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.