A guest post by Basil Copeland
Lucia, at rankexploits.com, has been musing over Tilo Reber’s posting of a graph showing flat 11 year trends in the HadCRUT land-ocean global temperature anomaly and the two MSU satellite data sets, UAH and RSS. In answer to the question whether global warming is on an 11 year hiatus, “not quite,” says Lucia. She challenges Tilo’s omission of the GISS data set, because notwithstanding questions about the reliability of GISS, it still shows a positive trend over the 11 year period in question. Unless all the measures show a flat trend, Lucia’s not ready to conclude that global warming has been on an 11 year hiatus.
I understand the desire to look at as many metrics as possible in trying to divine what is going on with globally averaged temperature. I also understand the reasons for questioning the reliability of GISS. What I don’t understand is why the only measure of trend that seems to count is a trend derived from linear regression. William Briggs recently had an interesting post to his blog on the relationship between trends in CO2 and temperature in which he introduced the use of loess lines to track trends that are not represented well by linear regression. Loess refers to a type of locally weighted regression that in effect fits a piecewise linear or quadratic trend through the data, showing how the trend is changing over time. Especially in an environment where the charge of cherry-picking the data — choosing starting and ending points to produce a particular result – is routinely made, loess lines are a relatively robust alternative to simple trend lines from linear regression.
Click for a larger image
Figure 1 fits a loess line through the data for GISS using the same 11 year period used by Tilo Reber (except that I’ve normalized all anomalies in this discussion relative to their 11 year mean to facilitate comparison to a common baseline). The red line is the GISS anomaly for this period, about its mean, and the blue line is the loess line. While it varies up and down over the period in question, I would argue that the overall trend is essentially flat, or even slightly negative: the value of line at the end of the period is slightly lower than at the beginning of the period. What this loess line shows is that a linear regression trend is not a particularly good way to represent the actual trend in the data. Without actually fitting a linear trend line, we can reasonably guess that it will trend upwards, because of the way the loess line is lower in the first half of the period in question, and higher in the second half. Linear regression will fit a positive, but misleading, slope through the data, implying that at the end of the period the GISS is on an upward trend when in fact the trend peaked around 2006 and has since declined.
Click for a larger image
Figure 2 is rainbow of colors comparing all four of the metrics we tend to follow here on WUWT. Not surprisingly, the loess lines of HadCRUT, UAH and RSS all track closely together, while GISS is the odd duck of the lot. So what does this kaleidoscope of colors tell us about whether global warming is has gone on an 11 year hiatus? I think it tells us rather more than even Tilo was claiming. All of the loess lines show a net decline in the trend over the 11 year period in question. It is relatively minor in the case of GISS, but rather pronounced in the case of the other three. Of the other three, the median anomaly at the beginning of the period, as represented by the loess lines, was 0.125; at the end of the period, the median anomaly had dropped to -0.071, for a total decline of 0.196, or almost 0.2C.
Global warming on hiatus? It looks to me like more evidence of global cooling. Will it continue? Neither linear regression nor loess lines can answer that question. But the loess lines certainly warn us to be cautious in naively extrapolating historical trends derived by simple linear regression.
Not even GISS can support the conclusion from the last 11 years of data that global warming continues to march upward in unrelenting fashion.
crosspatch: I expressed that poorly. The better way is: The cosmic ray intensity has been the same at each minimum since 1954.
If Ninas and Ninos cycle into and out of phase with cyclic ocean temperatures, and these ocean temperature phases cycle into and out of phase with sun cycles, and sun activity cycles into and out of busy and quiet cycles, and cosmic ray bombardment has its own cycles from the sun and outer universe sources, it stands to reason that periodically, all things come together to create very hot temperature decades and very cold temperature decades. I keep going back to the pattern created by school bus windshield wipers. They never track together all the time. They cycle into and out of phase with each other. I believe we have experienced true warming, and I believe we are experiencing true cooling. Every farmer in Wallowa County hopes that the warming trend will return, and quickly. But the signs they see are causing concern that cold will once again invade our quiet little corner of Oregon. I will let you know if the bats begin abandoning their babies. If they do, we need to stock up on heating fuel. It will be a mighty cold winter.
