SHANGHAI--To drive through the Yan'an tunnel that separates the old neighborhoods of Shanghai from the new Pudong district is to travel not so much through space as through time. Pudong's science-fiction skyline of massive and exotically shaped office towers gleams like a postcard from the 22nd century.

Bill Emmott, the former editor of The Economist, writes in his insightful and deeply reported new book, Rivals, that "the shift in economic and political power to Asia" remains "the most important long-term trend in world affairs." Shanghai is a monument in glass and steel to the power of that judgment.

Shanghai is also a monument to the environmental challenge that dynamism presents. Its streets are perpetually clogged with cars and trucks. Its skyscrapers demand vast supplies of electricity for cooling and lighting. The sky often droops over the city--heavy and gray. In all these ways, Shanghai testifies to the pressures that have propelled China past the United States as the world's largest emitter of carbon dioxide and the other gases linked to global warming. Finding ways to balance China's need for energy to fuel its growth with the imperative to reduce those emissions worldwide is what promises to be the next great challenge in America's relations with this vast and vibrant power.

Today those relations are relatively placid. Despite intermittent flare-ups over trade and human rights, China has provoked remarkably little discussion in the 2008 presidential campaign. And although interest in the American election is considerable in China as well as in Japan, conversations last week with business leaders, academics, and international-affairs analysts in both nations found surprisingly little concern that its outcome will matter much to the region.

In both countries, presumptive Democratic nominee Barack Obama has stirred excitement among many young people. But in both nations, many observers think that elite opinion tilts toward presumptive Republican nominee John McCain. That's largely because, in Shanghai and Tokyo alike , President Bush is given credit for maintaining positive relations with China and Japan simultaneously--no easy task. He is also credited with opening doors to India, the region's third giant, and easing (however fitfully) tensions with North Korea. A senior Chinese foreign-policy analyst expressed a view common among the experts I met with in Tokyo as well: "In terms of Asia policy, whether there is a President Obama or a President McCain, [he] will largely carry on the legacy from President Bush."

That could be true in many ways (although a President Obama, given the constituencies important to him, would inevitably pressure China on trade and human rights more than Bush or McCain). But in one significant, and combustible, respect, the Asian expectation of continuity is misplaced.

Bush, because he opposes mandatory cuts in greenhouse-gas emissions, made it easy for China (and also India) to reject limits as well. But Obama and McCain are committed to compulsory U.S. reductions. And both recognize that Congress is unlikely to approve such limits unless China and India accept (as Japan already has) an international agreement to reduce their own emissions.

Nudging China into such an agreement wouldn't be easy. The frustration over the country's environmental degradation is growing, especially among younger Chinese. But the sheer scale of China's economic transformation makes carbon reductions a daunting challenge: The International Energy Agency recently projected that China and India alone will account for nearly half of the world's increased energy use through 2030. And after Bush exerted so little pressure on China, even that nation's experts on U.S. politics seem genuinely surprised that the next president might turn up the heat on global warming.

Although China now leads the world in total greenhouse emissions, America's per capita pollution remains nearly four times as great. With that in mind, the next president will undoubtedly offer China carrots on climate change, like the farsighted 10-year agreement on environmental cooperation that Bush signed with Beijing this month.

But the next president will also be more willing than Bush has been to brandish sticks, such as the proposal in this month's failed Senate climate bill to eventually impose a "carbon tariff" on imports from nations that don't limit greenhouse emissions. That prospect stunned and disturbed the Chinese. Their reaction suggests that the (relative) tranquility in U.S.-China relations today may be just the calm before a climate-induced storm.

This article appeared in the Saturday, June 28, 2008 edition of National Journal.

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