By taking a position against a unilateral national emissions trading scheme in today’s Liberal leadership ballot, Brendan Nelson took a punt that most Australian voters are unlike my friend Wayne.

Wayne arrived in Canberra late on Friday night after spending more than five hours on a bus which got caught in Sydney traffic. He’s not rich but he can at least afford a Virgin ticket, so I asked why he chose not to fly.

“Save carbon,” he said.

Think global, act local. Noble stuff. But it’s a shame his altruistic self-sacrifice didn’t actually reduce CO2 emissions by causing the cancellation of any flights between Sydney and Canberra.

In the long run he hopes thousands of such small decisions could cause a cut in scheduled plane flights. It’s a long shot — the trend is very much in the opposite direction. According to a forecast released in June by Infrastructure Minister Anthony Albanese, the number of passengers carried by Australian domestic airlines is increasing 4% annually and on-track to double over 20 years to more than 200 million a year.

There’s still a place for altruism and self-sacrifice. At the bottom-line it makes you feel good to be part of a solution rather than a problem. That is probably the judgment a majority of Australians have been making recently when they’ve told opinion pollsters they support an emissions trading scheme which will raise the cost of the fossil-fuelled energy they use.

When the Garnaut Review delivers its final plan for an ETS at the end of this month it is likely to stick to its current recommendation to start with a carbon price of $20/tonne in 2010 and push it up over the ensuing decade to achieve the goal of reducing Australia’s 2020 emissions by 10% compared to 2000 when we emitted 550 million tonnes.

This has earned Professor Garnaut brickbats from industry (too hard) and environmentalists (not hard enough). So it goes. But a 55Mt reduction sounds impressive enough for Australians to think that would be a significant part of a solution to the global warming problem. It’s a shame, though, that this altruistic self-sacrifice will have as much effect as Wayne did by catching a bus rather than flying.

Last week I outlined the kind of contribution to global emission reductions that Garnaut reckons China might cop when the post-Kyoto negotiations reconvene in Copnhagen in November 2009. He said it would be “achieveable but difficult” to convince China to agree to limit its rate of emissions growth to half of its economic growth rate.

What would China’s emissions add up to if it accepted and adhered to such a regime?

Assuming its economy grows at 5%-10% a year, and coming off a base of 6.2 billion tonnes of CO2 emissions in 2006, that would allow it to increase its emissions by 150-310Mt a year. Pick a figure somewhere in between, say 250Mt. That would see China’s emissions grow by 1Bt every four years. Pick a more conservative, hopeful figure, say 200Mt. That would see China’s emissions grow by 1Bt every five years.

Come 2020, China’s total emissions would be topping 10Bt under the first scenario and 9Bt under the second. At the same time, assuming Australia has implemented an ETS according to Garnaut — and assuming it actually achieves the estimated 10% reduction in emissions — Australia will have reduced its emissions by 55Mt.

What would the payoff be for Australia’s altruism? The maths is pretty simple: subtract 55 from 3000 or 4000. Either way, it’s a big number. That’s a lot of extra CO2 in the atmosphere to hang around for many decades warming the planet, buggering up Australia’s farmers, cooking our Great Barrier Reef, and swamping our coastal retreats.

Add all the other countries whose emissions will continue to increase over coming decades and global emissions will be so humongous by 2020 that a 55Mt reduction by Australia will be seen to have been pointless.

This realisation will come sooner, most probably after the Copenhagen meeting which is unlikely to achieve any meaningful agreement. Global emissions continued to increase after the Kyoto Protocol was agreed, just as they will after a Copenhagen Protocol.

Australians will be expecting to begin paying extra for their carbon in 2010 so they will become more interested in doing the emissions maths to assess the value of their proposed contribution. The answers will probably erode their current commitment to a unilateral ETS, making it all the more challenging for the Government to introduce it in an election year.

Public attitudes in related policy areas can also be expected to shift. Getting approval for new coal mines and power stations will be harder, winning support for nuclear power will be easier, and the already exaggerated hope that renewable energy can replace existing baseload sources will be even more earnestly exaggerated.

Current alignments of industry, unions, environmentalists and other groups will become fluid. Isolationist notions could arise in the form of stronger calls to limit immigration and stop exports of coal, iron ore, alumina and other CO2 nasties. And climate change skepticism will become more attractive as the growing realisation that Australia is a climate-taker rather than climate-maker raises feelings of anxiety and powerlessness in the hearts and minds of voters.

Meanwhile, tragically good global citizens like Wayne will probably decide to cycle rather than even catch a bus, or just stay at home.

Brendan was after the majority of Australians who want to drive and fly until the hell and high water comes. In his first comments after replacing him as leader, Malcolm Turnbull began courting them too, criticising the Government for moving towards emissions trading before the Copenhagen outcome is known and saying that Coalition policy “will be informed by international developments”.

For the first time in Liberal Party history, it looks set to take a policy cue from what a Chinese Minister says in Denmark.