What is the concept of a 'demographic winter'? Is the world moving towards such a situation? Elaborate.

The concept

Replacement total fertility is about 2.1 children per woman in low-mortality societies. Below that for decades, each generation is smaller. Median age rises. The share of people above 65 grows. The potential support ratio of workers to retirees falls. The idea also implies social effects: fewer siblings, delayed marriage, empty schools, immigration as a labour fix, and anxiety about decline. East Asia and much of Europe are the textbook cases: Japan, South Korea, Italy, Spain, Germany. Some governments pay baby bonuses. None has found a simple switch.

The concept is regional. A country can have below-replacement fertility and still grow for a time because of population momentum and immigration.

• Below-replacement fertility: This is the engine of the idea.
• Ageing and shrinkage: First the pyramid greys. Then absolute numbers may fall.
• Political economy: Pensions, health, and who does care work become the central state problem.

Is the world moving there?

Globally, fertility has fallen sharply from the mid-twentieth century. UN population projections show a world that grows more slowly and ages, with a peak later this century in many central scenarios. That is a move toward winter in the average. It is not an arrival. Sub-Saharan Africa still has high fertility and will supply much of future world population growth. South Asia is mixed. India’s fertility has fallen to around replacement in recent National Family Health Survey rounds, with large State variation. Latin America and East Asia are already in or near winter. The world is therefore diverging. There is a grey North and East Asia, a still-young Africa, and a middle belt.

Migration can postpone winter in receiving countries. It does not raise the world’s birth rate. Climate, housing costs, women’s education and the unfinished gender contract of care are the real drivers of low fertility. There is not a single cultural death.

• Yes, in structure: Global ageing and sub-replacement fertility appear in a rising share of countries.
• No, as a uniform fate: Africa’s youth and momentum keep world population from a sudden freeze.
• India’s place: India has a closing window of dividend. It is not yet a Japanese-style winter. Some States already look East Asian.

Demographic winter is a fair warning for rich low-fertility societies. It is a bad map if it erases the child-rich parts of the world that still need schools more than geriatric wards.