Adjusting for the time difference, the cost to the United States from a warmer climate at midcentury, according to the IPCC, would be at most 0.75 percent of gross domestic product, meaning that the costs of holding carbon dioxide to 1990 levels would be twice the gain from preventing any climate change. But the benefit-cost calculus is even worse. And if Third World nations, such as China, India, and Brazil, are exempted from the requirements of the treaty, Americans would pay a huge price for virtually no benefit. And even if the developing countries agreed to return emissions to 1990 levels, greenhouse gas concentrations would not be stabilized. Instead of saving the full 0.75 percent of gross domestic product by keeping emissions at 1990 levels, we would be saving much less.
Global change is inevitable.
Warmer is better. Richer is healthier. Whatever dangers global warming may pose, they will be most pronounced in the developing world. It is much easier for rich countries to adapt to any long-term shift in weather than it is for poor countries, which tend to be much more dependent on agriculture. Poor countries lack the resources to aid their flora and fauna in adapting, and many of their farmers earn too little to survive a shift to new conditions.