Doug L. Hoffman
Friday, Dec 18th, 2009
While climate skeptics have gleefully pointed to the past decade’s lack of temperature rise as proof that global warming is not happening as predicted, climate change activists have claimed that this is just “cherry picking” the data. They point to their complex and error prone general circulation models that, after significant re-factoring, are now predicting a stretch of stable temperatures followed by a resurgent global warming onslaught. In a recent paper, a new type of model, based on a test for structural breaks in surface temperature time series, is used to investigate two common claims about global warming. This statistical model predicts no temperature rise until 2050 but the more interesting prediction is what happens between 2050 and 2100.
David R.B. Stockwell and Anthony Cox, in a paper submitted to the International Journal of Forecasting entitled “Structural break models of climatic regime-shifts: claims and forecasts,” have applied advanced statistical analysis to both Australian temperature and rainfall trends and global temperature records from the Hadley Center’s HadCRU3GL dataset. The technique they used is called the Chow test, invented by economist Gregory Chow in 1963. The Chow test is a statistical test of whether the coefficients in two linear regressions on different data sets are equal. In econometrics, the Chow test is commonly used in time series analysis to test for the presence of a structural break.
A structural break appears when an unexpected shift in a time series occurs. Such sudden jumps in a series of measurements can lead to huge forecasting errors and unreliability of a model in general. Stockwell and Cox are the first researchers I know of to apply this econometric technique to temperature and rainfall data (a description of computing the Chow test statistic is available here). They explain their approach in the paper’s abstract:
A Chow test for structural breaks in the surface temperature series is used to investigate two common claims about global warming. Quirk (2009) proposed that the increase in Australian temperature from 1910 to the present was largely confined to a regime-shift in the Pacific Decadal Oscillation (PDO) between 1976 and 1979. The test finds a step change in both Australian and global temperature trends in 1978 (HadCRU3GL), and in Australian rainfall in 1982 with flat temperatures before and after. Easterling & Wehner (2009) claimed that singling out the apparent flatness in global temperature since 1997 is ’cherry picking’ to reinforce an arbitrary point of view. On the contrary, we find evidence for a significant change in the temperature series around 1997, corroborated with evidence of a coincident oceanographic regime-shift. We use the trends between these significant change points to generate a forecast of future global temperature under specific assumptions.
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This reminds me of Asterix and the Soothsayer – the bogus soothsayer’s favourite quote was “this I had forseen” after everything that happened. The peasant villagers were in awe of him!
The only reason the exaggerating warm mongers predict so far out is because no one has evidence to post against their claims.
Today. Who predicted this northern hemisphere frigid events last summer? If they didn’t they need to be ignored for having defective models.
declare Real Climate a Best Religious Blog Weblog Award Finalist for 2009.
The top four vote recipients, in order, were:
1. One Cosmos 253
2. RealClimate 149
It makes sense they predict warming by reason of faith.
What sense has to base anything on HadCRUT? It is like genetic researcher basing its study on Lysenko pseudoscience.
Back to the drawing board and while at it, check the Arctic temperatures record without UHI: http://climexp.knmi.nl/data/icrutem3_hadsst2_0-360E_66-90N_na.png
There’s a lot crystal-balling behind all this. +/- 1 degree C either way over 100 years wouldn’t be noticeable if no one talked about it.
Aaah quick ship a copy off to the Australian government – they keep thinking the earth has a terrible fever and they must tax us all to death to stop it!
All these climate predictions / forecasts are utter crap. What matters is what will happen to the climate in the next 100 years and nobody knows. The Met Office (if honest) can tell you how useless their computer forecasts are for the next 12 months.
I will remain a sceptic until they have proof of AGW and not warm weather events, otherwise I will cite the freezing weather in the USA, Europe, China etc., as a sign of the arrival of a Little Ice Age.
People like Sarah Archdale might be here to tell you all about it: http://www.yorkpress.co.uk/news/4835291.Injured_cyclist_found_unconscious_in_snow/
Ecotretas
I read this a few weeks back. While it seems to have a good outlook, something that bothers me is the durations of future flat/cooling and warming trends. If you look over the past few trends, they had durations of around 30 years, and these guys are looking at 40 and 50+ year trends.
Juraj….i was thinking the same thing. Shouldn’t HadCRUT be tossed out by now in experiments used to predict anything?
yet another model that PROVES nothing
On the Thursday, 10 December 2009 the BBC reported:
“The global average temperature could reach a record high in 2010, according to the UK’s Met Office.”
http://news.bbc.co.uk/2/hi/science/nature/8406839.stm
There they go again! Do these climate tricksters have any sense of shame? It’s their continued failed
predictions that might ultimately falsify AGW.
Henry: “Today. Who predicted this northern hemisphere frigid events last summer?”
I believe Obama’s Science Czar did… back in 1971. He sure knows how to pick ’em!
