Readers are no doubt aware that the question of whether or not the unusually large number of tornadoes in the US at the moment can be (partly?) attributed to climate change is the subject of much discussion in the media and blog-o-sphere.
Of course, "lukewarmenists" are on one side of the fence, as demonstrated by
Judith Curry, who ends a post which notes two sides of the argument this way:
Cumulative catastrophic weather events are being used to support the case for global warming action. Sorry Bill and Joe, but we need to look at each type of extreme event, in different regional locations, and then interpret them in the context of the local historical records, and then cumulatively in context with the teleconnection weather regimes and multi-decadal oscillations. Once we’ve done that and then find an upward trend in frequency and/or intensity that cannot be explained by problems with the data record or natural climate variability or weather roulette, THEN lets talk about the potential impact of global warming.
Even for a scientist who loves to talk up uncertainty, I think this is being very disingenuous. She may as well say: we'll have to wait for another 30 or 40 years to see if tornado rate really is increasing, and can understand long term patterns in tornado rate, before we could call this one.
Both sides acknowledge the difficulty of assessing the long term tornado record, because of issues with reliability of reporting, population and housing changes which make simple "death rate" comparisons pretty meaningless, and technology issues to do with radar, etc.
My hunch is that there is quite a bit of record keeping uncertainty for other extreme events too. For example, after the recent Queensland floods, skeptics liked to point out that the 1893 Brisbane River flood was much higher (and there were a series of floods that year.) However, what struck many here about this year's floods was their vast and protracted extent - from Rockhampton in the North, many hundreds of kilometers inland, then right down to the coast. My guess is that a really detailed comparison of the extent of rainfall in the whole of south Queensland between 1893 and now might be a bit tricky, given what I presume would be much more widely spaced rainfall records in 1893 compared to what we have now. (That may not be a correct assumption, and I guess river heights may be a good way of comparing the two years as a proxy for the total rainfall and its extent; but on the other hand you have modern dams which complicate that comparison. I would like to know what meteorologists think about this.)
Of course, the other point to note about Australian weather records is that you have none at all going back more than a couple of hundred years. I would guess that you only have widespread, reliable records going back 150 years.
Apart from the record keeping issue, I am sure Judith Curry would argue that there is a lot of uncertainty with understanding multi-decadal oscillations, yet she wants them fully understood before we can even start looking at the AGW attribution question. Curry's approach is just another of her ways of suggesting no political action on climate is appropriate for the foreseeable future.
On the other hand, Michael Tobis has had a series of posts about the whole attribution question, and his take makes much more sense.
In his first post about this, he ended with:
I think that we are seeing another instance of excessive attention to "attribution" in a statistical sense. The climate is changing with increasing rapidity. Some of the changes will be anticipated, some not. We shouldn't presume that changes will be locally monotonic. They won't be. Under the circumstances, we'll get extraordinary runs of just-the-sort-of-awfulness-we-get-around-here in various places as the system wobbles about. I mean, what did you expect?
In
a follow up post, he addressed this more broadly, using an analogy I like:
Now, this sort of outbreak event is not entirely unprecedented either, though it seems to be emerging as the single most severe instance in the satellite era.
But it's a, forgive me, black swan of a sort. One thing about really really severe events is that you can't do statistics on them. They are too rare to form a large enough collection to draw conclusions.
But you may have a flock of shouldn't-be-black stuff. Black doves. Black, um, pelicans. Black seagulls. Black other stuff. I'm not much on this bird business, but the thing is, although you know these things exist, and you know they are too rare to extract a trend, you shouldn't be seeing any of them very much.
Hot summers in Moscow. Year after year of flooding on the Mississippi. Huge tornado outbreaks. At what point do we get to look at the collection of weird events and say something is going on?
Let me admit, first of all, that there are all sorts of statistical warning signs associated with this question. Selection bias, observer bias, post hoc definitions. Our intuitions may well be misleading us.
On the other hand, there is the question of rolling a thirteen. The more we disturb the climate, the more excursions it will make into unfamiliar territory. As we perturb the climate, as it wobbles around more and more, it will more and more often hit these weird peaks.
Perhaps local events like tornados will show no trend, but tornado outbreaks, when they happen, will be more severe. The ocean, after all, is further from equilibrated with the atmosphere and with space. Air masses will encounter each other in unfamiliar ways. Perhaps strange things will happen. Perhaps (and I am not being Eli-style coy here, perhaps not) they already are happening.
As I say, I find this intuitively pretty compelling, and very appropriate to keep in mind when you read something from some climate organisation (like NOAA, which has been doing a lot of this lately) that says "climates scientists say there is no attributing .......insert latest wild climate event....to global warming."
Everyone knows that precise attribution is complicated and difficult - there have only been a couple of papers (one about the English floods, and I forget the other) which did dare to claim attribution of a couple of extreme events to global warming.
But that doesn't mean that it's not right to suspect that there is something to do with climate change if a number of extreme weather events start piling on top of each other, as they have in 2010 and (seemingly) 2011.
I don't know who first used the analogy, but while the long term predictions of climate change may be right about a warmer atmosphere having less tornadoes rather than more, the climate moving from one state to another may well be like a spinning top that has been given a big kick and wobbles back and forth for quite a while before eventually settling down into a new period of long term stability.
(Michael Tobis refers to that idea in his post, although he also makes the claim that people think of AGW and climate change in the wrong order, but I do find he gets a little confusing on that point.)
Anyway, while I don't wish death and mayhem on anyone, as far as I am concerned, if outbreaks of unusual extreme weather events continue for the next year or two, I would be happy to see them start to convince the public (and politicians) of the need to address CO2 production seriously and with urgency.
Update: I have been thinking how to summarise their respective positions. Is this fair?:
Curry: there's so much uncertainty about this, it's wrong for anyone to be referring to it having anything to do with AGW or climate change at all.
Tobis: the uncertainty as to how exactly climate change will play out means that the rapid accumulation of extreme weather events in the shorter term, even if they were not predicted as likely outcomes of global warming in the longer term, is consistent with climate change, even if you can't individually attribute events to climate change.
Me: Curry and all lukewarmenists like to play up uncertainty and must know that this is used for political purposes. As John Nielsen-Gammon's recent post (which I referred to recently) suggests, uncertainty as to being able to work out everything about past and current weather and climate is no killer reason for disputing AGW, which is likely to have major effects.
