The number of human beings on the planet is expected to shoot past the 7 billion mark later this year, 2011, up from 6 billion in 1999. The growth is so rapid, that global population has doubled between 1960 and 2000, and a further increase of 2 to 4.5 billion is projected for the current half-century, mostly in least developed nations. Writing in a review article published today, 29 July, in Science, professor David Bloom of the Harvard School of Public Health (HSPH) suggests these huge increases herald the biggest global demographic upheaval in human history.

During 2011, we can expect births to reach 135 million and deaths to total 57 million, leaving a net increase of 78 million, about the same as the population of Europe in 1600 (excluding Russia and the Ottoman Empire).

The main cause of the rapid growth we have seen so far is that deaths have fallen dramatically, and although fertility has also dropped, that is women are having fewer children, it lags behind the fall in deaths.

New figures from the United Nations also suggest that by 2100, there will be 10.1 billion of us, although this could vary from as low as 6.2 to as high as 15.8 billion, depending on whether the number of births per woman continues to fall, and if so, how fast.

Less developed nations will face big challenges, where 97% of the 2.3 billion population growth is expected to take place. Nearly half of this (49%) will be in Africa.

This will be in stark contrast to what is expected to happen in more developed nations, whose populations are unlikely to grow, but will have an aging profile, with fewer people of working age supporting older adults living on pensions.

Bloom, who is Clarence James Gamble Professor of Economics and Demography at the HSPH, writes that although the problems of rich and poor countries will be different, because we live in a globalized world “demographic challenges anywhere are demographic challenges everywhere”.

Many developing nations are already straining to meet their people’s needs for food, water, housing and energy. These difficulties will increase, with knock-on effects being felt in other areas like health, economic growth and security.

In the past, despite “alarmist predictions, historical increases in population have not been economically catastrophic,” writes Bloom, and:

“Moreover, changes in population age structure have opened the door to increased prosperity.”

He sees that the demographic shift that we are facing is complex and poses huge challenges, but these are not insurmountable, and we should not just stick our heads in the sand and hope for the best: we have work to do.

“We have to tackle some tough issues ranging from the unmet need for contraception among hundreds of millions of women and the huge knowledge-action gaps we see in the area of child survival, to the reform of retirement policy and the development of global immigration policy,” writes Bloom.

“It’s just plain irresponsible to sit by idly while humankind experiences full force the perils of demographic change,” he urges.

Written by: Catharine Paddock, PhD