Reports published in 2007 by the Intergovernmental Panel on Climate Change (IPCC) reflect a broad scientific consensus about the link between global warming and greenhouse gas emissions resulting from human activity. The report, while acknowledging that there is still uncertainty in the scientific estimates, calls for a reduction in annual emissions from just under 50 billion tons of greenhouse gases today to 5 billion to 10 billion or less by 2050, so that the planet warms by no more than two degrees centigrade. This report and similar reports from the scientific community have spurred political leaders around the world to action. The European Union has set targets to reduce its greenhouse gas emissions by 20 to 30 percent of the 1990 level as of 2020. Political leaders elsewhere are discussing similar goals. Some countries even say that they wish to become carbon neutral by 2050.

What will a significant reduction in the level of greenhouse gases entail? Which approaches will be most effective? How much will it cost to achieve this goal, both in money and in lifestyle changes? Who will bear that cost?

These questions lie at the center of heated debate among policy makers and stakeholders in many...