Leadership matters when it comes to greenery because solving most environmental issues requires a change in direction. Leaders can send signals and forge new paths. But in the area where the world thinks a single leader towers above all—namely the choice of the next American president—leadership actually matters a lot less. America's president is powerful, to be sure, but American politics has been fragmenting over the last few decades. Alone, the president often has a weak impact on real American policies that affect the environment.

The U.S. record on international environmental issues is highly uneven for reasons that have little to do with George W. Bush's leadership. His administration has been tarred across the planet for reckless leadership on international environmental issues. (Its actual record, while dreadful, is not a uniform failure. It has done useful things in a few areas, such as a thoughtful initiative to help conserve forests in the Congo Basin.) But the signature of Bush's reckless foreign policy in this area, his decision to withdraw from the Kyoto treaty barely three months after taking office, actually has its roots in the Clinton administration. Clinton was highly committed to environmental issues and his vice president, Al Gore, was an even more passionate leader. Their zealous diplomats negotiated a treaty that was larded with commitments that the United States never could have honored. The promise to cut U.S. emissions 7 percent below 1990 levels is a good example. Because actual emissions were rising steadily, it would have been impractical to turn them around in time to meet the 2012 Kyoto deadline. The U.S. Congress never could have passed the requisite legislation, and no leader in the White House could have changed that voting arithmetic. The U.S. withdrawal from the Kyoto Protocol was inevitable.

What does this mean for America's credibility in the world? When the American president promises, should anyone listen?

Increasingly, other countries are learning that the answer is no—because American leaders have a habit of promising a lot more than they can deliver. Environmental issues are particularly prone to overpromising, and not just by the United States. Europe, too, is fresh with unrealistic claims by political leaders. The European Union, for example, has launched negotiations for the post-Kyoto agreement by claiming that Europeans will cut greenhouse-gas emissions 20 percent to 30 percent by 2020—an outrageous goal considering that most of Europe (with the exception mainly of Britain and Germany) will fail to meet their existing targets, and emissions are actually rising. Europe as a whole would blow through its Kyoto targets if not for its generous use of a scheme that lets them take credit for overseas investment in low-carbon technologies—despite mounting evidence that many of those overseas credits don't actually deliver real reductions in emissions. Smart politicians know that the benefits lie mainly in the promising today and not in the delivery long in the future.

Ironically, the more enthusiastic the leader, the less credibility he or she has. While the Clinton administration was busy negotiating the Kyoto treaty, the U.S. Senate was passing a resolution, 95 to 0, to signal that it would reject any treaty that didn't contain specific commitments by developing countries to control their effluent of greenhouse gases. Since the developing countries had already rejected that outcome the Clinton administration had little room to maneuver. The great reversal in U.S. "leadership" on global warming over the last year—signaled by President Bush's speech three weeks ago embracing the need for limits on greenhouse gases—came from the people rather than top leaders. Public concern about global warming is rising (though it will be checked by the even more acute worries on the economy and war). The Bush speech was more a recognition that serious efforts to develop climate legislation are already well underway without his stamp. Many states are already planning to regulate greenhouse gases. The Senate has a serious bill on this subject scheduled for floor debate starting June 2. Its sponsors are Joe Lieberman (the former running mate of Al Gore but now alienated from the Democratic Party for his overly independent views) and John Warner (a Republican who has no former track record on global warming). These are ideal leaders for this issue because often it takes the fresh faces focused on building bipartisan majorities to get things done in America.

Perhaps the most interesting signal that American presidents are losing the ability to lead is an effort to rewrite the rules that would govern environmental treaties under American law. Committed environmentalists have rightly noted that America's Constitution requires a two-thirds vote for treaties in the Senate. That standard is nearly impossible to meet because one third of the Senate is usually opposed to anything interesting. Serious efforts are now underway to reinterpret environmental "treaties" as agreements between Congress and the president, which would require only a majority vote. Most trade agreements, for example, travel under this more lax standard and also have special voting rules that require Congress to approve the agreement as a whole package rather than pick it apart piece by piece. Rebranding and changing voting rules makes it easier to approve agreements, boosting the credibility of the president to negotiate agreements that serve the country's interest.