"It depends on the choices made."
Where Americans live, what they drive, the food they eat, and things they value shape the country's ecological footprint, she explains.
(Related news: "Balance Earth's 'Eco Wealth' the Same Way as Finances, Group Says" [October 13, 2006].)
As the nation grows by 1 person every 11 seconds, those decisions lead to growing pressures on nature.
The CEP study says each American currently withdraws water at rates three times the world average; produces five pounds (2.2 kilograms) of trash per day, or five times the average in developing countries; and occupies 20 percent more land for housing, school, shopping, and other uses than the average American did two decades ago.
The 300 millionth American will find an increasingly suburbanized nation of low-density sprawl, the report concludes.
"Sprawl development is now the predominant form of land-use change," Markham said.
Spreading out rather than building up means Americans drive more, produce more greenhouse gases, and require more roads and land for malls, shops, and schools.
The study says 3,000 acres (1,214 hectares) of farmland are plowed under daily to meet suburbia's needs.
America's plump populace also eats what the study says are "disproportionately high amounts of meat and dairy products," foods that require more land, water, and energy than grain and vegetable-based diets.
In addition to the effects that America's growing population is having on the land, environmentalists are paying attention to where people are going.
More U.S. citizens are moving south and west, the study finds, shunning clustered development and cold climates for coastal zones.
Fifty-one percent of Americans now live 100 miles (161 kilometers) from a coast, according to the report.
These migration patterns put more people in the path of Mother Nature's wrath.
Farnsworth, the former Census Bureau head, notes that natural disasters will continue to reap greater tolls as more people move to previously uninhabited areas.
Most of the damage caused by Hurricane Katrina was done to homes built in the recent past, she said.
Increased migration to the coasts also forces coastal ecosystems to accommodate population density five times that of other geographic regions, Markham says.
The country's two population hot spotsthe South and the Westare already under environmental stress.
Of the ten states with the highest rates of plant and animal species extinction, seven are in the U.S. South, according to a 2002 study by NatureServe, a Virginia-based nonprofit.
The South is also the region with the highest number of mussel and fish species at risk of extinction, according to the CEP report.
The West, already saddled with water- and land-management problems, is the fastest growing region and the one where house sizes exceed the U.S. average.
Though the U.S. family has shrunk over the last 30 years, house sizes and the amount of land around them have grown, the report finds.
The average number of people per household fell from 3.1 in 1970 to 2.6 in 2000. Meanwhile, the average size of new single family homes grew by 700 square feet (65 square meters), the study says.
But the 300 millionth American may have a room of his or her ownin the second home of Baby Boomer grandparents.
Baby Boomersthose born in the decade following the end of World War IIare the biggest spenders and consumers in U.S. history, the CEP report finds.
"The Baby Boomer segment of the U.S. population has the highest natural resource use, and largest environmental impact of any generation," Markham said.
"They also have the highest rate of second home ownership."
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