PARIS — In 2040/2050, will demographers speak of "the white man's loneliness" in the way historians once referred to "the white man's burden" to describe the so-called "imperial responsibilities" of some European nations?

Demography is not an exact science. Countless dire predictions, from that of Malthus to that of the Club of Rome, have been proven wrong. But, according to a recent and very convincing essay published in the magazine Foreign Affairs, a dual demographic and economic trend is taking place that will result in spectacular shifts by the middle of this century. The Western world will represent only 12 percent of the world's population, with Europeans reduced to 6 percent. (In 1913, a year before the outbreak of World War I, Europe was slightly more populated than China.)

Economically, the West will account for around 30 percent of global output — a level that corresponds to Europe's share in the 18th century and down from 68 percent in 1950.