The most disturbing aspect of the Treasury ETS modelling — assuming you can handle the threat of a $5-7 a week rise in your energy costs — is the “reference scenario”, the ” business as usual” case of what happens if we do nothing about climate change.

It’s not, as Treasury points out, a prediction of what the world will be like in 2050 and 2100, but a projection, one which doesn’t take into account any efforts to address climate change.

It does, however, raise some troubling issues if as a planet we can’t get our act together sufficiently to reduce carbon emissions. Troubling, in particular, for Australia.

The Treasury modelling and the Garnaut Review’s no-mitigation scenario suggested the atmosphere would reach 750ppm of greenhouse gases in 2050 and 1600ppm by 2100. This would lead to a temperature rise above 1990 levels by 2100 of 5.1 degrees, or a worst-case scenario of 6.6 degrees.

This complements recent work by two Stockholm University economists who used a different model and a probability distribution to estimate a “business as usual” scenario for climate change and anticipated a median temperature rise (on 1900, not 1990, levels) of 4.5 degrees, with a worst-case scenario of 6.9 degrees, based on a median level of around 1200 ppm.

Greenhouse gas levels don’t naturally level off, by the way — they go on building, as does the temperature, after a lag of some years. That’s the elegant thing about climate change — even if we reduced our carbon emissions right now, we’d still have quite a few years of climate change impacts to deal with.

Garnaut discusses the likely impacts and costs of a “no-mitigation” scenario extensively. They are not confined to minor things like losing the Great Barrier Reef or Kakadu. They involve massive temperature-related deaths, coastal inundation, the destruction of much of the country’s agriculture, plus little problems like our major cities experiencing extreme threats to their water supply.

The impact of a temperature rise of 7 degrees is probably getting into apocalyptic territory. You’d figure Australia, along with much of the world, wouldn’t be amenable to human life much above subsistence level, if that. At least people then wouldn’t be worried about where to put their investments.

The point of this is not to indulge in disaster-movie speculation. Well, not entirely. The other significant point that Garnaut made about our situation is that Australia is the single most exposed country when it comes to climate change. We’re environmentally, economically and geographically right on the bleeding edge, and we’re only a small nation. In short, we’ll suffer more damage more quickly than everyone else, and we have less capacity to cope.

Unfortunately, as conservatives like to point out when advocating doing nothing, we’re at best 2% of the world’s emissions.

Think about that for a moment. Australia faces perhaps total disaster in the next 100 years, but we have no control over it. The rest of the world does. Americans. Europeans. Chinese. Indians. Russians. Our fate is in their hands.

The issue is not whether we should be leading the world or whether we’re moving too fast. The issue is whether the rest of the world — including countries like Russia that might be altogether more relaxed about global warming and its consequences for countries bordering the Arctic — will do what is necessary to prevent massive damage to this country.

Leading the world? You wish.

We’re climate change mendicants. Our fate is in the hands of foreign governments. We can only beg them to consider their own future when they’re making up their minds about whether they want to take action quickly. Some of them, having watched Australia make a mozza from flogging its mineral wealth in recent years, might see the funny side of Australians suddenly deeply worried about climate change, and suggest we reduce our own per capita emissions significantly first before coming to them for help. Others might not see what the rush is, given the relative impact in their own countries is much less than in Australia.

And they’re unlikely to be too fussed about losing the Great Barrier Reef or Kakadu, although our pleas might remind them they should pop down and check them out before they go.

As with many other debates, there’s an irrational element of nationalism in our approach to handling climate change. It’s the fault of all them foreigners, seems to be the view — we’re only 2%. Why should we do anything? Why not the Chinese? But we’ve forgotten the corollary of that — if it’s someone else’s fault, we can only politely ask them to stop doing it and hope they see that it is in their own interests to take action as well.