As tempting as it is to tell Judith Curry to “Do the math!” — I don’t think she can handle it.
A recent post at WUWT quotes her saying this little gem:
It is possible that a shift to the cold phase of the AMO is underway, which would extend the warming hiatus for ~2 decades.
That made me wonder, what does she think a “hiatus” is? What’s her evidence for it?
I managed to find a post on her blog where she tells us. A hiatus, according to Judith Curry, is when
1) the rate of warming over a particular period of at least 10 years is not statistically significant from zero (with the context of a nominal 0.1C uncertainty)…
It’s almost impossible to believe that anyone who seriously claims to be a scientist would accept (let alone propose) such a ridiculous definition. Yes, she really means that any 10-year or longer trend estimate below 0.1 °C/decade is a “hiatus.”
If you’re wondering what “nominal 0.1C uncertainty” means, it should mean that the standard error (the likely difference between estimated and true trend rates) would be about 0.1 °C/decade. It turns out that for 10-year time spans, that’s quite close. It’s about the only thing she gets right.
Since Judith Curry’s post includes “show me the data” in its title, let’s look at some data. She shows graphs of data from NASA, from HadCRU, from NOAA, from the Berkeley Earth Surface Temperature project, from reanalysis (both ERA-interim and CFS), and — of course — troposphere temperature from UAH (but not from RSS). All we’ll need is one of them, so I’ll use the data from NASA. I’ll use yearly averages rather than monthly data, because the autocorrelation in monthly data is so strong you can’t afford to ignore it, and I don’t think Judith Curry can handle that. Here it is since 1975, with the estimated trend using least squares regression:
The estimated warming rate is 0.18 +/- 0.03 °C/decade, and that’s a 2-sigma error range for roughly 95% confidence. We conclude that the increase from 1975 to the present (the final figure for 2018 is year-to-date) is statistically significantly different from zero.
Now let’s use Judith Curry’s definition to look for a “hiatus.” I’ll test every 10-year time span to see whether or not the estimated rate is below her 0.1 °C/decade limit. Here are the results, in graphical form:
Every place one of the circles (the estimated trend rate) dips below the blue dashed line (the 0.1 °C/decade limit) meets Judith Curry’s definition of a “hiatus.” By her standard, there are 10-year “hiatuses” centered on 1982, 1983, 1985, 1991, 1992, 1993, 2006, 2007, 2008, 2009, and 2010. That’s a lot of hiatuses.
But wait — maybe she would insist that they’re not all separate “hiatuses,” they should be combined into longer “hiatuses.” After all, she did say “at least” 10 years. We can do that. Let’s look for even longer time spans with an estimated trend rate below 0.1 °C/decade. We can combine all those “hiatuses” into just two of them: an 18-year span from 1979 through 1997, and a 16-year time span from 1998 through 2013. If we plot those two “hiatus” trends we get this:
There’s a sizeable “jump” from the one to the other. I wonder whether Judith Curry actually believes this is a realistic portrayal of the temperature trend since 1975. If so, it might remind you of something.
There’s also the fact that longer time spans result in smaller standard errors of regression analysis (smaller “nominal uncertainty”). For the 18-year time span the standard error is less than half her 0.1 °C/decade “nominal uncertainty” so the trend actually is “statistically significant from zero” (she really means statistically significantly different from zero). The same is true for the 16-year time span. But by Judith Curry’s standard they’re not. Her standard doesn’t seem to involve actual statistics — at least, not done right.
If Judith Curry can declare a “hiatus” for any 10-year time span with an estimated trend rate just 0.083 °C/decade less than the overall 1975-present rate, then using the same “logic” why can’t I declare an acceleration for any estimated 10-year trend rate more than 0.083 °C/decade more than the overall 1975-present rate? Doing so would allow declaring acceleration centered on 1980, 1987, 1997, 1998, 1999, 2012, and 2013. That’s a lot of accelerations.
