Global debates about population policy are confusing. One side argues that rising human populations threaten our environment and prosperity. Land, water, energy, and biodiversity all seem to be under greater stress than ever, and population growth appears to be a major source of that stress.

The other side of the debate, mainly in rich countries, argues that households are now having so few children that there won't be enough to care for aging parents.

Those who fret about population growth have the better argument. Issues confronting Europe, Japan, and to a lesser extent the United States and some middle-income countries concerning aging populations are manageable. Moreover, the benefits of slower population growth outweigh the adjustment costs.

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