Thanks, Basil, for the “Statistics without Tears”. Even the internecine skirmishing (and discussion) is amusing. Looking forward to anything to be teased from the delta in CO2 with Temperature relation from Spencer, Briggs and others. The non-linear complexities are not promising, however. Even more so with any solar relation.
Its such an eclectic mix of commenters here its hard to single any one out for praise but crosspatch‘s Hansen knee-mining might yield profit as a statistical intrigue.
Zeke,
I think Tilo started at 1997:06, not 1997:01, so as to have exactly 11 years of data (132 months) through 2008:05.
Basil
Here’s something that no one can dispute, no matter what method of trend line they use: the 2000s have (at the very least) not warmed progressively like both the 1970s, 1980s and 1990s did. Every one of those decades got warmer as it went along, from beginning to end…not a straight linear progression upwards, but still going up cyclically. This same warming progression has NOT been seen in the 2000s, indicating a much flatter trend. And since 2001, yes, all of the metrics show either a flat or declining trend.
So I think for anyone to think that there is nothing significant about the change in temperature trends over the past decade would be to ignore the facts.
Why can’t we just look at the raw numbers and forget the smoothing and regressions and all the other statistical analysis. Temperature goes up and it goes down. Right now its cooler than it has been for at least a decade, the numbers are there. Applying the smooting, we can, by picking a starting date (convenient temperature to prove our point) show that it is still warming or is cooling slightly. People don’t need to be confused with statistics, most people don’t get the nuances and frankly, both sides can apply analytical tricks to show that their argument is correct. Just in this thread alone, one can look at graphs that prove that it is getting warmer and cooler at the same time.
Imagine the charts above as cold, hard cash, replace the degrees with dollar signs. Then imagine trying to convince your banker that you are not really losing money or conversely convining your tax auditor that you are indeed losing money. Loess lines, linear regression, Markov Chains, T Test, Chi-Squares aren’t going to convince them, only the raw numbers will. Any average person, looking at the red line in Figure 1 would get the impression that it was warm in 1998, it didn’t get any warmer for 9 years and its cooler this last year. No competing trend lines needed, just present the facts.
Leif,
Torture the data until it confesses. Then we will know the truth.
Basil:
That would explain it.
Lucia:
I was responding to the statement that “The IPCC predictions (or scenarios, if you will) are for linear temp increases”, which is only an accurate statement over a reasonably long timeframe (and even than, its not entirely linear). I’ll grant you that we are approaching the point at which we can say that we have diverged significantly from the projected trend, and I admire the analysis you have done on the subject. As I’ve said before, I think that temperature trends over the past six or so years merit a bit of rethinking of the magnitude of modeled natural forcings, though I’m far from convinced that we need to throw the GHG forcing baby out with the bathwater. Regardless, I’m an interested amateur observer on this debate, so forgive any ignorance on my part. It will be interesting to see how everything plays out in the next few years.
Leif, I am not convinced that changes in cosmic rays due to regular solar cycles are themselves enough to cause cool downs of the magnitude we saw with the little ice age though I believe they could be a contributing factor. Solar magnetics would only work to the extent of the cosmic ray density the solar system itself is embedded in. What I mean is that it might play a bigger role when the solar system is crossing the galactic plane and there are more cosmic rays to allow in. An open door doesn’t do much of there is nothing to go through it.
My gut instinct is that the sun is more variable than we think but on long times frames. Something else interesting: I happened look at a graph showing various glaciations yesterday and it seemed to me that the general trend over time was longer glacial periods and shorter interglacial periods. I didn’t measure it, that’s just how it looked to my eye.
John Nicklin,
Any average person, looking at the red line in Figure 1 would get the impression that it was warm in 1998, it didn’t get any warmer for 9 years and its cooler this last year.
Let’s not confuse the issue with common sense, okay? 🙂
Seriously, those are the “facts.” But what can you say, from just those “facts” alone about next year? The next few years? That’s where the “data analysis” comes in. It is messy, inconvenient, and fraught with pitfalls from the ease with with we can torture the data to get it to confess, even to crimes it did not commit. It is a dirty task, but somebody’s got to do it. Or at least be prepared to respond to those who do it, and do it poorly.
