At the close of the 21st century, more than 11 billion people will inhabit this planet, according to the latest forecast from the United Nations’ population division. The forecast underlines President Obama’s assertion at the announcement of U.S. EPA’s Clean Power Plan: “We only get one home. We only get one planet. There’s no plan B.”

But while the number itself seems staggering, the real questions may lie in the unevenness of population growth: Where is the population growing the fastest? And which age groups will have the greatest population?

“Whether it is 10 billion or 11 billion, it is a big number and this has huge implications for food security, for resource management, for the environment,” said K. Bruce Newbold, director at the School of Geography and Earth Sciences at McMaster University in Canada. “I hate to be a doomsayer, but I do have concerns whether we are prepared for that.” Though population growth is slowing, the total world population itself is increasing, he said, and in areas that are already very vulnerable, like Africa.

This revision to previous U.N. forecasts incorporated new data from recent national surveys and demographic and health surveys. According to the revised estimates, India is set to overtake China six years earlier than previously predicted, but both countries face the specter of aging populations.

Climate change multiplies stress
China faces it more than India, because of China’s one-child policy, which brought fertility rates down significantly even as life expectancy continues to improve. While the two countries will continue to dominate the total population in terms of sheer numbers, Africa will see the sharpest increases in population, accounting for more than half of the global population growth over the next 35 years, said the report, which includes predictions for the years 2030, 2050 and 2100.

All of the 48 least-developed countries, of which 27 are in Africa, will witness steep population growth. Nigeria is expected to emerge as the third most populous country by 2050.

When you add the potential for climate change into that equation, it creates additional problems, Newbold said. Changes in precipitation patterns and possibly decreased precipitation in some parts of Africa, which will be unable to support crops and human habitation in the future, would have repercussions, said Roger-Mark De Souza, director of population, environmental security and resilience at the Woodrow Wilson International Center for Scholars. Even today, 20 million people in the Sahel region in Africa, which extends across the continent, are food insecure, he added.

The composition of the population will also play a crucial role in determining how countries deal with the stress posed by ballooning populations, experts noted. “Population is growing not just through childbearing but also because of longevity,” explained Sarah Harper, director at the Oxford Institute of Population Ageing at the University of Oxford.

Since the population growth is largely a result of better health outcomes, it means we will be adding to the ranks of vulnerable populations at both ends of the age spectrum—the very young and also the very old. The countries that will host these populations are already struggling to provide decent standards of living for their people.

The oldest of the old increase rapidly
The dramatic extension of life spans across the world, increasing from 70 years in 2010 to 2015 to 83 years in 2095 to 2100, may seem like unadulterated good news, but what that means for quality of life is not as straightforward.

The number of old people, above 60 years, will more than triple, increasing from 901 million in 2015 to 3.2 billion in 2100. The oldest of the old, above 80 years, are projected to increase at an even faster pace, their numbers increasing sevenfold by the turn of this century.

“When you look at changes in the environment and climate change impacts, those who are most vulnerable to those changes are the very young and the very old,” De Souza said. “This is true not just in places like Africa but across the world. We know that heat waves in Europe have led to the deaths of elderly people,” De Souza added. Europe currently hosts the highest proportion of elderly people in its population.

While it was beyond the scope of this report, analysis of population growth also takes into account how rapid urbanization would change the face of human settlements and affect their ability to adapt to climate change. In 2007, the United Nations predicted an explosion in urban populations, which it said could be as much as the three-quarters of the world population by 2050, mostly residing in developing countries.

China’s aging population and rapid migration to coastal urban centers will make the country more susceptible to effects of climate change like rising sea levels and extreme weather events, recent research by scientists at University College London and experts from the United States, China and India has found.

These predictions are important for adaptation because they help us plan ahead, De Souza said, and there is a need to understand population dynamics in the context of resilience.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500