The next 100 million and the face of America

The one sure thing about US population as it moves past 300 million – expected to happen in the next few days – is that there will be more Americans. A lot more.

Everything else is informed speculation. Still, much will turn on how big the United States becomes and how fast it grows – from its use of natural resources to its settlement patterns to shifts in political clout.

There will be 400 million Americans in 2043, climbing to 420 million by midcentury, the US Census Bureau estimates. The added numbers will change the nature of the populace, reflecting trends already begun.

Between the last official census in 2000 and the one of 2050, non-Hispanic whites will have dwindled from 69 percent to a bare majority of 50.1 percent. The share who are Hispanic will have doubled to 24 percent. Asians also will have doubled to 8 percent of the population. African-Americans will have edged up to 14 percent. In other words, the US will be on the verge of becoming a "majority of minorities."

Wars, natural disasters, shifts in the economy, unforeseen social and political developments – any or all of these could affect the numbers, perhaps dramatically. For one thing, America could, as many voters and their elected officials now demand, clamp down on immigration. The country's unusually high teen pregnancy rate could drop. Scientific advances could extend longevity.

In any case, Americans are expected to continue to gravitate west and south. Today, the Top 10 fastest growing states, cities, and metropolitan areas are all in those regions, mostly in the West. In general, the West and South have been growing two to three times as fast as the Northeast and Midwest.

The great American midsection, meanwhile, will continue to empty out.

When historian Frederick Jackson Turner declared the American frontier "closed" in 1893, he was using the Census Bureau definition of "frontier" as areas having no more than six people per square mile. By that same density definition, the number of such counties actually has been increasing: from 388 in 1980 to 397 in 1990 to 402 in 2000. Kansas has more "frontier" land now than it did in 1890.

If these regional shifts continue as expected, the political impact will be felt. For one thing, membership in the US House of Representatives, fixed at 435 seats, would change, producing winners and losers just as it has with recent censuses. It may shift the current alignment of "red" states and "blue" states – but other factors besides population growth in the South and West may influence that political balance.

For example, wealthy, relatively liberal Californians and others with money to spend have been buying up ranch land in politically conservative Rocky Mountain states such as Montana, Idaho, and Wyoming. Many of them are more inclined to want to protect the environment from energy exploration and other development.

An increasing Hispanic population – which could see 188 percent growth between 2000 and 2050, according to the Census Bureau – could affect the political balance as well.

At the same time, the population will become relatively older. A person born in 1967, when the population turned 200 million, could be expected to live 70.5 years. Life expectancy for those born today is 77.8 years.

The impact of the aging baby-boom generation, whose oldest members turn 60 this year, will be felt on Social Security and Medicare. "We really are doing very well in terms of extending life, and that is going to increase the rate of population growth," says Samuel Preston, a University of Pennsylvania demographer. It could also have political impact.

As the US moves toward 400 million people, Americans can be expected to marry later in life, and more of them will live alone. Between 1970 and 2005, the median age of first marriage moved from 23 to 27 for men and from 21 to 26 for women. Over the same period, the percentage of single-person households grew from 17 percent to 26 percent. Those trends are likely to continue.

Experts generally believe that expansion to meet the housing and other community needs of a growing population is likely to remain concentrated in suburbs and exurbs.

"Most projections show that the continued increase in the US population and the projected 50 percent increase in space devoted to the built environment by 2030 will largely take place in the sprawling cities of the South and West, areas dominated by low-density, automobile-dependent development of residential, commercial, and industrial space," writes demographic trend-watcher Joel Kotkin in a recent issue of the magazine The Next American City.

This kind of continuing development tied to US population growth worries many environmentalists, as well as those concerned about the loss of farmland.

Annual US population growth of nearly 3 million contributes to the water shortages that are a serious concern in the West and many areas in the East, says Lester Brown, president of the Earth Policy Institute. Water tables are now falling throughout most of the Great Plains and in the Southwest, he warns. Some lakes are disappearing and rivers are running dry.

"As water supplies tighten, the competition between farmers and cities intensifies," says Mr. Brown. "Scarcely a day goes by in the western United States without another farmer or an entire irrigation district selling their water rights to cities like Denver, Las Vegas, Phoenix, Los Angeles, or San Diego."

Concern about a growing populace and decreasing resources is likely to push governments toward conservation and more sustainable development, experts say.

This may be especially true of energy. Nineteen states and the District of Columbia now have renewable portfolio standards that require electric utilities to use more wind, solar, biomass, geothermal, and other renewable sources.

"The global context will really drive what happens in the United States," says futurist Hazel Henderson.

Last month, for example, the Chinese government released its first "green" gross domestic product (GDP) report. It measures economic growth while also factoring in the environmental consequences of that growth. Other governments and financial intuitions now are being pushed in the same direction. US portfolio managers in charge of $30 trillion in assets now demand carbon disclosures of all the companies in their portfolios, says Ms. Henderson.

"The tipping point has been reached there," says Henderson. "I feel very hopeful that the evolution to the solar age could happen much quicker than we might have expected because it's being driven by so many stress points, from global warming to water shortages to desertification."

By mid-century, she predicts: "Cars will be getting 100 m.p.g. if they're still using gasoline instead of fuel cells. That's definitely a no-brainer. Cities and towns will get more and more compact as these sprawling suburbs end up being too costly and inefficient."

That vision for the future contrasts sharply with Mr. Kotkin's. But given current political, economic, environmental, and social trends – especially the unknowns about world energy supplies – it is likely to be just as valid.

Meanwhile, the US population clock keeps ticking: Every 13 seconds somebody dies. Every 31 seconds there's another immigrant – legal or illegal. It adds up to a net gain of one person every 11 seconds, or about 8,000 every day. It took 39 years to add the most recent 100 million; the next 100 million will take a couple of years less than that.

The US population growth rate is expected to decline a bit by mid-century. Still, by then the numbers will have increased to some 420 million, according to official calculations. Critics of US immigration policy say the number could be significantly higher.

"If Congress should end up ducking the issue of immigration reform and maintaining the status quo of mass legal and illegal immigration, our population is projected to still continue its rapid growth," warns the Federation for American Immigration Reform in a recent report. "Our projection is for a population of between 445 and 462 million residents depending on the assumptions used."

But societal changes tied to population are more than numbers.

As the racial and ethnic mix among Americans shifts in the decades ahead, public attitudes are likely to change as well. In some ways, they already are.

For example, between 1986 and 2003, the share of adults who approved of interracial marriage rose from 70 percent to 83 percent, according to a Roper Reports study. This trend is especially true among young Americans. A 2002 Gallup survey showed that just 30 percent of adults 65 and older approved of marriage between blacks and whites. But among people between 18 and 29, 86 percent said they had no problem with interracial marriage.

"The fact that today we see young people intermarrying more, interracial dating much more common – all of that I think portends that we're going to become much more ecumenical in the way we look at things than we were in the past," says William Frey, a demographer at the University of Michigan and the Brookings Institution. "I think we'll have much more tolerance for people of other backgrounds, cultures and languages, points of view, and religious and belief systems."

What's certain is that there will be a lot more Americans.

• Last of five parts. Previous installments in this series appeared Sept. 12, 19, and 26, and Oct. 3.