Ehrlich slams 'big Australia' policy

An American ecologist has criticised a 'big Australia' policy, saying there are just not enough resources in a country already hit by climate change.

Stanford Professor Paul Ehrlich, who delivered the annual Jack Beal Lecture at the University of New South Wales in Sydney last night, spoke with SBS Presenter Anton Enus, as the world marks a population of seven billion.

"Australia is already over-populated... Look at the Murray-Darling situation. You are deforesting the country. You have got salinity problems in the wheat-lands of the west," he told SBS.

"The climate is changing and Australia is a major producer of greenhouse gases which threatens all future generations everywhere. So the idea that you should add more people to add to all of these problems is just plain-silly".

He said climate change is already impacting food production in a world were almost a billion people are hungry, and has called for world leaders to take urgent action.