What will the impact be?
Without migration, countries will face ageing and shrinking populations.
Dr George Leeson, director of the Oxford Institute of Population Ageing, says that does not have to be a bad thing, as long as the whole of society adjusts to the massive demographic change.
He told the BBC: “Demography impacts on every single aspect of our lives, just look out of your window at the people on the streets, the houses, the traffic, the consumption, it is all driven by demography.”
“Everything we plan for is not just driven by the numbers in the population, but also the age structure and that is changing, so fundamentally we haven’t got our heads around it.”
He thinks workplaces are going to have to change and even the idea of retiring at 68, the current maximum in the UK, will be unsustainable.
The report, part of the Global Burden of Diseases analysis, says affected countries will need to consider increasing immigration, which can create its own problems, or introducing policies to encourage women to have more children, which often fail.
Report author Prof Murray argues: “On current trends there will be very few children and lots of people over the age of 65 and that’s very difficult to sustain global society.”
“Think of all the profound social and economic consequences of a society structured like that with more grandparents than grandchildren.”
“I think Japan is very aware of this, they’re facing declining populations, but I don’t think it’s hit many countries in the West, because low fertility has been compensated with migration.”
“But at a global level there is no migration solution.”
But while the change may challenge societies, it may also have environmental benefits given the impact of our species.