Bjorn to Run (Numbers)

The immortal Bjorn Lomborg takes on a new study claiming global warming will cost 20 percent of global GDP if left unchecked, in today's Wall Street Journal (free). There's a reason Lomborg is the most famous Skeptical Environmentalist out there–his takedown is very clear, very thorough, calmly rational, and completely devastating:

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.

Lomborg also reports on another round of 2004's Copenhagen Consensus experiment, with the same results as last time:

Last weekend in New York, I asked 24 U.N. ambassadors–from nations including China, India and the U.S.–to prioritize the best solutions for the world's greatest challenges, in a project known as Copenhagen Consensus. They looked at what spending money to combat climate change and other major problems could achieve. They found that the world should prioritize the need for better health, nutrition, water, sanitation and education, long before we turn our attention to the costly mitigation of global warning.

Read the whole thing here, or read 540 pages of kickass analysis on the same point here.