The global population is about to reach eight billion — and by 2050 one billion people may be refugees because of the climate crisis.
The population figure is likely to be hit on Tuesday during the Cop27 summit.
United Nations Secretary General Antonio Guterrres said: “This milestone puts into perspective what this climate conference is all about.
"How will we answer when Baby 8 Billion is old enough to ask, ‘What did you do for our world – and for our planet – when you had the chance?’
“This UN Climate Conference is a reminder that the answer is in our hands. And the clock is ticking.”
The UN estimates the world’s population may grow to 8.5 billion in 2030 and 9.7 billion in 2050 and peak at 10.4 billion in the 2080s.
The rate of population growth varies hugely across the world.
The highest is in 10 African countries, with South Sudan topping the list at 5.5%. In the UK, it is just 0.53%. Next year India is expected to pass China as the world’s most populous country.
Barbados Prime Minister Mia Mottley warned: “We need to have a different approach. Unless that happens, we are going to see an increase in climate refugees.
“By 2050, the world’s 21 million climate refugees today will become one billion. We were the ones whose blood, sweat and tears financed the industrial revolution.
“Are we now to face double jeopardy by having to pay the cost due to those greenhouse gases from the industrial revolution? That is fundamentally unfair.”
Mr Guterres hit out at fossil fuel firms with net zero vows who are still expanding their operations.
He said: “Net zero commitments have varying levels of rigour and loopholes wide enough to drive a diesel truck through. We must have zero tolerance for net zero greenwashing.”