I find that I need to understand the “defining dangerous climate change stuff”. Up to now I’ve rather dismissed it as someone else’s problem but now I need to know more. This is not a very satisfactory post, in part because I ran out of time to finish it. Its more a request for feedback, possibly based on some of the below. Where do I find a good (but not too long) discussion of the (ecological, mostly) effects/risks of climate change, with a reasonable amount of quantification. Not just wurbling about polar bears, but something more concrete.
The EU ended up deciding on 2 oC but I don’t know if they even attempted to justify that. the German Advisory Council on Global Change (WBGU) also ends up with 2 oC. It says:
The key goal of the UNFCCC is to stabilize greenhouse gas concentrations at a level that would prevent dangerous anthropogenic interference with the climate system. Article 2 of the Convention defines this in specific terms: Ecosystems are to be able to adapt naturally to climate change, food production is not to be threatened and economic development is to be able to proceed in a sustainable manner. The Council has examined each of these three criteria with regard to the threshold from which climate impacts would no longer be tolerable. The present state of science does not yet make it possible to derive these ‘guard rails’ stringently and quantitatively from the climate impacts that must be prevented. The WBGU was thus limited to providing a qualitative assessment, based on its own expertise and on commissioned external reports and study of the literature. With regard to ecosystems, the effects of climate changes are already apparent today. The threshold from which damage to the global natural heritage is no longer acceptable cannot be determined precisely. However, the WBGU estimates it to be in the range of 2°C global warming relative to pre-industrial values. For worldwide food security, too, the threshold appears to be in this range, as above this global warming level worldwide climate-related losses in agricultural production must be expected, as well as a steep rise in the number of people threatened by water scarcity. Concerning health impacts, no tolerance threshold can currently be appraised due to poor data availability and a lack of mature methodologies. However, it can be assumed that for some regions the effects of climate change would already lead to intolerable impacts at 2°C mean global warming. Moreover, climate change has the potential to trigger singular, catastrophic changes…
But do we believe this? Take the health impacts… I don’t like hot summers myself, but thats because my environment is poorly adapted to them. My SW facing office windows have no external shading, nor does my house. Plenty of people already live in places far warmer, and appear to lead tolerable lives. I don’t think I really believe the human health bits, nor am I convinced by the agriculture stuff so far. The ecosystems seems more plausible. So do they justify their limits? Reading on:
The primary limit: Global mean temperature The upper limit of absolute global warming of 2°C relative to the pre-industrial temperature was based on the observed range in the recent Quaternary period (over the last several hundred thousand years), that has shaped today’s climate and the development of humankind. The highest observed global mean temperature in this period was 1.5°C above the pre-industrial global mean temperature.The Council added 0.5°C in its 1995 annual report to account for improved adaptive capacity… intolerable changes in the
composition and functioning of today’s ecosystems could not be ruled out if the global mean temperature rises by more than 2°C
So… if thats how they got their 2 oC, clearly it *isn’t* based on human health or agriculture: its far more based on a lets-not-exceed the past type approach (incidentally I think the knowledge of Quaternary temps isn’t really good enough to be saying this stuff anyway). Or is it just a co-incidence that the two approaches produce the same number? How useful is “could not be ruled out” as an assessment of probability? Could we rule out the risk of economic collapse if we restricted out CO2 emissions (this is, I think, from JA).
the Council had to rely on expert assessments based on reviews of the scientific literature (e.g. IPCC, 2001b; Hare, 2003)
IPCC 2001b is the TAR WG II; Hare is largely based on it (so it says; incidentally Hare is *Mr* Hare and while I wouldn’t pretend that all good science is done by people with doctorates most is; and Mr generally implies a lowly rank; but I know nothing else about Hare so may be maligning him). Then I get to his fig 1 (p12) showing the proportion of species at risk of extinction… which is all very well but surely this is non-climate-related pressures, just general human encroachment (OK, so it doesn’t make them any safer but it doesn’t justify climate-related action).
And then I ran out of patience… there is far too much there to read. I get the impression of lots of uncertainty. I’m happy with the argument “lets not do climate change because the risk of ecosystem impact is high/medium/unquanitifiable” but I’m not sure how well it plays in general.
In an effort to find some numbers, I looked at the Stern review again. They have some post-publicaiton ruminations, I read http://www.hm-treasury.gov.uk/media/B6F/58/paper_a.pdf. The first thing that caught my eye was:
But even at low levels of warming, there are already significant impacts on vulnerable communities. Rapid warming is causing serious challenges for indigenous communities in the Arctic Circle, and some low-lying tropical islands have already been evacuated.
This *isn’t true*. Nowhere has been evacuated due to sea level rise (or increases in hurricanes). And (as ever) the major impact on Arctic communities is collision with The West (to their betterment, if you believe Ms Smillas feeling for Snow, which I’ve just finished, on the grounds that nowadays its very rare for Inuit to die of starvation. But that is only a novel so please don’t take that too seriously). But the interesting point is that Stern (like the other reports, though I didn’t quote those bits) wants to say that we are *already* suffering damage due to climate change. If he has good evidence of this, why is he putting forward nonsense? Stern continues that “Climate change is all about risk and uncertainty” and indeed this seems to be his current “Frame”.
[Update: several people referred me to WGII, though in a "here is a pile of stuff I haven't read" sort of way; elsewhere mt said "the WG II process produced a useless mess"!
NS provides a link to the Exeter report and a editorial essay by Hansen, though that is mostly the usual stuff about how everyone else is wrong and massive sea level rise from ice sheets is likely soon.