Guest Post by Jeff Id:
“Tamino” has made a couple of posts on how the last 10 year drop in temperature is not statistically significant, so it isn’t real. He went too far in his last one and began claiming it was a tactic of some kind of creature called a denialist to confuse and confound the public.
Let’s see what Tamino has been saying on his blog link HERE.
Some of you might wonder why I make so many posts about the impact of noise on trend analysis, and how it can not only lead to mistaken conclusions about temperature trends, it can be abused by those who wish deliberately to mislead readers. The reason is that this is still a common tactic by denialists to confuse and confound the public.
I just hate bad science. First he points out how Bjorn Lomborg made some comments about temperature decreasing, after placing the ever more popular label of denialist on him implying Lomborg’s statements were intended to confound and confuse the public. Heres the main point of what Bjorn Lomborg said.
They (temperatures) have actually decreased by between 0.01 and 0.1C per decade.
Ok, so graphs like the one below are the reason Bjorn Lomborg is a denialist.
I copied this graph from Digital Diatribes of a Random Idiot – A great unbiased site for trends (link on the right). Note the slope of -.0082 (.01C/month units or .00098 degC/year – Thanks to digitial diatribes comment below) in the equation on the graph. Most of us know this is actual data and is correct, in fact every measure is showing similar results. The earth stopped warming- a very inconvenient truth. So Tamino what’s the argument, why are the evil and uncooperative denialists wrong?
Statistics of course.
Here comes the numbers from Tamino.
The most natural meaning of “this decade” is — well, this decade, i.e., the 2000’s. So I computed the trend and its uncertainty (in deg.C/decade) for three data sets: NASA GISS, RSS TLT, and UAH TLT, using data from 2000 to the present. To estimate the uncertainties, I modelled the noise as an ARMA(1,1) process. Here are the results:
Data Rate (deg.C/decade)
Uncertainty (2-sigma)
GISS +0.11 0.28 RSS +0.03 0.40 UAH +0.05 0.42 All three of these show warming during “this decade,” although for none of them is the result statistically significant.
Ok Tamino has calculated GISS, RSS and UAH. One ground measurement and two satellite. For those of you who don’t spend their afternoons and weekends digging into this. ARMA is a fancy sounding method for what ends up being a simple process Tamino has used to estimate the standard deviation of the temperature. Sometimes it seems the global warming guys believe the more complicated the better, but no matter. He has a 2 sigma column which represents about 95%. He then goes on to say that because of the sigma 0.28 or 0.40 is bigger than the trend, the trend is not statistically significant. He repeats the comment below.
Let’s make the same calculation using data from January 1998 to the present:
Data Rate (deg.C/decade)
Uncertainty (2-sigma)
GISS +0.10 0.22 RSS -0.07 0.38 UAH -0.05 0.38
Finally one can obtain negative trend rates, but only for 2 of the 3 data sets. But again, none of the results is statistically significant. Even allowing this dreadfully dishonest cherry-picked start date, the most favorable
Now Tamino claims to be a statistician so I can’t see how he made such a simple boneheaded error but if he wants to pitch softballs, I’ll hit em. Just to make sure he’s in good and deep here’s one more quote.
I’ve previously said “Those who point to 10-year “trends,” or 7-year “trends,” to claim that global warming has come to a halt, or even slowed, are fooling themselves.” I may have been mistaken; is Lomborg fooling himself, or does he know exactly what he’s doing?
So, Mr. Lomborg, we’re all very curious: how did you get those numbers?
Wrong turns everywhere
The first and really obvious error Tamino makes is referring to the short term variation in temperature as noise. Noise in the context of sigma is related to measurement error. How can we determine the measurement error of the three methods GISS, RSS and UAH. Well the graph of the three is below.
The first thing you notice from this graph is that the 3 measurements track each other pretty well. The signal is therefore not completely noise. Well what is the level of noise? We have above 12 measurements per year times 29 years. So we don’t need ARMA or other BS we can simply subtract the data. I put the numbers in a spreadsheet and calculated the difference between RSS and GISS, RSS and UAH and UAH and GISS. With 348 measurments for each type of instrument I was able to get a very good estimate of standard deviation of the actual measurements. Again, no ARMA, just using the difference between the graphs.