But of course I should combine some of them into longer accelerations. That leaves three: a 10-year span from 1975 through 1984, a 16-year span from 1992 through 2007, and a 13-year span from 2006 through 2018. Those trends look like this:
Seriously — if I went about declaring regular episodes of acceleration in global warming based on that (which is Judith Curry’s logic), how would Judith Curry respond?
And then there’s the fact that using Judith Curry’s logic, some of the “acceleration” episodes overlap with some of the “hiatus” episodes. In fact two of the “acceleration” episodes overlap with each other. How is it that by Judith Curry’s statistical standard, a given point in time can be in both an “acceleration” and a “hiatus”? How can the years 2006 and 2007 be part of two different “accelerations” and a “hiatus”?
Of course it’s all nonsense. There is no evidence of either “acceleration” or “hiatus” that stands up to scrutiny, when you do the statistics right. Judith Curry didn’t. My opinion: she can’t.
What she did is pick a ridiculously short time span to allow herself to declare a “hiatus” because the uncertainty in such short periods is so large. As for even doing basic statistics right — let alone any of the more sophisticated stuff that really is needed to get it right — I don’t think she can handle it.
She also gives an alternate definition of what makes a “hiatus,” a “2)” which has to do with model output. That’s just ignorant; there was or there wasn’t a “hiatus,” regardless what model results say. She further adds a “3)” about how anything exceeding 17 years is really truly definitely a “hiatus” — but she doesn’t require that, 10 years is long enough, and any trend estimate less that 0.1 °C/decade is low enough, for her to declare “haitus.” The “model output” thing is irrelevant. The “17-year” thing is based on faulty analysis by others, which ignores the multiple testing problem. But I don’t expect Judith Curry to get that either.
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Open Mind 
A.k.a. the logic of the boiled frog.
There is a good reason why null hypothesis statistical tests (NHSTs) are set up so that you argue AGAINST the null hypothesis (i.e. the null hypothesis is the thing you want to reject in order to continue with your research hypothesis), which is that otherwise you really need to consider the statistical power of the test. I am not unduly surprised that the general public doesn’t understand this, but eminent professors of subjects where NHSTs are used really should know this. NHSTs are not symmetric, it matters what you choose for your null hypothesis, as the test assumes H0 from the outset. If you want to claim there is a pause in warming, then you need to produce statistically significant evidence for a change in the rate of warming, i.e. reject the null hypothesis of no change in the rate of warming. Here is my attempt at explaining it.
If only someone had pointed that out at the time on Prof. Curry’s blog. ;o)
It is truly astounding how many apparently well-educated and intelligent people think that failing to reject the null hypothesis proves the null hypothesis. Not well-educated in that subject I guess.
Tamino, the comment I made on Twitter was a summary of my thoughts on “the hiatus” and “the AMO” as closely as I can remember them, sort of a review. I did not particularly bring in my personal opinions into this, other than the framing of my points. So asking me to retract a point made in a tweet in a review of my thoughts is, well, pointless. your attempt to rebut my points are full of logical fallacies and arguing at points i didn’t make. As a result, my theses look even more convincing. Once you’e in a hole, you can try to climb out or keep digging. Well keep digging, Tamino. My final words: read my blog.
Almost too subtle… if you don’t click the link.
I didn’t click the link, and originally thought “where the heck did this come from?”
Now that I’ve followed the link, I’m thinking “what a travesty of a brain those comments from JC are”. A fascinating thread. The “oh, Gavin, you’re so mean” comments are almost unbelievable – that people could think JC’s comments are a shining light only confirms in my mind how dark and deep the hole is that some minds inhabit.
Whenever I read Dr. Curry’s blog I’m always struck by how amateurish she sounds. I’m not an expert on climate change or statistics, but I am a scientist and the stuff she puts up for the public is almost always hand-waving and bad arguments, along with a dash of conspiracy theory. When I read mainstream climate scientists I can tell I’m looking at an expert because they brings in details and numbers, with appropriate caveats, that show the extensive work in the field. In principle they could be wrong, but they at least look and sound professional. When I read Curry I can’t distinguish her from any number of random hacks on the internet.
