Shinzo Abe, Japan's prime minister, in Vladivostok, Russia, on Sept. 5. (Andrey Rudakov/Bloomberg)

Francisco Toro, in his Sept. 1 op-ed, “Japan is a Trumpian paradise — and a dying country,” painted a grim picture of Japan’s declining population, but there is a different picture worth considering. If one makes an effort to calculate the “optimum population” for Japan given its natural-resource endowment and the likely impact of global warming over the next century, a number well below the current 127 million could be the answer. It could be about 90 million, roughly the size of Japan’s population in 1960. Mr. Toro was wrong to assume that Japan’s fertility rate will remain below the 2.1 replacement level forever. The key to stabilizing Japan’s population at some optimum level will be addressing a point he makes: Japan is “one of the least attractive places for women to have children.”

Contrary to what Mr. Toro wrote, Japan can get by without migrants. What it needs is policies that make most women want to have two or more children. As work and home lives evolve in the face of robotics and artificial intelligence, these policies can come naturally and gradually. They don’t need to be draconian. Japanese women will also be more inclined to start families when they see global population stabilizing, or even declining, which will lead to a safer world for their children, their grandchildren and future generations.

Lex Rieffel, Washington

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