THE WAR AGAINST GLOBAL warming is producing collateral damage to family life. One American city may even ban the hearth--San Francisco is contemplating a prohibition on private fireplaces to reduce air pollution. But this is nothing compared to the family sacrifice of the future: babies.

A new trend among some of the world's most eco-conscious is to forgo children for the sake of the planet. In a recent interview with Britain's Daily Mail, one woman who works for an environmental charity told of aborting her baby because she felt it was "immoral to give birth to a child that . . . would only be a burden to the world." She also had herself permanently sterilized at age 27 for good measure. According to another woman, who works for Ethical Consumer magazine, sterilization was the most ethical decision because " . . . a baby would pollute the planet--and that never having a child was the most environmentally friendly thing I could do."

Whether you view these women as courageous or completely unbalanced, they certainly are self-sacrificing in relinquishing the personal joys of parenthood for the good of the earth, right? Wrong. The truth about children is that they don't make most parents happier, and they don't create a net drain on the world. According to the evidence, forgoing kids is hardly a selfless act.

Many sources of data show that kids lower the self-perceived happiness of parents, on average. For example, the 2004 General Social Survey shows that, if two adults in 2004 were the same in age, sex, income, marital status, education, race, religion, and politics--but one had kids but the other did not--the parent would be about seven percentage points less likely than the non-parent to report being "very happy."

Furthermore, the average happiness of adults--correcting for all the other personal characteristics like before--falls as more kids are added to the family. This is true, however, only up to four kids--with the fifth, parental happiness appears to start to rise again. The reason for this is because, in modern America where the average number of children per family is close to two, a large brood generally belongs to a certain unusual type of heroic parent (who fall into the category of saints and martyrs).

These facts should not be interpreted as evidence that non-parents are, as a group, happier people than parents. People who have the most kids today generally have other traits that more than offset the children in their happiness. For example, political conservatives have far more children than liberals (41 percent more kids per couple in 2004), but their worldview brings them up more than their kids bring them down: 42 percent of conservative parents are very happy, versus 21 percent of liberal non-parents. (In case you're wondering, 52 percent of conservative non-parents are very happy.)

The main reason that kids dent their parents' bliss appears to be the effect children have on marriage. Multiple studies show that the quality of a marriage, which is critically important for life satisfaction, falls precipitously after the birth of a couple's first child. The nadir for a marriage is--no surprise--when the children are adolescents. On the bright side, marriages tend to get better quickly after this point, and reach their happiest levels after the kids move out.

What about the assertion that kids--whether they make you happy or not--are a net burden on our world? It turns out that this does not stand up to the evidence either. Economists estimate that the net benefits to society from children are, on average, significant and positive. Balancing the negative and positive socioeconomic impacts from children, one well-regarded study from 1990 in the Annals of the American Academy of Political and Social Science placed the benefit in net government revenues in excess of $100,000 per American child--a number that has obviously greatly increased since that time.

What we choose to do with this public surplus per child is obviously up to us--it reflects our society's values. As our population rises, we can use our resulting public wealth increases to ensure the preservation of our natural environment, for example. To argue against human reproduction to save the planet amounts to arguing that lowering our prosperity is the best strategy to cut resource consumption and greenhouse gases. A common complaint about the current environmental movement is that it cares more about trees than people. This complaint is certainly not weakened by arguments for negative population growth.

Some have concluded that the decision to forgo children--increasingly common in Europe and some parts of American society--is not a benevolent decision for humanity at all, but rather a reflection of endemic modern selfishness. In addressing the problem of negative population growth in Germany, none other than the head of that country's left-wing Social Democratic Party said in an interview that, "Living for the moment does not help a society develop itself. . . . A society without children is a society without a future."

W.C. Fields was once asked, "Do you like children?" to which Fields replied, "I do if they're properly cooked." Such disdain for children is amusing, but it is hardly a display of humanitarian bona fides.

Arthur C. Brooks, a professor at Syracuse University's Maxwell School and a visiting scholar at the American Enterprise Institute, is the author of the just-published Gross National Happiness (Basic Books).

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