In addition to comparing the two countries based on exchange rates, the IMF analysis also looked to the true, real-terms picture of the economies using "purchasing power parities." That compares what people earn and spend in real terms in their domestic economies.
Under PPP, the Chinese economy will expand from $11.2 trillion this year to $19 trillion in 2016. Meanwhile the size of the U.S. economy will rise from $15.2 trillion to $18.8 trillion. That would take America's share of the world output down to 17.7%, the lowest in modern times. China's would reach 18%, and rising.
Just 10 years ago, the U.S. economy was three times the size of China's.
Victor Cha, senior adviser on Asian affairs at Washington's Center for Strategic and International Studies, told me China's neighbors in Asia are already waking up to the dangers. "The region is overwhelmingly looking to the U.S. in a way that it hasn't done in the past," he said. "They see the U.S. as a counterweight to China. They also see American hegemony over the last half-century as fairly benign. In China they see the rise of an economic power that is not benevolent, that can be predatory. They don't see it as a benign hegemony."
The rise of China, and the relative decline of America, is the biggest story of our time. You can see its implications everywhere, from shuttered factories in the Midwest to soaring costs of oil and other commodities. Last fall, when I attended a conference in London about agricultural investment, I was struck by the number of people there who told stories about Chinese interests snapping up farmland and foodstuff supplies — from South America to China and elsewhere.