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The Census Bureau projects that America's population will hit 300 million at 7:46 a.m. EDT Tuesday. The projection is based on estimates for births, deaths and net immigration that add up to one new American every 11 seconds.
The estimated 11 million to 12 million illegal immigrants in the U.S. are included in official population estimates, though many demographers believe they are undercounted. The population reached its last milestone, 200 million, in 1967. That translates into a 50 percent increase in 39 years.
During the same period, the number of households nearly doubled, the number motor vehicles more than doubled and the miles driven in those vehicles nearly tripled. The average household size has shrunk from 3.3 people to 2.6 people, and the share of households with only one person has jumped from less than 16 percent to about 27 percent.
"The natural resource base that is required to support each person keeps rising," Replogle said. "We're heating and cooling more space, and the housing units are more spread out than ever before."
The U.S. is the third largest country in the world, behind China and India. The U.S. is the fastest growing of the industrialized nations, adding about 2.8 million people a year, or just under 1 percent. India is growing faster but the United Nations considers it to be a less developed country. About 40 percent of U.S. population growth comes from immigration, both legal and illegal, according to the Census Bureau. The rest comes from births outnumbering deaths.
"It's not the population, it's the consumption that can do us in," said William Frey, a demographer at the Brookings Institution, a Washington think tank. "These are the luxuries we have been able to support until now. But we're not going to be able to do it forever."