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Atmospheric soot loadings from nuclear weapon detonation would cause disruptions to the Earth’s climate, limiting terrestrial and aquatic food production. Here, we use climate, crop and fishery models to estimate the impacts arising from six scenarios of stratospheric soot injection, predicting the total food calories available in each nation post-war after stored food is consumed. In quantifying impacts away from target areas, we demonstrate that soot injections larger than 5 Tg would lead to mass food shortages, and livestock and aquatic food production would be unable to compensate for reduced crop output, in almost all countries. Adaptation measures such as food waste reduction would have limited impact on increasing available calories. We estimate more than 2 billion people could die from nuclear war between India and Pakistan, and more than 5 billion could die from a war between the United States and Russia—underlining the importance of global cooperation in preventing nuclear war.

World Population Prospects 2022 is the twenty-seventh edition of the official United Nations population estimates and projections. It presents population estimates from 1950 to the present for 237 countries or areas, underpinned by analyses of historical demographic trends. This latest assessment considers the results of 1,758 national population censuses conducted between 1950 and 2022, as well as information from vital registration systems and from 2,890 nationally representative sample surveys. The 2022 revision also presents population projections to the year 2100 that reflect a range of plausible outcomes at the global, regional and national levels. For the first time, the estimates and projections are presented in one-year intervals of age and time instead of the five-year intervals used previously.

Le premier sommet mondial de la Terre, celui de Stockholm en 1972, avait déjà été consacré à des préoccupations majeures : comment vivre aussi nombreux sur une planète dont la démographie ne cesse de croître et une partie de ses ressources de décroître. Vingt ans plus tard, à Rio, ce sont pourtant les gaz à effet de serre et leur pouvoir de réchauffement, porteurs d’une problématique physique très différente, qui ont tenu le rôle principal. Et nous vivons aujourd’hui une étape nouvelle marquée par le caractère très largement irréversible des changements en cours.

Les facteurs démographiques à l’œuvre dans les évolutions entre 2002 et 2018. Le vieillissement démographique suscite des craintes budgétaires, notamment en matière de santé ; à cet égard il est utile de disposer de la structure des dépenses de santé par âge et, plus encore, de son évolution.