Advocates of curbing population growth as a means of reining in Australia's greenhouse emissions ought to be careful what they wish for. They might indeed reduce our emissions, but at significant economic cost, when Australia has already embarked on a process to reduce emissions growth in a way that will have minimal impact on economic growth.

First, yes, our relatively high population growth, both by birth and immigration, is a key driver of Australian emissions growth. And as anti-migration pundit Bob Birrell argued in 2009, high population growth cancels out the ongoing emissions-reduction benefits of energy efficiency. Moreover, immigration to Australia is a net addition to global emissions. Outside oil sheikdoms, Australia has more or less the highest emissions per capita in the world. Anyone who migrates here, unless they're coming from the US or Canada, is likely to significantly lift their net emissions, especially if they came from a less developed country. The more people who become Australians, the higher global emissions, all things being equal.