Couples who have more than two children are being "irresponsible" by creating an unbearable burden on the environment, the British government's green adviser warned.
Jonathon Porritt, who chairs the government's Sustainable Development Commission, says curbing population growth through contraception and abortion must be at the heart of policies to fight global warming.
He says political leaders and green campaigners should stop dodging the issue of environmental harm caused by an expanding population.
A report by the commission, to be published next month, will say that governments must reduce population growth through better family planning.
"I am unapologetic about asking people to connect up their own responsibility for their total environmental footprint and how they decide to procreate and how many children they think are appropriate," Porritt said.