Josh (and Thomas Peterson below), Judith Curry’s publication history is an interesting one, and if you look carefully at authorship and publication years is seems (at least, to me) that for most of her career she largely rode on the coat-tails of her coauthors.
From my own experience with publication and author contributions I am left with the impression that Curry’s skill wasn’t so much in producing good science, or in cultivating a comprehensive understanding of the science, but in networking with colleagues who had these abilities. Around 2006 she appears to have lost – or at least had diminished – her capacity to ride the train, and that is when she looks to have climbed onto the denialati’s bandwagon in order to keep a profile and some degree of attention. I don’t know if there’s any sort of cause/effect relationship, but it’s consistent with the overall apparent narrative.
A few years ago I posted on HotWhopper a cursory breakdown of Curry’s publication history. It follows her piggy-backing and her decent to irrelevance, and ended at a time where she was effectively only garnering publications on the basis of obfuscation of the science of others. I was going to update it a couple of years ago but she finally blinked out from research altogether and (unsurpisingly) retired, so the previous trawl is pretty much reflective of the final result.
As far as I can see, what Curry does now is not science, it’s an avenue for ongoing attention and profit. Expressed mathematically:
{Science} ∩ {Curry} = Ø
Your opinion is that “she can’t” do statistics right. Is that because you think she doesn’t understand statistics well enough or because you think she can’t get the results she wants if she does the statistics right? I’ve always viewed the mere use of the word “hiatus” as an indication that the speaker knew global warming was real and knew that the observed warming would resume shortly. I’m still perplexed as how we can have so many record warm years recently and still see someone in 2018 say “extend the warming hiatus” as if we are still in one no matter what definition one might care to use.
Since Dr. Curry is choosing to focus on 10-year trends, it’s rather odd that the last 10 years show what is probably the highest warming trend* in the record (and definitely during the modern warming era)–yet still, somehow, in her mind the ‘hiatus’ apparently continues.
*0.33 C/decade for HADCRUT4, and by eyeballing Tamino’s graph #2 above, something like 0.38 for GISTEMP.
Willful ignorance.
https://rationalwiki.org/wiki/Willful_ignorance
I find it sad that a woman of her stature has thrown away her academic standing with such nonsense.
Having the chattering idiots in the denial echochambers lookup to you would be a poor substitute for the respect of your peers.
Ok, let’s say she’s right, we are all noobs in statistics and she has proven that there is/will be a hiatus due to a “cold phase of the AMO”. From a physical, rather than mathematical point of view, what she is basically saying is that “wow, look, no surface warming, it’s all going into the sea”. Now tell me how would this disprove the thesis that the Earth as a planet is warming up? It’s a well known fact that most of the radiative forcing is going into sea warming rather than air, so there wouldn’t be anything to celebrate anyway.
One can look at this from the opposite direction: power. That is, for a given series of length n years randomly selected using the parameters from the regression of GISS from 1975-2018 (2018 ytd) of trend = 0.018325 and residual error = 0.09645 how many times will the trend estimate be be below .01. If my quickie R code is correct, sampling series lengths from 10 to 20 years (by 2s) leads to the following percents of trend estimates below .01:
10 years: 22%
12 years: 15%
14 years: 10%
16 years: 6%
18 years: 3%
20 years: 1%
That is, finding series trend estimates below ,01 is quite common simply by chance. These numbers for 10 years differ from tamino’s percents because these are generated from independent samples not a sliding window.
Note that the commonly held maxim of needing 17 years to establish a trend using climate data fits right in with this analysis.
I suspect Aunt Judy is just fine with there being inexplicable surges and slow-downs, as it supports her contention that that the climate is beyond all human understanding and that after contemplating it, the only appropriate response is to retire to the fainting couch to clutch one’s pearls and nurse a mint julep.
Actually, I’ll have to remember the julep for my next forced excursion into denialati territory. (But I draw the line at pearls.)