As I mentioned a little while back, I’m going to refrain (or at least try to refrain) from polemics on the subject of climate change in the future. As a first step, I’m happy to say that I’ve found a post by Andrew Bolt which I can recommend. Bolt links to this estimate by Damon Matthews that each tonne of CO2 emitted into the atmosphere changes the equilibrium temperature by 0.000 000 000 0015 degrees, that is 1.5*10^-12 in scientific notation. Noting that the carbon price is expected to reduce emissions by 160 million tonnes per year by 2020, Bolt makes the straightforward calculation that the emissions avoided in the year 2020 will reduce equilibrium temperature by 2.4*10^-4 or 0.00024 degrees.
Bolt stops there, perhaps having run out of time, so I’ll complete the calculation for him. Obviously to compute the impact of the carbon price we need to estimate the effect, not just for the year 2020 but for the entire period the policy is in place. That’s a complicated task, but let’s simplify by supposing that the policy stays in place until 2100 and that the 2020 reduction in emissions is maintained over this period. That gives a reduction in equilibrium temperatures of about 0.02 degrees, which coincidentally or not, is exactly what I estimated using a different method in a recent comments thread.
Of course, as we all know, this is a collective action problem – any one jurisdiction acting alone is not going to achieve much. Fortunately, most countries are doing something, even if they have adopted inefficient approaches like direct regulation in the US. So, let’s calculate what would happen if everyone adopted measures with effects comparable to those of the carbon price.
Australia accounts for about 2 per cent of the global economy, and about 2 per cent of total emissions (the latter depends a lot on which emissions are imputed where, but these estimates are imprecise anyway). So, if Australia’s effort with the carbon price is about average for the world as a whole, and these policies are sustained without change, Bolt’s calculation implies that the reduction in equilibrium temperature would be about 1 degree.
Bolt invites comments on whether such a reduction is worthwhile. Anyone who has looked at the impact of 1 degree of additional warming ought to agree that reducing warming by 1 degree yields a benefit far more than is needed to justify global adoption of policies like the current carbon price policy.
What this calculation shows is that we need to do more. Depending on your projections we need to reduce equilibrium temperatures by 2-4 degrees relative to Business as Usual. That will imply a carbon price at least twice as high as that implemented on Sunday. Comparing this week to last, I think we can probably bear the associated pain.
Bolt also links to this article by Michael Bachelard which states that the carbon price would reduce emissions by 5 per cent, relative to 2000, and gives an estimate by Roger Jones that this would reduce equilibrium temperature by around 0.004 degrees. As I’ve pointed out quite a few times now, the relevant comparison, and the one I’ve used in my calculations is between the carbon price and business as usual. That comparison yields a reduction of 25 per cent, and an impact of 0.02 degrees using Roger’s sensitivity assumptions. So, it looks like agreement all round.
(H/T John Humphreys)