Once again Kevin Rudd is facing a Big Test; only this time the examination paper has been designed not by the pompous zealots of the Murdoch Press, but by professor Ross Garnaut.

Garnaut’s interim report on the economics of climate change is couched in vivid and passionate language about the threat to the Barrier Reef, the snowfields and the Murray Darling: but it can be expressed in drier terms.

People are essentially small and temporary carbon sinks which consume other small carbon sinks (food) and emit carbon dioxide. The problem comes when, to fulfil their needs and desires, they unlock the big carbon sinks, the fossil fuels: coal, oil and gas. The emissions these produce alters the environment.

The earth itself is not under threat but we have now reached the point where it will become markedly less comfortable for a number of life forms, including humans. The science is conclusive: only the stupid and perverse reject it. Thus it makes sense to cease producing these emissions, or at least find a way of controlling them.

Which leads to Garnaut’s multiple-choice question: Should we (a) take drastic action which will produce a decisive result or (b) take some action to at least ameliorate the problem or (c) do nothing and prepare for disaster?

I suspect Rudd’s instinctive response would be to go for (a), but, as last week’s COAG meeting showed, politics isn’t always as simple as that. Faced with an immediate and probably irreversible threat to the Murray-Darling Basin, Rudd and the Premiers opted not for urgent action, but to set up an organisation to decide what action to take next year. This is not a good sign when facing the far more complex and potentially painful response to climate change.

And of course, the opposition is already mounting up. Brendan Nelson has made it clear he wants to push back Rudd’s deadline for a carbon trading scheme beyond 2010, and even then he wouldn’t support it if it involved an increase in petrol prices. Anyone who didn’t think $1.70 a litre was sending a sufficient price signal must live on another planet. This other planet, presumably, is called “Europe,” where the price had been higher than that for years, but Nelson has never been big on geography. The New South Wales Labor government wants compensation for its electricity plants. The manufacturing unions want protection for their members.

Garnaut has insisted that for the scheme to be effective, transport (which means petrol) must be included and compensation should be limited to export industries and to low income earners: the rest should pay up and shut up. But Rudd is already backing away from such economic purity. Garnaut, who a year ago was to be the divine oracle on all matters relating to climate change, is now to be just one input into the government’s response, a draft version of which is scheduled for next week.

And you can bet that the opinion polls will be another input, and here the signs are already ominous. There is still a general feeling that something has to be done about climate change, but the level of support drops like a brick as soon as the idea of cost is raised.

Rudd in a worse position to introduce unpopular measures than any of his predecessors. When Bob Hawke and Paul Keating brought in the free market reforms of the 1980s a lot of their traditional supporters were against them but they did have the backing of the parliamentary opposition. When John Howard brought in the GST, Labor opposed it fiercely but Howard’s own side of politics was united behind it. Rudd will be copping it from both sides.

Those of us who take a longer view and worry about our children and grandchildren can only hope he holds his nerve and presses ahead, as the Europeans and Japanese are doing; if he follows the pusillanimous advice of Nelson and opts to wait for the rest of the world, we’ll never get anywhere. But it is a big ask.

It’s the moment for Rudd, the mild-mannered bureaucrat, to duck into a phone box and re-emerge as Kevin 07, superhero. Well, we can dream.