After seven years in critical condition, the Kyoto global warming treaty has a new lease on life, thanks to its recent ratification by Russia. Supporters and skeptics alike agree that the treaty will not solve the climate problem. Its environmental limits are meager, expire in 2012 and do not apply to developing nations, where global warming emissions are growing most rapidly. Kyoto's true importance rests in what it tells us about America's changing relationship with the world and the future of climate change diplomacy.

Kyoto demonstrates that America's allies are increasingly shaping the international agenda without it. When the Bush administration rejected Kyoto in 2001, it assumed that other nations would follow suit, but more than 120 nations have ratified it.

While Europe's inability in the 1990s to stop ethnic cleansing in the Balkans reinforced its junior partner status on security matters, Kyoto shows that Europe can lead in other areas. The European Union, fresh from its successful eastward enlargement, feels increasingly confident as an international peer of the United States on nonmilitary matters. Complying with Kyoto may prove more difficult than Europe envisions, but Europe has achieved what it regards as a major foreign policy victory and this signals the growing risk of an even sharper-edged trans-Atlantic rivalry.

Kyoto also illustrates the fact that the international community questions more than ever America's moral authority and its commitment to universal values, including environmental stewardship. Anti-Americanism is already on the rise in "old Europe" because of Bush's policies on Iraq. U.S. resistance to action on global warming only solidifies America's image abroad as a nation of parochial, selfish and wasteful SUV drivers. Although America remains the brightest beacon of freedom, it must treat seriously the perception abroad that its light has dimmed.

Kyoto's rebirth reaffirms, in addition, that climate change will remain a permanent fixture of international diplomacy, thus signaling to U.S. industry that strong federal action is inevitable even as Bush's re-election lengthens its current reprieve. The coming into force of the treaty increases pressure on the United States to lead even as it remains outside the treaty's ambit. The United States, after all, is responsible for just under a quarter of global climate emissions. Opposition from industry to mandatory domestic climate action will not dissipate overnight, but Kyoto's implementation abroad will demonstrate the true cost of climate policies and help U.S. policymakers determine what action is economically feasible.

Finally, Kyoto makes it more likely that over the next decade Europe will use trade policy to push the United States toward stronger climate action. The European Parliament has debated taxing U.S. imports to protect domestic manufactures from foreign competitors who are not subject to climate change costs. The World Trade Organization has made clear that when an environmental trade restraint is enacted to implement a multilateral environmental agreement such as Kyoto, the restraint is more likely to withstand scrutiny.

Given Bush's unalterable opposition to the treaty, the United States is unlikely to rejoin international talks anytime soon. That matters less, however, than whether the United States begins to take seriously its responsibility to lead the world through strong new domestic climate policies. Leaving aside the environmental rationale for Kyoto, the treaty's entry into force is a warning of the political and economic risks to the United States of continued inaction.

Nigel Purvis, an environment scholar at the Brookings Institution in Washington, served as a senior climate change negotiator in the Clinton and George W. Bush administrations.