The world's population is expected to increase by 2 billion persons in the next 30 years, from 7.7 billion currently to 9.7 billion in 2050, according to a new United Nations report launched on Monday.

The World Population Prospects 2019: Highlights, which is published by the Population Division of the UN Department of Economic and Social Affairs, provides a comprehensive overview of global demographic patterns and prospects.

The study concluded that the world's population could reach its peak around the end of the current century, at a level of nearly 11 billion.

The report also confirmed that the world's population is growing older due to increasing life expectancy and falling fertility levels, and that the number of countries experiencing a reduction in population size is growing.

The resulting changes in the size, composition and distribution of the world's population have important consequences for achieving the Sustainable Development Goals (SDGs), the globally agreed targets for improving economic prosperity and social well-being while protecting the environment.

The new population projections indicate that nine countries will make up more than half the projected growth of the global population between now and 2050: India, Nigeria, Pakistan, the Democratic Republic of the Congo, Ethiopia, the United Republic of Tanzania, Indonesia, Egypt and the United States of America (in descending order of the expected increase).

Around 2027, India is projected to overtake China as the world's most populous country.

The population of sub-Saharan Africa is projected to double by 2050 (99% increase).

Regions that may experience lower rates of population growth between 2019 and 2050 include Oceania excluding Australia/New Zealand (56%), Northern Africa and Western Asia (46%), Australia/New Zealand (28%), Central and Southern Asia (25%), Latin America and the Caribbean (18%), Eastern and South-Eastern Asia (3%), and Europe and Northern America (2%).

The global fertility rate, which fell from 3.2 births per woman in 1990 to 2.5 in 2019, is projected to decline further to 2.2 in 2050.

A fertility level of 2.1 births per woman is needed to ensure replacement of generations and avoid population decline over the long run in the absence of immigration.

Liu Zhenmin, United Nations Under-Secretary-General for Economic and Social Affairs, said the report offers a roadmap indicating where to target action and interventions.

"Many of the fastest growing populations are in the poorest countries, where population growth brings additional challenges in the effort to eradicate poverty, achieve greater equality, combat hunger and malnutrition and strengthen the coverage and quality of health and education systems to ensure that no one is left behind."

People in the poorest countries still live 7 years less than the global average

Life expectancy at birth for the world, which increased from 64.2 years in 1990 to 72.6 years in 2019, is expected to increase further to 77.1 years in 2050.

While considerable progress has been made in closing the longevity differential between countries, large gaps remain.

In 2019, life expectancy at birth in the least developed countries lags 7.4 years behind the global average, due largely to persistently high levels of child and maternal mortality, as well as violence, conflict and the continuing impact of the HIV epidemic.

By 2050, one in six people in the world will be over age 65 (16%), up from one in 11 in 2019 (9%).

Regions where the share of the population aged 65 years or over is projected to double between2019 and 2050 include Northern Africa and Western Asia, Central and Southern Asia, Eastern and South-Eastern Asia, and Latin America and the Caribbean.

By 2050, one in four persons living in Europe and Northern America could be aged 65 or over. In 2018, for the first time in history, persons aged 65 or above outnumbered children under five years of age globally.

The number of persons aged 80 years or over is projected to triple, from 143 million in 2019 to 426 million in 2050.

The potential support ratio, which compares numbers of persons at working ages to those over age 65, is falling around the world.

In Japan this ratio is 1.8, the lowest in the world.

An additional 29 countries, mostly in Europe and the Caribbean, already have potential support ratios below three.

By 2050, 48 countries, mostly in Europe, Northern America, and Eastern and South-Eastern Asia, are expected to have potential support ratios below two.

Since 2010, 27 countries or areas have experienced a reduction of one per cent or more in the size of their populations.

This drop is caused by sustained low levels of fertility.

The impact of low fertility on population size is reinforced in some locations by high rates of emigration. Between 2019 and 2050, populations are projected to decrease by one per cent or more in 55 countries or areas, of which 26 may see a reduction of at least ten per cent.

In China, for example, the population is projected to decrease by 31.4 million, or around 2.2 per cent, between 2019 and 2050.

Between 2010 and 2020, fourteen countries or areas will see a net inflow of more than one million migrants, while ten countries will see a net outflow of similar magnitude.

Some of the largest migratory outflows are driven by the demand for migrant workers (Bangladesh, Nepal and the Philippines) or by violence, insecurity and armed conflict (Myanmar, Syria and Venezuela).

Belarus, Estonia, Germany, Hungary, Italy, Japan, the Russian Federation, Serbia and Ukraine will experience a net inflow of migrants over the decade, helping to offset population losses caused by an excess of deaths over births.

The report includes updated population estimates from 1950 to the present for 235 countries or areas, based on detailed analyses of all available information about the relevant historical demographic trends.

The latest assessment uses the results of 1,690 national population censuses conducted between 1950 and 2018, as well as information from vital registration systems and from 2,700 nationally representative sample surveys.

The 2019 revision also presents population projections from the present until 2100, depicting a range of possible or plausible outcomes at the global, regional and country levels.