Friday, September 15, 2006

Climate: UK numbers and US rumours

The report from Kevin Anderson and colleagues at the Tyndall Centre outlining how the UK could "do its fair share" in keeping global atmospheric concentrations of greenhouse gases below 450ppm looks like a serious, professional bit of work (press release here, full report -- a 175 page pdf -- here, sensational Guardian coverage here). It charts a route to reducing UK emissions by 70% by 2030, with greater cuts beyond that.

Also interesting is a report in Platts that the Bush administration "may announce as early as next week a goal of stabilizing carbon dioxide levels in the global atmosphere at 450 parts per million by the year 2106".

This rumour, if proved true, looks like a canny bit of political triangulation: seize your opponents' issue and sound visionary while not actually committing to anything that requires real action or pain. 2106 is like 110 years from now, man. Dave Hamilton of the Sierra Club is reportedly of this view, saying that the stabilisation target should be reached much sooner, and by 2050 at the latest.

But Jon Gibbins argues it is not as simple as that: atmospheric concentrations will actually have to be lower than 450ppm in 2050 if (barring what he thinks are unlikely developments in capacity to draw down CO2 from the atmosphere at an accelerated rate) there is to be a chance of stabilising at that level by 2106. If correct, this would mean that if the Bush administration were serious about their target they would have to act even more urgently than even their harshest critics suggest -- a corollary that may have escaped them so far.

The reasoning here is simpler than I may have made it sound. An explanation from Jon is attached, with his kind permission.

1 comment:

Caspar Henderson said...

First statement by Jon Gibbins:

Leaving aside whether or not Bush is actually proposing anything, it is worth considering which is better:

a) Stabilising at 450 ppm by 2050

b) Stabilising at 450 ppm by 2100


(i) that we cannot remove CO2 from the atmosphere (if we can then the debate changes anyway);

(ii) bearing in mind that natural processes reduce CO2 concentrations relatively slowly even if we stop emissions altogether;

(iii) that CO2 emission rates will be falling from 2050 to 2100 in plan (b);

Then statement (b) implies that in 2050 atmospheric concentration will have to be lower than 450 ppm (and will then rise, fairly slowly, to 450 ppm over the second half of the century).

Thus at any time out to 2100 plan (b) will have lower atmospheric concentrations of CO2 than plan (a) and warming (and ocean acidification) effects will be lower.

Emission rates are higher before 2050 in plan (a) than plan (b) and lower after 2050 and total emissions would be almost identical. But the effect of having the emissions earlier in plan (a) is to increase the time over which they are in the atmosphere causing heating. Making the emissions earlier also precludes stabilising at an even lower level than 450 ppm when we realise how easy, and useful, that would be.

So on all considerations plan (b) appears better than plan (a) and should be encouraged in preference to it?

Question put to Jon Gibbins by anonymous:

Thanks, Jon. I’m pretty sure the environmental position here is to stay at 450 or below after 2050 through 2100 and beyond. Doesn’t that change your analysis considerably?

Reply from Jon Gibbins:

Stable atmospheric concentration at 450 ppm after 2050 is assumed.

But there is also an assumption that we cannot reasonably expect to be able to reduce atmospheric concentrations before 2100, but can only have them increase or stay level. In that case if they don't level off before 2100 then they must be rising, and if 450 ppm is the point at which they level off in 2100 they must be lower than 450 ppm before then (and rising towards it).

It might be assumed that atmospheric concentrations could go higher than 450 ppm and then go down again in a plan that assumes stabilisation at 450 ppm in 2100, but that seems very unlikely. This would require either:

(i) a method to remove large amounts of carbon dioxide from the atmosphere; or

(ii) emission rates to be significantly lower than the level for stabilisation at 450 ppm for an extended period before 2100 - but even for zero emissions the rate of fall in atmospheric concentration is pretty low (hard to say what the actual number would be by then, since the inevitable warming will probably tend to stop or reverse many of the natural sinks)

So any realistic (i.e. not relying on magic ways to remove CO2 from the atmosphere) path to stabilise at 450 ppm by 2100 implies more urgent action than for stabilisation at 450 ppm in 2050, to hit a target lower than 450 ppm in 2050, which then leaves the children and grandchildren with a more manageable target for the period 2050-2100, essentially just continuing what has been happening before as they push net emission rates down from some higher value in 2050 to the value for stabilisation at 450 ppm in 2100.