US can't dodge global slowdown forever

US economy doing just fine: Pro
US economy doing just fine: Pro   

As the gears of the global economy continue to slow, the U.S. has—so far—bucked the trend.

But it can't do so forever.

"The world is counting on the U.S. economy to drive the global recovery," Treasury Secretary Jack Lew said last week ahead of a meeting of G-20 leaders.

"But the global economy cannot prosper broadly relying on the United States to be the importer of first and last resort, nor can it rely on the United States to grow fast enough to make up for weak growth in major world economies."

Read MoreCheap credit in Europe, China: Too little, too late?

Since the Great Recession lifted nearly four years ago, the economies of the developing world have been slowly getting back on their feet. The recovery has been fueled in part by massive monetary stimulus, chiefly from the U.S. Federal Reserve, which has pushed interest rates lower, and for longer, than at any time in its 100-year history.

Until recently, global growth has also been bolstered by China's red-hot economy and its nearly insatiable demand for both raw materials from developing countries and autos, computers and high-end luxury goods made in the U.S. and Europe.

But China's growth is slowing, and most of the rest of the world is mired in what appears to be a deepening slump. An Associated Press survey of 30 economists recently found that 57 percent of them expect China's decelerating economy to dampen growth from Brazil and Chile to Australia and South Korea.

For now, the economists see the U.S. as largely insulated from China's troubles. After the Great Recession sparked a wave of layoffs and foreclosures, both the job and housing markets have slowly but steadily rebounded. Lower oil prices have helped boost household budgets and corporate profits. The U.S. stock market continues to set new highs.

But the longer-term outlook in the advanced economies of the world is clouded by a demographic shift that has been building for decades—and shows no signs of reversal. The impact of aging populationsmost notably in Japanhas created powerful economic strains that are weighing on growth.

The effect is being felt most heavily in Japan, which has embarked on a two-year plan to jump-start growth after back to back "lost decades" of stagnation. Labor force growth has been faster in Europe and the U.S., but it is slowing markedly from the 1970s and 1980s when baby boomers entered the workforce in large numbers.

'For Japan, this is the beginning of the end': Pro
'For Japan, this is the beginning of the end': Pro   

While the developed world struggles with stagnant economies, the emerging markets of Asia, South America and Africa are expected to outpace advanced economies in the coming decades. Higher birthrates, rising wages and a rapidly expanding middle class are expected to boost consumption in the next 20 to 30 years.

"Developing economies excluding China, which account for roughly 40 percent of global GDP, should grow nearly 5 percent supported, in part, by solid population growth," according to Wells Fargo Securities global economist Jay Bryson.

For now, U.S. policymakers are relying on the Federal Reserve's easy money credit policies to keep the economy growing. But some economists contend that a more sustainable stimulus could be found in the controversial policy to ease immigration restrictions, allowing more working-age immigrants to come to the U.S. and contribute to overall wage growth and tax revenues.

Read More EU to Japan: Drink more beer

If it becomes law, for example, last year's Senate immigration reform bill would bring some 10.4 million new residents to the U.S. by 2023, according to a 2013 CBO study. Those new arrivals would add roughly 3.3 percent to U.S. gross domestic product by 2023 and 5.44 percent by 2033, compared with the CBO's growth estimates without immigration reform.

Those new residents would also create demand for more government servicescosting taxpayers roughly $262 billion through 2033.

But the increase in wages from those new workers would generate roughly $459 billion in new tax revenues through the same period, according to the CBO.