WASHINGTON – America’s population is on track to hit 300 million this morning, and it’s causing a stir among environmentalists.

People in the United States are consuming more than ever – more food, more energy, more natural resources. Open spaces are shrinking and traffic in many areas is dreadful.

Three hundred million is still small potatoes compared to billion-plus giants India and China, which already had more than 300 million people a century ago.

But at least the United States, which is home to just under 1 in 20 of the 6.6 billion people worldwide, is still growing.

Fueled by economic growth and abundant immigration, America should add an additional 100 million people by the middle of the century.

That will be enough to keep the U.S. in the No. 3 slot on the world’s population chart as Indonesia, the No. 4 nation, plays catchup, according to the International Institute for Applied Systems Analysis, a nongovernmental research organization.

At the other end of the scale is tiny Vatican City, which has a population of just 770.

No. 2 on the little-land list is Tuvalu, a speck of sand in the South Pacific, with 10,000 people. Population growth isn’t a big issue there – the entire nation might have to move if global warming swamps the place.

Some experts argue that population growth only partly explains America’s growing consumption. Just as important, they say, is where people live, what they drive and how far they travel to work.

“The pattern of population growth is really the most crucial thing,” said Michael Replogle, transportation director for Environmental Defense, a New York-based advocacy group.

“If the population grows in thriving existing communities, restoring the historic density of older communities, we can easily sustain that growth and create a more efficient economy without sacrificing the environment,” Replogle said.

That has not been the American way. Instead, the country has fed its appetite for big houses, big yards, cul-de-sacs and strip malls. In a word: sprawl.

“Because the U.S. has become a suburban nation, sprawl has become the most predominant form of land use,” said Vicky Markham, director of the Center for Environment and Population, an advocacy group. “Sprawl is, by definition, more spread out. That of course requires more vehicles and more vehicle miles traveled.”

America still has a lot of wide-open spaces, with about 84 people per square mile, compared with about 300 people per square mile in the European Union and almost 900 people per square mile in Japan.

But a little more than half the U.S. population is clustered in counties along the coasts, including those along the Gulf of Mexico and the Great Lakes. Also, much of the population is moving away from large cities to the suburbs and beyond.

The fastest growing county is Flagler County, Fla., north of Daytona Beach; the fastest growing city is Elk Grove, Calif., a suburb of Sacramento; and the fastest growing metropolitan area is Riverside, Calif., about 50 miles east of Los Angeles.

“In New York City, people tend to think of that as an urban jungle, but the environmental impact per capita is quite low,” said Carlos Restrepo, a research scientist at New York University. “It tends to be less than it is for someone who lives in the suburbs with a big house where they need more than one car.”

The Census Bureau projects that America’s population will hit 300 million at 7:46 a.m. EDT today. 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 United States is one of the few Western nations that is still growing. With birthrates plunging, Europe and Russia are also losing people to the tune of about 100 million people in the next half-century, according to the research institute.

Overall, the planet is expected to have about 8 billion people by 2025 and 9.3 billion in 2050, give or take a few.

Almost all of the 80 million or so people being added to the world’s population per year in the next couple of decades will come from developing nations, especially in the South Asian subcontinent and sub-Saharan Africa.

India, blessed or cursed with higher fertility rates, is expected to overtake China somewhere around 2050 and become the world’s most populous nation.

Two of the fastest-growing countries in the next decades will be Nigeria and Pakistan. Both are expected to triple in population by 2050 to about 350 million apiece.

They will both pass today’s No. 5 nation, Brazil, which will level off at about 250 million people around the middle of the century.

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