There is a new report on global warming done by the reputable economist Nicholas Stern. The Stern Review's conclusion (tip to Instapundit and TCS):

Using the results from formal economic models, the Review estimates that if we don't act, the overall costs and risks of climate change will be equivalent to losing at least 5% of global GDP each year, now and forever. If a wider range of risks and impacts is taken into account, the estimates of damage could rise to 20% of GDP or more.

In contrast, the costs of action — reducing greenhouse gas emissions to avoid the worst impacts of climate change — can be limited to around 1% of global GDP each year."

Bjorn Lomborg dissects the Stern Review at Opinion Journal (tip to Tim Blair):

The report on climate change by Nicholas Stern and the U.K. government has sparked publicity and scary headlines around the world. Much attention has been devoted to Mr. Stern's core argument that the price of inaction would be extraordinary and the cost of action modest.

Unfortunately, this claim falls apart when one actually reads the 700-page tome. Despite using many good references, the Stern Review on the Economics of Climate Change is selective and its conclusion flawed. Its fear-mongering arguments have been sensationalized, which is ultimately only likely to make the world worse off. . . .

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. . . .

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.

Most economists were surprised by Mr. Stern's large economic estimates of damage from global warming. Mr. Nordhaus's model, for example, anticipates 3% will be wiped off global GDP if nothing is done over the coming century, taking into account the risk for catastrophes. The Stern review purports to show that the cost is "larger than many earlier studies suggested." . . .

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.

You should read both the executive summary of the Stern Report and Lomborg's review.

I did find one part of Lomborg's critique unrealistically sanguine. Lomborg accepts the UN's estimated cost of providing even the most "basic" health care to the world, $75 billion, which strikes me as awfully low: How could $12 a year per person per year pay for basic health care, education, and clean drinking water where it is not now provided?

Overall, I will never understand why the very real problem of global warming turns otherwise sensible people into fear-mongers.