WASHINGTON -- "We're all Keynesians now," declared U.S. President Richard M. Nixon when he surrendered his fiscal policies to liberal orthodoxy. California Gov. Arnold Schwarzenegger did much the same with his recent executive order calling for draconian cuts in the emission of "greenhouse gases" linked to global warming. "The debate is over," he claimed.

The issue of global warming, though presented as a matter of scientific certainty, is actually highly controverted. Although the planet almost certainly is warming, how much of that is due to humanity -- which contributes only about 0.3 percent of total greenhouse gas emissions -- remains in dispute.

So does the likely magnitude of warming, as well as the ultimate impact on the climate. Over the last decade predictions of the temperature rise over the coming century have fallen greatly. Moreover, a modest temperature rise would lower morbidity and mortality rates and lengthen growing seasons.