves been criticized for being over the top--speaks volumes.
But nowhere is the imbalance clearer than in Mr. Stern's central argument about the costs and benefits of action on climate change. The review tells us that we should make significant cuts in carbon emissions to stabilize the concentration of atmospheric carbon dioxide at 550 ppm (parts per million). Yet such a stark recommendation is not matched by an explicit explanation of what this would mean in terms of temperature.
The U.N. Climate Panel estimates that stabilizing at 550 ppm would mean an increase in temperature of about 2.3 degrees Celsius in the year 2100. This might be several degrees below what would otherwise happen, but it might also be higher. Mr. Nordhaus estimates that the stabilization policy would reduce the rise in temperature from 2.53 degrees Celsius to just 2.42 degrees Celsius. One can understand the reluctance of the Stern review to advertise such a puny effect.
The Stern review's cornerstone argument for immediate and strong action now is based on the suggestion that doing nothing about climate change costs 20% of GDP now, and doing something only costs 1%. However, this argument hinges on three very problematic assumptions.
First, it assumes that if we act, we will not still have to pay. But this is not so--Mr. Stern actually tells us that his solution is "already associated with significant risks." Second, it requires the cost of action to be as cheap as he tells us--and on this front his numbers are at best overly optimistic. Third, and most importantly, it requires the cost of doing nothing to be a realistic assumption: But the 20% of GDP figure is inflated by an unrealistically pessimistic vision of the 22nd century, and by an extreme and unrealistically low discount rate. According to the background numbers in Mr. Stern's own report, climate change will cost us 0% now and 3% of GDP in 2100, a much more informative number than the 20% now and forever.
In other words: Given reasonable inputs, most cost-benefit models show that dramatic and early carbon reductions cost more than the good they do. Mr. Stern's attempt to challenge that understanding is based on a chain of unlikely assumptions.
Faced with such alarmist suggestions, spending just 1% of GDP or $450 billion each year to cut carbon emissions seems on the surface like a sound investment. In fact, it is one of the least attractive options. Spending just a fraction of this figure--$75 billion--the U.N. estimates that we could solve all the world's major basic problems. We could give everyone clean drinking water, sanitation, basic health care and education right now. Is that not better?
We know from economic models that dealing just with malaria could provide economic boosts to the order of 1% extra GDP growth per capita per year. Even making a very conservative estimate that solving all the major basic issues would induce just 2% extra growth, 100 years from now each individual in the developing world would be more than 700% richer. That truly trivializes Mr. Stern's 10% to 13% estimates for South Asia and Sub-Saharan Africa.
Do read the whole thing. Quite a few people, not all of them so-called climate skeptics, seem to be unhappy about the report. Philip Stott comments here, Roger A. Pielke, Jr. notes some cherry-picking here, James Annan has a "stern review of the Stern Review" and see here for more. Even the UN's upcoming IPCC report seems to contradict Stern's claims. I have to say that I hope Professor Stott is correct:
I predict that Stern will sink quite quickly to join the now-forgotten Population Bomb and Limits to Growth, and many other such doomsday tracts.
Otherwise, we'll see what people think when it hits them in the pocket.

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