If i understand this correctly they use a technique usually used in technical analysis of stock charts. I won’t say they’re prediction is better or worse than the ones you would get with an unbiased GCM but it’s a fresh start. Gotta look into that Chow test.
But… but… but… I thought the science was settled! Now I’m confused.
What will the 2 M say to it ;.)
Let’s see if I have this straight: Since the all the previous Climate Change models have now been shown to be fatally flawed we’re using a new model which is based on a test devised by an …
ECONOMIST ?!!
Did everyone else sleep through the past 18 months and miss the great recession?
To paraphrase Gene Siskel, this isn’t scraping the bottom of the barrel, this is digging up the ground underneath the barrel.
So, I could use a random number generator and produce a prediction that is better than the “re-factored” GCM. Actually, I thinks Patrick Michaels showed that this was the case before the re-factoring.
As a note, software developers usually don’t consider it “re-factoring” if the output of code changes. Refactoring generally refers to making code more portable and maintainable.
Slightly OT, but have we reached a tipping point for temp decline acceleration with the increased snow cover? Seems apparent to this untrained eye on Cryosphere that there has been a huge increase in N Hemis. snow cover, including about 1/2 of the British Isles.
Any models have temp predictions that take this into account?
Also, we’re hearing almost nothing current about the arctic ice pack.
Just wondering!
Isn’t this awfully similar to technical analysis in financial trading: statistical models that test well against the past but with uncertain predictive power? As far as I can tell, there is no real hard science (“laws of climate”) within the climate models.
In financial trading, when money managers use the wrong models to deliver suboptimal results, they get fired. Too bad there is no such feedback mechanism for the bad climate models.
Isn’t the stepwise function probably due to poor data?
http://www.theclimateconspiracy.com/?p=180
Anthony, is it at all possible to make some type of chart that shows where all the data comes from, which goes into which data sets, and all of that?
Meh.
And just how good were those econometric models at predicting our present economic melt down?
Look, I am an economist. And there is much about the field that is valid and that I enjoy. But: I make a living from doing what economic theory says it is not possible to do. I “beat the market”. So do a large number of other traders. If computer models of chaotic systems could predict with any skill, you would see a whole bunch of rich economists. Instead what you see is a whole bunch of rich traders (who’s skills are more closely tied to those of gamblers than economists) and a bunch of very poor economists.
FWIW most of the computerized trade models break down for exactly the reason shown in the example above. They are “trend following” models and try to find ever more clever ways to project the trend. They can even work well for long periods of time (for example, I ‘trend followed’ right up to 2008). THEN they break down. Horridly. See 2008-2009 for what that looks like…
Trading is a very different skill set. It is all about following the trend when you have it AND doing very early very fast “inflection detection” when it changes. And chaotic systems DO change, and fast.
IMHO, as a person who trades for a living, 1998 was a “blow off top” in temperatures exactly was we see in stock charts. Now I can’t at all tell you why they both act the same, but I can tell you that I see the same patterns in them. At many tops, you get an unsustainable spike up, then a plummet.
As a trader, catching those inflection points is everything, and that is why 90+% of folks who trade, lose. They win for a while, then miss an inflection, and are wiped out.
That is what I see happening now in the AGW crowd. The inflection happened (IMHO on a 60 year PDO, the 30 year 1/2 cycle has swapped) and they are finding ever more desperate ways to show that their trend following model will start working again Real Soon Now. If they are like most folks, they will continue this behaviour right into the next little ice age.
That they chose to use econometric tools to do this is, to me, confirmation of their error. If you want to be right, use trader tools… I’d use a MACD – moving average convergence divergence. We have about 200 years of decent data, so I’d use a 25 / 12 / 6 years set of simple moving averages for my moving average stack and the usual MACD formula uses a 9 period exponential moving average as the signal line against a 12/26 baseline. Visualizing that (I’ve stared at a million of these, so I can visualize it now even though it will be encrypted Greek to most folks) shows a top inflection. MACD will be screaming down (EMA of 9 years since 2000? Yea, down. While 12/26 period ought to be up tilted rolling into flat). A 25 year SMA will be on top flattening, while a 12 year will be flat and a 6 year will be under it. “SMA stack rolled over”.
And that would be a screaming SELL!! top inflection no doubt about it.
And frankly, I’ll take ‘trader tools’ over “economist tools” any day. One works and makes me money. The other makes pretty pictures and gets you tenure (but don’t ever trade based on it.)
For folks wanting to see what this trader stuff looks like, you can look here:
http://chiefio.wordpress.com/2009/12/22/wsw-monday-december-21-2009/
I’m “due” to make an updated posting of it, but the charts are live charts and you will see what the market looks like today. Down toward the bottom is a link to a description / explanation of the “indicators” that will do a better job than I’ve done in this comment.
Nice model, did they use a ruler and pencil for that graph?
By the way, the Earth will continue to warm after 1000 years pause. There is no way to verify this, but it is what our reliable model(s) predicts.
Nailed it!!!
Global Warming is still ON!