Source: Estimates and UN Population Division: World Population Prospects: The 2012 Revision, online
The UN has developed three population projections, called variants – one high, one low, and one in between. Of these, the medium variant suggests that the world population will grow to about 10 billion by the middle of this century, and will level off at about 11 billion by the end of it. However, if fertility declines by less than assumed, the world population could grow to about 17 billion by the end of the century. If fertility falls by more than assumed, the world population could slightly fall over current levels to about 7 billion.
The UN publishes its population projections every two years, and over the past decades, the medium variant of the projections has often been corrected upward, meaning the population has grown more quickly than expected. The most recent upward correction was due to a slower fertility decline than anticipated in countries in sub-Saharan Africa and South Asia, as well as higher-than-expected levels of fertility in large and populous countries of Asia.
The recent past has seen enormous changes in fertility rates and life expectancy. In the early 1970s, women had on average 4.5 children each; by 2014, total fertility for the world had fallen to around 2.5 children per woman. Meanwhile, average global lifespans have risen, from 64.8 years in the early 1990s to 70.0 years today.
In addition, the world is seeing high levels of urbanization and accelerating migration. 2007 was the first year in which more people lived in urban areas than in rural areas, and by 2050 about 66 per cent of the world population will be living in cities.
These megatrends have far-reaching implications. They affect economic development, employment, income distribution, poverty and social protections. They also affect efforts to ensure universal access to health care, education, housing, sanitation, water, food and energy. To more sustainably address the needs of individuals, policymakers must understand how many people are living on the planet, where they are, how old they are, and how many people will come after them.
Why is the population growing so quickly?
The huge growth in the world population over the past two centuries is largely the result of advances in modern medicines and improvements in living standards. These have significantly reduced infant, child and maternal mortality, contributing to an increase in life expectancy. Although fertility levels have declined, they have not fallen at the same pace as mortality levels.
The world population will continue to grow for decades to come. This is the result of ‘population momentum’: Because of improved survival rates and past high fertility levels, there are more women of reproductive age today. This will contribute to a relatively large number of births, even if those women have fewer children on average. Although population growth is, today, largely attributable to population momentum, after 2060 it will almost exclusively be driven by fertility levels in the world’s least developed countries.
A varied landscape
General population trends mask considerable differences between countries. On the one side stand the world’s least developed countries, which continue to have high fertility levels. According to conservative projections, the population of the world’s least developed countries will double by 2050, and in some countries it will even triple. On the other side are high-income and rising-income countries, which are experiencing slow population growth or no population growth at all. Whereas the former continue to have large, growing, populations of young people, the latter have large, growing populations of older persons. (There are some countries experiencing a decline in population size. However, in most cases this is not only the result of low fertility, but also the result of high mortality and emigration due to weak and deteriorating economic, social and political conditions.)
While demographics vary considerably at national levels, the overall trends have global implications for sustainable development. The global climate will change no matter where greenhouse gases are emitted, for example. Efforts to sustainably meet the needs and desires of a growing world population will have implications for all countries – as will failure to meet these needs.
While surges in population will bring challenges, they also represent humanity's success. The move from higher to lower mortality and fertility reflects achievements in health, education and human rights. Falling fertility levels also create opportunities for countries to realize a demographic dividend – the economic growth that can occur when there is an increase in the number of people of working age and a decrease in the number of dependents.
Population dynamics can be shaped by policies. But these policies must strengthen, rather than weaken, fundamental human rights and freedoms. Population dynamics are the cumulative result of individual choices and opportunities, and they are best addressed by enlarging these choices and opportunities – especially those related to sexual and reproductive health and rights. When couples can freely decide the number, timing and spacing of their children, evidence shows more children survive and thrive, and overall fertility levels trend downward.
Sexual and reproductive health and rights also make an enormous difference in the health and lives of all people, especially women, by dramatically reducing maternal and infant mortality rates, helping to prevent the spread of communicable diseases such as HIV, and empowering women to live more self-determined lives.
What UNFPA is doing?
UNFPA is one of the world’s largest supporters of population data collection. In addition to supporting censuses and surveys, UNFPA works with policymakers, civil society, health-care providers and educators at all levels to promote sexual and reproductive health and rights – including voluntary family planning.