The U.S. GDP is now about 22% of the global total, and very likely to keep declining in the next few decades. But policy discussions in the U.S. often don't really come to grips with the fact that the U.S. has limited power in this globalizing economy. Here are a few examples.
Concerning climate change policy: Here's a recent report from Reuters on China's announcements about expanding coal production. "China approved the construction of more than 100 million tonnes of new coal production capacity in 2013 - six times more than a year earlier and equal to 10 percent of U.S. annual usage - flying in the face of plans to tackle choking air pollution. The scale of the increase, which only includes major mines, reflects Beijing's aim to put 860 million tonnes of new coal production capacity into operation over the five years to 2015, more than the entire annual output of India." While U.S. can (and should) argue about appropriate policies to address carbon emissions, choices made in the U.S. and Europe will not be the primary determinants of future carbon emissions.
Concerning corporate taxation: American citizens and politicians can argue all they want about what it is "fair" for corporations to pay in taxes, but in an economy with global supply chains and rising trade, corporations will inevitably have greater power to shift operations and use accounting to move profits between jurisdictions. Signing some international agreements about corporate taxation won't change this basic fact. If you want to tax high-income people, then it makes more sense to focus on their tax rates, rather than trying to tax corporation.
Concerning the directions of future technology growth: Here in America we like to have arguments over what kind of research on, say, genetic issues or using human tissue should be acceptable. But the U.S. share of global R&D fell from 38% in 1999 to 32% by 2009. China has now outstripped Japan for second place in global R&D spending, and China's R&D spending is similar to that of Germany, France, and Italy combined. A report just published in the New England Journal of Medicine notes that U.S. biomedical R&D spending dropped from 2007-2010, while the world total is rising. In the past, the rest of the world sometimes complained that global R&D was dominated by U.S. priorities. This complaint will be less true in the future.
Concerning blockbuster movies: The rest of the world used to complain, with some justice, that they were forcefed a diet of mass entertainment based first and foremost on the desires of U.S. customers. But now blockbuster movies are made with the global market in mind. Superheroes, cartoons, robots, global crime, and natural disaster play well everywhere.
Concerning globalization itself: When the subject of trade agreements comes up, like the Trans-Pacific Partnership, Transatlantic Trade and Investment Partnership, and Trade in Services Agreement, the tone of the discussion often seems to imply that U.S. policymakers are deciding on the future of globalization. But they are not. Globalization is speeding ahead without any permission from them, based on advances in transportation, information, and communications technology, along with actions by other countries. Trade policy is only trying to shape the direction of globalization a bit, and to negotiate around the margins some of the terms under which globalization will proceed.
Just to be clear, the U.S. economy is not becoming a economic minnow like Belize or Burundi. But 65 years ago, as the high-income countries climbed out of the wreckage left by World War II and today's emerging economies had not yet engaged in the global economy, the U.S. economy had an extraordinary time of dominance. For a time in the 1960s, it was common to hear that the planned economy of the USSR would outstrip the U.S. economy. In the 1970s and into the 1980, Japan was going to rule the world economy. Around 2000 and the launch of the euro, there was talk about the economic rise of the European Union. But now, we are seeing the rise of a multipolar and distributed world economy, with faster growth happening in the emerging economies, but with stronger linkages of trade and global supply chains reaching across the world economy. The U.S. can certainly be an active and leading participant in shaping the world's economic future. But neither the U.S., nor some combination of high-income countries around the world, has the power to dictate what configurations will emerge.