By Doug Struck

| GLOBE CORRESPONDENT   MAY 02, 2014

Environmental apostles are only too ready to tell us what is wrong with society. But they go mum over the subject of people — specifically, too many people.

One need not drill very far into any given assault on the environment to find an explanation in the world’s hurtling population. The “hockey stick” graph showing the exponential rise in greenhouse gases — the Holy Grail of climate change scenarios — mirrors the graph of the increase in human population.

That is no coincidence.

Our planetary presence was fairly small for 200,000 years, inched toward 2 billion by 1930, and then rocketed skyward. It is now at about 7.3 billion, and expected to rise to 10 billion, give or take a billion, just after mid-century. We are growing, noted author Alan Weisman, at the clip of a million people every 4½ days — tripling or quadrupling our numbers just in the course of one lifetime.

In doing so, we are fouling the atmosphere with greenhouse gases, poisoning the land with chemicals, turning our seas into acid and emptying them of fish, sucking up water and other resources far faster than they can be replenished.

Yet environmentalists have been loath to say the obvious: The world needs to stop having so many babies.

“They don’t want to touch this. It’s very explosive, very sensitive,” said Weisman, who appeared on a panel this week at the Boston Center for the Arts to talk about population. “The idea of not reproducing feels somehow unnatural,” he noted. “And then there is religion.”

Weisman has given a lot of thought about the end-game of the population explosion. He wrote “The World Without Us,” a sobering description of how quickly the traces of mankind would be swallowed by nature if we ceased to exist. (He did not specify the cause of our demise; the suspects make a lengthy list.) Now Weisman has written “Countdown: Our Last, Best Hope for a Future on Earth?” a prescription for a planet-friendly and smaller population gotten there through birth control, education, and equality for women.

He appeared on the panel as part of a series of talks on “The Future of Nature,” sponsored by The Nature Conservancy.

Preaching for a smaller population leads immediately to the question of who is not supposed to have babies, and that quickly gets into electrified topics of class, culture, affluence, and racism, noted another panelist, Roger-Mark De Souza, a population expert with the Wilson Center.

“There is a history around population issues that is associated with eugenics, with population control programs, with forced sterilization,” he noted. “It brings up questions of abortion, of immigration, of youth sexuality. A lot of environmental organizations say, Why should conservation organizations deal with this? It’s too far from our mission. You have to be very careful.”

But Caroline Crosbie, of Pathfinder International, a reproductive rights group, said the aversion to advocacy of birth control is easing, as education levels increase and strictures relax. “There’s been a change in most developing countries. The US is going in the reverse direction,” she said.

Most religions have some version of “go forth and multiply” among their tenets. But many religions are recognizing the reality of the need for reproductive limits, and even the Catholic Church’s “rhythm method” of birth control is a grudging nod in that direction, said Crosbie.

But the real question for environmentalists — and for society — is how many people are enough people for the earth. Scientists pose the question as the “carrying capacity” of the planet — a vaguely technical term that suggests the answer is a simple matter of calculating the finite resources of earth and determining if we will run out.

Of course we will run out, but the calculation is not so simple. When Paul and Anne Ehrlich’s “The Population Bomb” was published in 1968, society was alarmed by their prediction of massive starvation in the 1970s because, they said, the planet could not possibly support too many more than the 3.5 billion people who lived when the book was published.

But we barreled through that limit at high speed, thanks largely to a “green revolution” of greatly accelerated agricultural production on the back of fossil fuel-based fertilizers. Many feel we have now reached the practical limits of that revolution, and some believe that food made through genetically modified organisms will give us our next burst of nutrition at a yet-unknown risk to other biology.

In truth, most estimates say we already have far exceeded the carrying capacity of the earth, and we are borrowing from mankind’s future. But how much are we borrowing, and how soon will that debt come due? “The correct number,” Weisman noted, “is not one anybody can know for sure.”

Doug Struck, a journalist for 35 years, reports on environmental matters from Boston. He can be reached at doug@dougstruck.com.