“Population Explosion” was a call to arms for American environmentalists 40 years ago, amid fears that baby boomers would have big families. That didn’t happen, but hyper-population-growth is occurring now due to large-scale immigration.

California has just projected a population of 60 million by mid-century, up 5 million from its forecast of only three years ago. We’re talking about a 75 percent leap between 2000 and 2050 – by any measure, a population explosion.

That’s the truth, but one that has sent many environmental leaders into hiding. Most of California’s population growth will come from immigrants and their relatively high birthrates, but the Sierra Club refuses to touch the matter. Once a tiger on U.S. population growth, it has retreated behind calls for a global approach that, it contends, will reduce the demands to immigrate to the United States.

Problem. Despite great strides in reducing birthrates in many poor countries – Mexico is one of the success stories – the world’s population is still expected to jump to 9 billion from 6 billion by 2050. Mass immigration to the United States, if anything, eases the pressure on other governments to promote family planning.

Not a few Sierra Club members have challenged the group’s spineless response to a spiraling American population. Prominent among them is Dick Lamm, the former Democratic governor of Colorado.

“I can’t believe my friends who are still jerking their knees out of the ’60s,” says the always outspoken Lamm. “It’s really important to be sensitive, but I can’t understand the fact that we are not talking about issues that are fundamental to America’s future.”

Overpopulation isn’t the only environmental threat, Lamm concedes, “But if you pass every item on the Sierra Club’s agenda, yet you have a billion Americans at the end of the century, it’s a Pyrrhic victory (a gain offset by staggering losses).”

The prospect of 25 million more Californians in a mere 40 years – and the added cars, shopping malls, sprawling developments and lost species that implies – alarms a splinter group called Sierrans for U.S. Population Stabilization (www.susps.org).

“With that kind of overpopulation, California is going to be importing virtually all the resources needed to sustain ourselves,” warns the faction’s co-chairman, Dick Schneider.

A consultant on citizens’ growth-control ballot measures, Schneider says that California cities and towns will be pretty much on their own. Some may try to set zoning that balances their goals for open space, quality of life and projections for growth. That will require fighting off the real-estate developers who often dominate local governments and accepting a loss of state money.

Demographers say that the population boom could be slowed if Californians refuse to build the roads and other infrastructure needed to accommodate the surge. The resulting congestion would stall the economy – attracting fewer people and prompting more Californians to relocate. This emigration, already well underway, would export California’s population pressures to Arizona, Colorado, Oregon, Washington and other Western states.

This is what passes for population policy in the United States: Make people so miserable that they leave.

There have been glimmers of liberal courage. In 1996, President Clinton’s Council on Sustainable Development called for a halt in population growth, citing mass immigration as a main driver. While noting the delicacy of the issue, the group forthrightly recommended, “Priority attention should be given to implement and enforce national policies on illegal and legal immigration.”

Population concerns took a back seat during the recent struggle over immigration reform. But because the bill would have vastly accelerated the numbers of legal entrants, its defeat ended up serving the cause.

It really is time for a national population policy – an honest one.

Froma Harrop is a Providence Journal columnist. Contact her by writing to fharrop@projo.com.