I’m the first to admit that these are matters on which reasonable minds can disagree. I have a personal epistemology that borrows from the language of jurisprudence to describe how certain we can be about what we claim to know:
1) Absolutely certain
2) Very likely (“beyond reasonable doubt” )
3) Maybe, maybe not — reasonable minds can differ.
4) Very unlikely (the negative is “beyond reasonable doubt” ).
5) Not a shred (“scintilla” ) of evidence.
Much of what we are debating doesn’t even rise to 2) on my scale of epistemological knowledge, yet we hear all the time that the evidence for CO2 induced AGW is not just “beyond reasonable doubt” but “absolutely certain” (though the words may vary, that’s the sense we’re left with). I get very put off by those who claim to be scientists who say these matters are settled, whether by that they mean “beyond reasonable doubt” or “absolutely certain.” The only credible position to hold is one which acknowledges that these are matters on which reasonable minds may disagree. Only those who are unreasonable deny this.
Basil
Those snarky smileys in 2) and 5) were supposed to be closing parentheses.
Fixed, how to avoid:
(“comment with accidental snark”)
(“comment with extra space at end between close parenthesis” )
“It looks to me like more evidence of global cooling. Will it continue?”
A lot of data (and anecdotes) indicate it will continue to cool. Clearly the 20 years or so of temp stagnation normally would put any unpoliticised scientific theory in a coffin. CO2 as the main driver looks doubtful.
If the solar theory is correct and sunspots remain absent, then it most very likely will get cooler. Otherwise in about 5 years we’ll have to put the solar theory in a coffin too.
What frustrates me as an “interested observer” who doesn’t have a strong statistical background is that, whenever raw data is presented, it seems to me that the long-term trend is that there is no long-term trend. The figures are highly variable and the trend keeps changing – which makes sense, at least from my limited knowledge of weather and climate.
It seems that most of the words bandied about are trying to establish one trend or another, am I off-base to think that there really is no predictable trend and instead we should concentrate mainly on our immediate environment and being prepared for whatever changes might occur, rather than trying to lock ourselves into major changes for somebody or another’s prediction?
I just saw crosspatch’s 9:29 – there’s a lot of talk about crossing the galactic plane, lately. It’s a “thing,” I guess.
The galactic plane is circa 50-60 LY away. That’s kind of close, but it will take a while to get there, 30 million years or so. Obviously we’re not talking a bright dividing line but a gradual change, but in relative terms we’re moving awfully slow and have plenty of time to worry about it.
“What frustrates me as an “interested observer” who doesn’t have a strong statistical background is that, whenever raw data is presented, it seems to me that the long-term trend is that there is no long-term trend.”
Which brings us back to the beginning. Once you strip the entire debate of Climate Change to its essientials one questions arise:
Is the warming of the last 40 years unprecedented?
Would could also ask, “Has it really warmed that much since 1970?”
Since so much of the debate comes down to data sets, trends, the reliability of the data, etc… the debate can be relegated to statistics and statistical analysis. The issues of Climate Models, theoretical physics, solar theory, atmospheric teleconnections can be put aside until we can agree on what the climate of the recent past. If we cannot get the recent trends correct the rest of the debate is futile.
The problem is, in statistics -like other fields- there is more than one way to skin a cat.
Yes, I think waiting to measure all the metrics is a good, conservative approach. Best not to rush ahead and judge this hiatus too quickly, as the data seems somewhat elusive. I doubt that global warming is a relentless march upwards, as you say, but over hundreds of years I don’t think it can be disputed that the earth will warm unremittingly unless we do something to stop this trend. And to check out my CARTOONS click on my name link.
John Nicklin (08:37:55) :
“Imagine the charts above as cold, hard cash, replace the degrees with dollar signs. Then imagine trying to convince your banker that you are not really losing money or conversely convining your tax auditor that you are indeed losing money.”
