John Nielsen-Gammon, our Texas State climatologist came up with this scary image that most of you have seen, and that everyone in Texas ought to take a good long look at. I was one of the first to reproduce it, but I’ve seen in lots of places since, and with good reason.
Unfortunately, John has followed up on this contribution with what I consider a mistaken article, wherein he claims that
“Texas would probably have broken the all-time record for summer temperatures this year even without global warming.”
Before we get into his argument and its drawbacks, let’s note the obvious. We see that this years drought/heatwave is far outside the observed pattern distribution of events.
It’s hard not to take note of the tremendous similarity of the situation here to Australia’s a couple of years back
, though Australia’s droughts are on the other end of the El Nino seesaw. (Australia has, in fact, been extraordinarily wet of late.)
So is it a “New Normal”? Is Texas in perpetual drought now? Will we swing back and forth out of unheard-of droughts and unheard-of floods? Will Australia do the same, along with other parts of the formerly semi-arid subtropics? Certainly this is the intuitive impression that many of us come away with. Barry Brooks is no amateur, and he was at least willing to quote a colleague saying
“Given that this was the hottest day on record on top of the driest start to a year on record on top of the longest driest drought on record on top of the hottest drought on record the implications are clear…
It is clear to me that climate change is now becoming such a strong contributor to these hitherto unimaginable events that the language starts to change from one of “climate change increased the chances of an event” to “without climate change this event could not have occured”.
Clearly, we can say similar things in Texas this year. But should we? Nielsen-Gammon says we shouldn’t.
Let me summarize his argument:
- The temperature anomaly this summer is about 5.4 F
- Global warming to date has led to a local warming of Texas summertime temperatures of 0.5 F, so the temperature anomaly can be divided into 0.5 F background warming + 4.9 F other warming.
- There is a strong correlation between annual rainfall variation and annual temperature in the graph. N-G finds a second order curve that fits the data [
about as well as the linear fit] (see comments), and figures that the low rainfall could account for most of the remaining 4.9 F
- He sinks into the tea-leaf territory of the “AMO” and claims to pick up the balance
- Leaving aside the odd idea of superposition of temperature anomalies and the very weak evidence for the AMO, clearly there is a plausible claim that the huge temperature anomaly is “mostly” “because of” the drought
- There is no obvious trend in Texas toward drought, so climate change does not cause unheard-of droughts
- Therefore this is a fluke and has nothing to do with climate, or that other fluke in Australia in ’09, or all the other flukes we have been seeing lately
I don’t buy this for a minute. I am, in fact, shocked by the seriousness with which this argument is being taken.
It is interesting that when I have run this by non-experts, they all think it is crazy. Are they right?
I’ve been struggling for an analogy, and have come up with nothing resembling a realistic real-world example that allows this fallacy, so allow me a parable instead.
There is a small, isolated urban country where the wild fauna have been eliminated, and the public is only familiar with pets: dogs, cats, hamsters, and a few horses used in ceremonial events. The entire population knows very little about other animals, and even the experts have acrimonious debates based on fossil records and old paintings, just as we are familiar with contemporary climate but have to extrapolate to ancient or future climates.
One day, there is an earthquake. Not only does a border fence fail, but that fence abuts on the neighboring country’s great zoo. Many animals escape into our urban country, and it happens that one of them is an elephant, which they will perceive only as a large, bizarre animal.
However, our experts have been observing the zoo from a distance. They believe they have a good idea of the number of animals at the zoo from the number of feeding stations (visible from an observation tower), and a good idea of the total mass of the animals (calculated from the size of the food deliveries). They conclude that the average zoo animal is the size of a large dog. Therefore, the elephant is not an escapee from the zoo! It must be an extremely unusual dog or cat.
That’s the best I can do. It makes no sense, does it? We have an invasion of phenomena which we have only weak characterization for. We have some idea of averages and trends because of physical constraints, but we know very little of the nature of outliers in the changing climate.
(This is to say nothing of anomalies due to transient climates for the present.)
Here is the thing. We are increasingly disturbing the climate. A truly bizarre season occurs in a particular place. Either these extraordinary events are connected, which is perhaps unlikely, or they are unconnected, which is extremely unlikely. That is, you are asking for a bizarre coincidence.
But now we add up the number of bizarre coincidences, for each of which John can make comparable arguments. The tornado outbreak this spring. The huge blocking event in Asia last summer which did so much damage in central Russia, Pakistan, and parts of China. The fires in Australia in 2009 and the floods this year. The floods in the midwest. Heat waves in Europe.
None of these are clearly part of local trends. None of these are particularly predicted in the literature, and as far as I know the GCMs don’t indicate these things happening.
But, here’s the thing. They are happening.
So when I look at John’s plot, I see that there are only two possibilities. First, a bizarre coincidence as John suggests: a gigantic grey housecat with big teeth, floppy ears, enormous legs, and a strange nose. Second, an unexpected consequence of climate forcing. An elephant.
That is, what we have is not because of a change in the mean but because of a spreading, an expansion of the cloud of possibilities. From a dynamics perspective, that’s not surprising in the least. We’re passing, year by year, from one climate configuration to another at a very rapid pace, and we are used to thousands of years of unusual stability.
Does anyone actually expect “global weirding”? Well, I am not sure how we should specify an a priori metric for it, and without one we can’t really formally detect it. And the models, well, we already know that the non-assimilating GCMs are very stingy with extreme events. Why? My theories on that are too vague for publication, but it’s widely known to be true.
But when I see a graph like that one, I don’t find myself saying, hmm, obviously not part of the trend, therefore natural.
Now my other analogy is emotionally fraught, and let me apologize if it offends anyone, but I have to say it. When I saw a couple of 100 story buildings falling down, I didn’t say, there’s no anthropogenic trend to date for buildings to fall down so they must have fallen down naturally.
I’m sorry, but I find that argument, ahem, less than compelling.
Let me offer a couple of simple propositions instead.
- There’s a first time for everything.
- If you push something hard enough it will fall over.
I for one think the fan is no longer pristine.
I think it’s time to take this bull by the horns. You can’t apply small-signal arguments to large signals in nonlinear systems. So please stop it.
Update: Via Google Plus, Jonathan Abbey summarizes my argument nicely:
Climate characterizes the statistics of weather and the statistical bounds of weather. If we start seeing weather patterns change, that can indicate a change in climate.
The question is all about how likely it is that this weather would occur if the statistical parameters of the climate were held fixed as it has been since instrumental records began, say.
If weather like this is sufficiently unlikely under our previous understanding of regional climate, it may be (a piece of) evidence that the climate is itself experiencing a dislocation.
Which is sort of interesting.