Climate change is one of those (many) phrases that every reader/listener interprets in their own way. James Annan has interpretted it in one way in a discussion which I’ll summarise as “the a priori[^1] position that climate change would be detrimental has no scientific/logical underpinning”. (Well, actually I think he’s really expressing the converse: “that no change is the best possible outcome, is not necessarily wrong”; but it amounts to the same thing.)

Put in yet another way: Given that it’s unlikely that some cosmic conspiracy has put us a maximum of some sort of climate-ecosystem-human-society efficiency, it’s hard to argue a priori that change would be a bad thing, as it might take us somewhere better. (The metric of exactly what is better is irrelevant to the argument, but I was disappointed that James’ arguments were all pretty western hemisphere-acious.)

However, I think there’s a fatal flaw in this argument. I think one can argue a priori that the speed of climate change could be detrimental, even if the place one ended up was some how “better” (always assuming we reached an equilibrium before economic/ecosystem meltdown). It seems quite clear that neither existing human societies, nor natural ecosystems (if such still exist) can respond to a rapidly changing environment without detrimental impact.

So, my point is that climate change is a problem both in terms of magnitude and rate of change. Some of us are as much worried about the speed of change as we are of the eventual magnitude. (James does allude to the issue of rapid climate change in passing, but I think misses it’s importance in discussing whether the status quo may or may not be better than the result of climate change).

Given that the speed of change is at least as important (if not more so at some point) than the magnitude of the change, then arguments about our ability to adapt being relevant need to be taken with a grain of salt. The first question should not be whether we (or our ecosystems) can adapt enough, but whether they can adapt as quickly as things are going to be changing.

I think we now know that the speed of change is going to be a problem, but I would argue that actually the most likely a priori position would have been to expect just that: Anthropogenic climate change is most likely to be detrimental - if only because of the speed! And unlike James, I do think this is a logical position! [^1]: Here my definition (and I think that of James) is that a priori means “before we do/did any calculations that actually show the expected climate change would be detrimental”

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Two degrees of Warming (from “Bryan’s Blog” on (on Friday 09 January, 2009))

William asked what ML thought would happen with two degrees. I suspect the reason he asked that is that most of us believe that two degrees is in the pipeline, and pretty much inescapable now …

comments (7)

James Annan (on Monday 13 November, 2006)

Well, I agree with you in theory, indeed I did specifically (twice) refer to the possibility that the speed of climate change could in principle be a problem. But is there actually any evidence that the recent rate of change (<0.2C/decade) has been (or will be in the near-term future) a real problem in itself?

My feeling is that the scales are currently tipped clearly towards the positive, predominantly due to improved northern hemisphere agriculture and fewer winter deaths. Would we really return to the harsh winters of the 1960s, given the hypothetical choice?

Bryan (on Monday 13 November, 2006)

I understand that there are significant ecosystem stress issues: problems like early spring bringing plants out to flower before the insects are ready, leading to collapse of both species … this is one of the reasons behind migration of species, but migration may not maintain existing range and diversity. Secondly: while 0.2C/decade sounds small, it would seem to be the fastest sustained global change on record, and there is no evidence that ecosystems can adapt easily to this (maybe this is the same point :-).

Your second paragraph is still western-hemsphere-acious. I think those who live in Africa might not care about our winters. In Africa most might argue that climate change is already detrimental - whether anthropogenic or not, the point is that change is a problem for undeveloped countries. (In any case, I don’t think the harsh winters of the 1960’s would any longer have the impact they did then in the west anyway - even without increasing direct heating, insulation in homes has improved incredibly).

Finally, yes you did allude to the speed issue, but I considered that it was pretty peripheral :-)

James Annan (on Wednesday 15 November, 2006)

Hey, I’m in the Eastern hemisphere :-)

Regarding Africa, it seems that the most exaggerated and pessimistic predictions amount to less than 0.5% pa reduction in potential yield (which will still remain far above the current actual yield even 100 years into the future) in the worst affected areas (other areas show roughly equivalent increases).

More details here:

I don’t doubt that many people in impoverished countries are poorly equipped to cope with their existing climate (including its natural variability). I would be very surprised and disappointed if this theoretical worst-case rate of <0.5% per year in potential yield reduction was at all significant compared to the rate of social and economic development which these people (presumably) aspire to. Any focus on AGW in this context seems completely misplaced.

Bryan (on Wednesday 15 November, 2006)

Hmmm. I knew I shouldn’t have taken you on … I don’t have enough time to refute your points in detail … but then I don’t feel I have to.

I’m simply suggesting, a priori, climate change speed may be a bigger problem than the magnitude (you concede this in your googlegroups discussion in the context of pesticides and antibiotics).

Given there is no possible upside to the speed issue (it’s either cope-able with, or it’s a problem), then a priori, one can argue that the probability is it will be detrimental:

(a0 +bnegative) = b*negative which is negative!

(And we should leave it there, because I suspect you could sink me with detail now I’ve mentioned the probability word :-)

Fair call on the hemisphere issue!!

James Annan (on Friday 17 November, 2006)

Well, I hope I’m not boring you to death but your argument seems to be that there is a nonzero probability of (the speed of) AGW being bad, which I would certainly not dispute. However, that’s some way removed from what I was trying to object to, which was the belief that the current climate was clearly optimal for us (and furthermore that this could be considered a fundamental truth, not the result of careful consideration).Bryan (on Friday 17 November, 2006) Not so much bored, as dealing with competing priorities :-)

I don’t dispute your last point, but my point is that whether or not it’s optimal is not the whole story, it may well be that we may not be able to afford (for social, political, ecological, or economical reasons, any of which may not yet be well quantified) to deal with climate change.

Bryan (on Friday 17 November, 2006)

I suspect we are now agreeing vociferously :-)