GISS – RSS one sigma 0.099 Two sigma 0.198
RSS-UAH one sigma 0.101 Two sigma 0.202
GISS-UAH one sigma 0.058 Two sigma 0.116
These are actual numbers and are substantially lower than the estimated two sigma by Tamino but still bigger than the 0.1 C per decade although the two sigma GISS – UAH is within a 90% confidence interval already!
This isn’t the end though. Tamino ended his discussion there implying shenanigans and other things of those who see a trend.
Both of our standard deviation calcs are for a SINGLE measurement NOT a trend.
This is a big screw up. How can a self proclaimed statistical expert miss this, it’s beyond me. Anyway, none of us is universally right every day but most hold their tongue rather than post a big boner on the internet. Well most scientists realize that when you take more than one measurement of a value you improve the accuracy. So being a non-genius, I used R to calculate what the statistical certainty of the slope is when taken over 10 year trends. Thanks again to Steve McIntyre for pointing me to this software. I don’t love it but it is convenient.
t=read.csv(”c:/agw/giss data/10 year variation.csv”, header=FALSE)
x = (1:length(t[,1]))
y=t[,1]
a=gls(y ~x)
confint(a)
confint(a)[2,1]-confint(a)[2,2]
y=t[,2]
a=gls(y ~x)
confint(a)
confint(a)[2,1]-confint(a)[2,2]
y=t[,3]
a=gls(y ~x)
confint(a)
confint(a)[2,1]-confint(a)[2,2]
What this script does is load the difference files i.e. GISS-UAH, fits a line to them and presents a number for the statistical confidence interval of the slope coefficient at 95 percent confidence which is about two sigma. The confidence of the slope of the trend is as follows
GISS – RSS Two sigma 0.00108 DegC/year
RSS-UAH Two sigma 0.001068 DegC/year
GISS-UAH Two sigma 0.0005154 DegC/year
Despite a standard deviation of .02 We have a twenty times more accurate slope measurement of 0.001degC/year !
Conclusions
1. We can say with a high degree of certainty that we know the trend of temperature for any ten year plot to within .01 degC/decade.
2. We can say that temperatures have dropped this past decade, just as our eyes looking at the graphs had already told us.
3. We can also say that Tamino owes a few more apologies.
He and Real Climate still don’t let me post on their blogs!
I wonder why?
Tamino has a graph at his own site on this subject from earlier this year. It uses a running mean of ten years. It is obvious from his graph that his next data point (when 2008 is complete) will show significant cooling. The very warm year of 1998 will come of the average and the cool year of 2008 will come on. It will happen as soon as the December temperatures are out. If he has any intellectual honesty, he will have to admit that significant cooling has occured at least by his definition
Several things about your temperature measurments.
Once measured you will never increase your accuracy.
By computing averages of multiple measurements you may very well increase your confidence level of where the actual peak of the normal distribution bell curve of measurement accuracy is and your difference from it your accuracy is still what it is.
It is also interesting to note that all these single measurements you cite are actually averages of multiple measurements. Not only that but the GISS has been adjusted by our pal Herr Hanson so it is a candidate for being tossed out as unreliable.
Among the technologies used to measure temperature the old mercury thermometer is one of the more accurate ones for the range of temperature that we are most interested in.
I also wonder about the graph labled May 1997 to Current.
How come there are multiple years 2007, 2006, 2004 and so forth but poor little 2005 only gets one mention. I think some tic marks on the horizontal axis would be extremely helpful.
John Philip:
You are correct that the 120-point trends are positive. It is also true that for HadCrut, RSS, and UAH, this positive trend flattens, and even goes negative, if extended back to 1997. This, of course, all has to do with arbitrary starting points that impact the slope of the line. The particular chart that Jeff cites is the chart that was put together precisely to show exactly how far back in the data to go without seeing a warming trend. That doesn’t mean there can’t be a warming trend shown for shorter (in this example, 120-month) periods.
