One camp, led by Malcolm Turnbull, accepts that humans are causing climate change, and wants rapid action to change that. A second, led by Nick Minchin and Tony Abbott, rejects the mainstream science on global warming and the need to do anything.

Between them is a third group, which is more uncertain what to believe or do. It wants to put off a decision until after next month's summit in Copenhagen shows what the rest of the world will do.

To many Australians, that makes sense. Australia emits just 1.5 per cent of the world's greenhouse gas emissions. Whatever we do won't stop global warming. Shouldn't we wait to know what others will do before we decide what to do ourselves?

Some say this is where Joe Hockey would take the Liberals if he becomes leader. That would buy him time, but in reality, waiting for Copenhagen doesn't make sense.

First, Copenhagen is essentially about setting broad targets for future emissions, and some global issues, such as who will pay to bring low-emissions technology to developing countries.

The emissions trading debate, by contrast, is about the detailed design of how Australia's scheme would operate. The Copenhagen talks will have little bearing on that. They might produce a statement of principles, and a list of countries' targets, but not a detailed set of rules.

Second, we know what our targets will be, and what those of the key players will be. The world's largest economy, the European Union, decided long ago that by 2020, it would cut its emissions at least 20 per cent below 1990 levels. In Australia, Labor and Liberals agreed long ago to aim to cut emissions in 2020 to 5 per cent below year 2000 levels.

On Wednesday, the White House said the US would target cuts by 17 per cent from 2005 levels by 2020, rising steeply to a 42 per cent cut by 2030. A day later, China pledged that by 2020, it would cut carbon emissions per unit of GDP by 40 to 45 per cent from 2005 levels.