You mean just like how financial sites usually have things like 30 and 60 day trend lines in stock price charts?
The real answer is that science is more than pretty pictures, it’s all about numbers. Pictures, like anecdotal evidence, can provide good guidance about what to study, but ultimately what we compare are numbers, e.g. average temperature, rate of change, etc. While that opens up a pandora’s box packed with doubt, finger pointing, etc, it has served science better than reading the tea leaves in the raw data.
“Loess lines, linear regression, Markov Chains, T Test, Chi-Squares aren’t going to convince them, only the raw numbers will. Any average person, ”
Sorry, average people don’t come here, only people with a stronger than average interest in climate do. The discussion here is not about what to put on the front page of USA Today, its about what the climate has done and is doing and that requires numerical analysis to pull the signal out of the noise within the raw data. That it comes up with pretty pictures is partly a bonus.
Basil,
What does the raw data tell us about next year or the next 5 or 10 years? Nothing at all. The analyzed, data shown by the trend lines, has no predictive value either.
If the trends, be they Loess or Regression or Rolling Average or what ever, were predictive, they would have predicted the 2008 cooling. All the trend analysis does is tell us what happened in nice smooth lines instead of jagged peaks and troughs.
I know why we apply the tools of analysis but I’m less certain than ever that those tools are useful in conveying a clear picture to average people, the ones without advanced degrees in statistics.
I would also like to see temperature lines represented as real degrees of C rather than anomolies based on a chosen year. I think if people could see that temperatures have gone up or down by a few tenths of a degree in real terms it would be far less scary than seeing a graph that makes a 0.6 degree anomoly look like a massive increase or decrease. All the manipulation tends to obsfucate the real story. Its like making successive photocopies of photocopies of the Mona Lisa.
The more we massage the data, the less clear it is to just plain folks. So Gore and Hansen can trot out their charts and Anthony and Steve Mc. can trot out theirs, both sets of charts can be statistically valid and both could be wrong, at the same time.
moptop:
“how well it jibes with the cosmic ray idea”.
Not just another catchy sign on, ‘eh. Comparing 5/1996-9/1996 minimum at swpc with today’s one must be struck by the ongoing abscence of flares.
Not only part of a solar indictment in Arctic warming; also 85% of TSI, but for increased albedo, falls between the tropics.
Interview Request
Hello Dear and Respected,
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We at TPS are carrying out a new series of interviews with the notable passionate bloggers, writers, and webmasters. In that regard, we would like to interview you, if you don’t mind. Please send us your approval for your interview at my email address “ghazala.khi at gmail.com”, so that I could send you the Interview questions. We would be extremely grateful.
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Ghazala Khan
The Pakistani Spectator
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Ric,
I know that average people don’t come here, maybe they should though. My point is that its the average people who have to be convinced one way or another so they won’t support stupid ideas like carbon cap and trade schemes and biofuels, etc.
Ric,
“You mean just like how financial sites usually have things like 30 and 60 day trend lines in stock price charts?”
What did the market trends look like just before the market crash in 1929? Just before the crash, Irving Fisher said, “Stock prices have reached what looks like a permanently high plateau.”
All I’m saying is that while data analysis can help us understand what is happening or, more appropriately, has happened, that same analysis is a blunt tool for predicting the future, immediate or long term.
[…] individual bloggers have expressed a strong preference for one particular data set or another. Like Atmoz, I prefer not […]
Ghazala Khan from The Pakistani Spectator (TPS)?
Why not Anthony? Seems legit.
AGW alarmists are only going to make life for poor Pakistanis even more difficult.
In the last 80 years there has been an almost straight line rise in CO2 (and esentially the same for the square root of CO2 concentration). If CO2 is the major cause of temperature rise then you would expect the temperature rise to be a straight line rise proportianal to the square root of the CO2 rise. This is not what has occured. This means that other factors are much larger over a 10 to 20 year period and as a result it will probably require another 40 to 60 years before the temperature data will tell us whether CO2 rise is a signifigent concern.
As it stands now I would say CO2 rise may have a small effect on temperature and it is most likely to be less than 2 F (this small change will be mostly benificial)