In Tamino’s post, he muses philisophical about what the writer of the article meant by “this decade.” I think he mistakenly assumed that “this decade” starts at the year 2000 in his first analysis. I am guessing that the author began this decade in 2001. And if so, it makes sense, since every temperature measure, including GISS and NCDC data shows a negative trend line since the beginning of 2001. I’ve posted those charts in the past. I don’t specifically show charts for HadCrut, RSS, and UAH starting in January 2001, but my spreadsheets verify that these trends are negative.
Steve in SC: Well, there are tickmarks at the zero anomaly. Sorry about 2005 getting dissed… Excel decided for me how the points would be spaced. I suppose I could include month for a better reference point.
Oh, and since my site is referenced as a link on the side, but this was originally posted at Jeff’s site, I will shamelessly provide the link. 🙂
http://digitaldiatribes.wordpress.com
I calculated the trend per decade awhile ago using the Hadley Centre monthly temperature dataset going back to 1850. I started the analysis in Jan. 1850 – then Feb 1850, March 1850 etc. etc. all the way up to the most recent month.
The trend per decade depends on when one starts the measurement and there is a definitive trend in that trend.
[The warming climate models predict 0.2C per decade more-or-less since CO2 started rising at the modern rate – it really should apply starting in 1850 because the logarithmic relationship of GHGs to temperature means temps should have increased pretty close to the 0.2C per decade over the entire period but they often like to pretend it didn’t really kick off until very modern times but this is not accurate – it is simple math afterall – CO2 up – temps up on a logarithmic basis.]
But …
If one starts measuring in 1850, the trend is only 0.04C per decade.
The trend rises slowly so that if you start measuring in 1920, the trend is about 0.07C per decade.
By 1940, the trend is 0.08C, by 1960 the trend is 0.14C per decade, by 1970 we are at 0.17C per decade and by 1992, the magic 0.2C per decade is reached.
Then the trend starts falling precipitously, so that if one starts measuring in 1997, the trend per decade is 0.0C.
From 2002, we are at -0.2C per decade and a scary -0.7C per decade is reached if you start measuring in 2005.
The biggest cause of these varying trends is, in fact, the PDO and El Ninos. There were so many El Ninos in the 1986 to 2006 period that the trendline gets skewed upward.
If you take the PDO impact/changes out of the equation, the trend per decade is a fairly stable 0.08C per decade over most of the period, less than half of the predictions of the climate models.
Those are tiny things. I thought it was just a hairy line to emphasize the zero line.
You are making me get out the bifocals now.
I have to follow up Steve real quick and point out that 1998 also only gets one year mark. It goes: 1997 1997 1998 1999 1999…. I have no idea if that matters, but just to say.
(follow-up to my last posting): as does 2001 while we are at it!
Mr Steve in SC asked (18:32:08) :
“I also wonder about the graph labeled May 1997 to Current.
How come there are multiple years 2007, 2006, 2004 and so forth but poor little 2005 only gets one mention.”
2005 is when I had my first heart attack and is, therefore, treated with particular caution.
(A word from one who knows, if you’re thinking of having a heart attack, think again; there’s a lot of ouch involved.)
Tamino is tightly linked to both Mann and Josh Halpern aka “Eli Rabbit.”
REPLY: More than that, he also has a paper out with Hansen, Gavin et al of RealClimate. He’s in the employ of big nocarbon -Anthony
Ah, you uncovered the man behind the curtain. I would love to narrow it down further.
That explains a lot.
I am curious because I read that he recently stated his professional expertise in statistics on real climate. How expert can he be to miss such easy points as above?
REPLY: here is his paper with the RC crew and dendro-mann
http://www.jamstec.go.jp/frcgc/research/d5/jdannan/comment_on_schwartz.pdf
– Anthony
Tamino’s been bought off? Oh boy, whatta surprise!
Isn’t that the group of people who think exaggerating and falsifying data in order to get there point across is O.K.
“year drop in temperature is not statistically significant,”
Note to Tamino: If you can acurately measure the change, it is significant….
Bjorn Lomborg? a denialist? Is he serious? I guess a denialist is anyone who does not agree with Tamino?
Re: “He [Tamino] and Real Climate still don’t let me post on their blogs!”
Why? Because Real Climate is actually Faux Climate and is staffed by folks who cannot stand to be questioned or challenged and Tamino is a simply clown with similar fears.
