World population prospects: the 2002 revision
Population estimates and projections suggest that for the first time, future fertility levels in most developing countries will likely fall below 2.1 children per woman, the level needed to ensure the long-term replacement of the population, at some point in the twenty-first century. By 2050, the medium variant of the 2002 Revision projects that three out of every four countries in the less developed regions will be experiencing below-replacement fertility.
The 2002 Revision indicates a worsening of the impact of the HIV/AIDS epidemic in terms of increased morbidity, mortality and population loss. Although the probability of being infected by HIV is assumed to decline significantly in the future (particularly after 2010), the long-term impact of the epidemic remains dire.
As world fertility continues to decline and life expectancy rises, the population of the world will age faster in the next 50 years than during the past half century. An increase in the median age - the age that divides the population into two equal halves - is used as an indicator of the shift of the population age distribution towards older ages. Over the past half century, the median age for the world increased by 2.8 years, to 26.4 years in 2000. Over the next 50 years, the median age is expected to rise by 10.4 years, reaching 36.8 years in 2050.
The more developed regions have been leading the process of population ageing. The median age in these areas is projected to reach the unprecedented level of 45.2 years in 2050. But it is predicted that a more rapid period of ageing lies ahead for less developed regions in the next fifty years.
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