When the world meets in New York next month to adopt a bold new vision for sustainable development, a key area of concern will be the globe’s burgeoning population, which is projected to reach 8.5 billion people by 2030 and 9.7 billion in 2050, from 7.3 billion people currently.

A new UN report, World Population Prospects: The 2015 Revision, notes that about half of this growth will be experienced in Africa, which, notably, has the highest rate of population growth already. High population growth rates present their own set of challenges.

This should worry world leaders because the final scorecard on the Millennium Development Goals, released recently, notes that the continent lags behind the other developing regions on most targets.

Even though the UN said remarkable gains have been made worldwide on the eight MDGs, its overall verdict is that “progress has been uneven across regions and countries, leaving significant gaps.”

This “unevenness” is among the setbacks that world leaders would be keen to overcome if the Sustainable Development Goals which take effect from January next year, are to be rated as successful.

“Understanding the demographic changes that are likely to unfold over the coming years, as well as the challenges and opportunities that they present for achieving sustainable development, is key to the design and implementation of the new development agenda,” said Wu Hongbo, UN Under-Secretary-General for Economic and Social Affairs.

In particular, the new UN report notes that the populations of 28 African countries are projected to more than double by 2050, and by 2100, 10 African countries including Uganda, Burundi and Tanzania are projected to increase by at least a factor of five. The others are Angola, the Democratic Republic of Congo, Malawi, Mali, Niger, Somalia and Zambia.

In fact, Tanzania and Uganda make it to the list of nine countries worldwide in which half of the world’s population growth is expected to be concentrated. The two countries take position six and nine respectively, in the size of their contribution to the total growth.

The first is India, then Nigeria, Pakistan, DRC and Ethiopia in that order. In seventh position is the US, followed by Indonesia.

Most of the projected increase in the world’s population is attributed to a short list of high fertility countries mainly in Africa, or those with already large populations.

“The concentration of population growth in the poorest countries presents its own set of challenges, making it more difficult to eradicate poverty and inequality, to combat hunger and malnutrition, and to expand educational enrolment and health systems, all of which are crucial to the success of the new sustainable development agenda,” said John Wilmoth, director of the population division in the UN’s Department of Economic and Social Affairs.

Africa is expected to play a central role in shaping the size and distribution of the world’s population over the coming decades because it has a large number of young people who will reach adulthood in the near future and who will start having children of their own.

But on the flip side, a young population is a positive thing because it creates an opportunity for countries to capture a demographic dividend.

In Africa, children under the age of 15 account for 41 per cent of the population and young persons aged 15 to 24 account for a further 19 per cent, UN estimates show.