Without AGW predominance, hysteria, pseudoscience, and outright junk science these folks would be out of a job. Anyone who legitimately questions the AGW hypothesis (it does not merit being called a theory, imho) threatens their funding and standing.
Re:
Mike C (15:44:07) :
This guy is a politically motivated nobody, why even waste your time with him?
REPLY: Funny, he says the same thing about me. 😉
– Anthony
Funny, an anonymous blogger who inserts distinctively political ad hominem attacks into his writing and who is by intent and effect an anonymous nobody considers Anthony a politically motivated nobody.
Somebody is looking quite silly. No wonder “Tamino” hides his identity from his readers, peers, and colleagues.
Agree with David just as most of us don’t even bother to look at GISS data re manipulation of data ect..for about a year now maybe its time no attention whatsoever should be given to these folks re: science only otherwise… I’m sure they are nice guys LOL. I think they are digging their own climate grave quite nicely they don’t need any help?
I believe that Obama and McCain are confidant that AGW is real. If these numbers are not reviewed and claims debunked we will all be paying carbon credits to Gore, Hansen, Mann, Tamino and to many others. We may be paying in any case, that is how successful the AGW propaganda machine has been.
“He and Real Climate still don’t let me post on their blogs!
I wonder why?”
Just this single fact is all I need to know who are right or who are wrong.
Infidels are not allowd in their church.
I have encountered this problem also, getting posts deleted on AGW bloggs (not CA though) or blocked when I started to point out that real world data do not support AGW and linked to the actual data.
Aren’t you all tired of this seemingly never-ending cherry picking of 1998? Fortunatelyn 2009 is coming so that skeptics will have to refer to a 11-year trend to “prove” temperatures are decreasing – then I’ll come back with the 10-year average.
First, let me say that having followed this site for a long time, I’m pretty convinced that GW isn’t happening. But…
The statistics in this post are wrong. Jeff Id has confused measurement noise (which he doesn’t really estimate 100% correctly – rather he uses the difference in different measurement series as a, probably reasonable, proxy) with weather fluctuations.
Jeff correctly points out that the measurement error is probably very small. However, the accuracy of a trend line isn’t based on that alone, but also weather fluctuations about the trend (which are not due to noise, but instead are real changes that don’t conform to a trend). So in talking about the “significance” of a slope, what we’re really talking about is how adequate a straight line is as a description of the weather changes.
I think it’s fair to say that eyeballing the graphs, you’d be hesitant about fitting a straight line to them, either to show global cooling or to show global warming.
In any case, what Tamino really showed was that there is no statistically significant warming trend over the decade, and only one of the three series shows any evidence of warming at all. Which strikes me as agreeing with the general attitude of this website, no matter how he tries to spin it.
For this calc we only need the variation between measurements so I took the means of each 30yr trend and offset the graphs to have equal mean.
Got it, thanks.
I am still unsure, though how subtracting e.g. UAH from GISS anomalies gives a measurement of ‘noise’? They are, after all, measuring different physical quantities – the tropospheric and surface temperatures respectively. One would expect a close, but not exact correlation – for example, the troposphere seems to be more sensitive to ENSO events, rising more in an El Nino, cooling more in a La Nina. The amount of this difference is interesting but I am unclear as to how it translates into an uncertainty value for the slope,
Similarly, the RSS and UAH use the same raw MSU data and process it differently to get the atmospheric temperature. Subtracting one from the other highlights these different results but I am not sure how it is a metric of noise in the original measurements?
Tamino (and me) calculate the trend for the last 120 months at +0.11C but with a large uncertainty, meaning that the actual trend may be substantially different. Your assertion is that We can say that temperatures have dropped this past decade, just as our eyes looking at the graphs had already told us.. It is not clear from your method above how the positive but uncertain trend is transformed into a cooling trend. Could you expand?
Tamino w.r.t. denialists:
A perfect example of the pot calling the white appliances black.
Jeff Id:
I don’t get this. You are looking at the difference between the measurements of 3 independent methods.
Quote: “What this script does is load the difference files i.e. GISS-UAH, fits a line to them and presents a number for the statistical confidence interval of the slope coefficient at 95 percent confidence which is about two sigma.”
Well done. You have showed that there is a trend between the measurements.