GLOBAL WARMING BOMBSHELL: Hockeystick Broken

MIT Technology Review ^ | 15 October 2004 | Richard Muller

[neverdem]

A prime piece of evidence linking human activity to climate change turns out to be an artifact of poor mathematics.

Progress in science is sometimes made by great discoveries. But science also advances when we learn that something we believed to be true isn't. When solving a jigsaw puzzle, the solution can sometimes be stymied by the fact that a wrong piece has been wedged in a key place.

In the scientific and political debate over global warming, the latest wrong piece may be the "hockey stick," the famous plot (prominently displayed by the IPCC report, 2001), published by University of Massachusetts geoscientist Michael Mann and colleagues. This plot purports to show that we are now experiencing the warmest climate in a millennium, and that the earth, after remaining cool for centuries during the medieval era, suddenly began to heat up about 100 years ago--just at the time that the burning of coal and oil led to an increase in atmospheric levels of carbon dioxide.

I talked about this at length in my December 2003 column. Unfortunately, discussion of this plot has been so polluted by political and activist frenzy that it is hard to dig into it to reach the science. My earlier column was largely a plea to let science proceed unmolested. Unfortunately, the very importance of the issue has made careful science difficult to pursue.

But now a shock: independent Canadian scientists Stephen McIntyre and Ross McKitrick have uncovered a fundamental mathematical flaw in the computer program that was used to produce the hockey stick. In his original publications of the stick, Mann purported to use a standard method known as principal component analysis, or PCA, to find the dominant features in a set of more than 70 different climate records.

But it wasn't so. McIntyre and McKitrick obtained part of the program that Mann used, and they found serious problems. Not only does the program not do conventional PCA, but also it handles data normalization in a way that can only be described as mistaken.

Now comes the real shocker. This improper normalization procedure tends to emphasize any data that do have the hockey stick shape, and to suppress all data that do not. To demonstrate this effect, McIntyre and McKitrick created some meaningless test data that had, on average, no trends. This method of generating random data is called "Monte Carlo" analysis, after the famous casino, and it is widely used in statistical analysis to test procedures. When McIntyre and McKitrick fed these random data into the Mann procedure, out popped a hockey stick shape!

That discovery hit me like a bombshell, and I suspect it is having the same effect on many others. Suddenly the hockey stick, the poster-child of the global warming community, turns out to be an artifact of poor mathematics. How could it happen? What is going on? Let me digress into a short technical discussion of how this incredible error took place.

In PCA and similar techniques, each of the (in this case, typically 70) different data sets have their averages subtracted (so they have a mean of zero), and then are multiplied by a number to make their average around that mean to be equal to one; in technical jargon, we say that each data set is normalized to zero mean and unit variance. In standard PCA, each data set is normalized over its complete data period; for the global climate data that Mann used to create his hockey stick graph, this was the interval 1400-1980. But the computer program Mann used did not do that. Instead, it forced each data set to have zero mean for the time period 1902-1980, and to match the historical records for this interval. This is the time when the historical temperature is well known, so this procedure does guarantee the most accurate temperature scale. But it completely screws up PCA. PCA is mostly concerned with the data sets that have high variance, and the Mann normalization procedure tends to give very high variance to any data set with a hockey stick shape. (Such data sets have zero mean only over the 1902-1980 period, not over the longer 1400-1980 period.)

The net result: the "principal component" will have a hockey stick shape even if most of the data do not.

McIntyre and McKitrick sent their detailed analysis to Nature magazine for publication, and it was extensively refereed. But their paper was finally rejected. In frustration, McIntyre and McKitrick put the entire record of their submission and the referee reports on a Web page for all to see. If you look, you'll see that McIntyre and McKitrick have found numerous other problems with the Mann analysis. I emphasize the bug in their PCA program simply because it is so blatant and so easy to understand. Apparently, Mann and his colleagues never tested their program with the standard Monte Carlo approach, or they would have discovered the error themselves. Other and different criticisms of the hockey stick are emerging (see, for example, the paper by Hans von Storch and colleagues in the September 30 issue of Science).

Some people may complain that McIntyre and McKitrick did not publish their results in a refereed journal. That is true--but not for lack of trying. Moreover, the paper was refereed--and even better, the referee reports are there for us to read. McIntyre and McKitrick's only failure was in not convincing Nature that the paper was important enough to publish.

How does this bombshell affect what we think about global warming?

It certainly does not negate the threat of a long-term global temperature increase. In fact, McIntyre and McKitrick are careful to point out that it is hard to draw conclusions from these data, even with their corrections. Did medieval global warming take place? Last month the consensus was that it did not; now the correct answer is that nobody really knows. Uncovering errors in the Mann analysis doesn't settle the debate; it just reopens it. We now know less about the history of climate, and its natural fluctuations over century-scale time frames, than we thought we knew.

If you are concerned about global warming (as I am) and think that human-created carbon dioxide may contribute (as I do), then you still should agree that we are much better off having broken the hockey stick. Misinformation can do real harm, because it distorts predictions. Suppose, for example, that future measurements in the years 2005-2015 show a clear and distinct global cooling trend. (It could happen.) If we mistakenly took the hockey stick seriously--that is, if we believed that natural fluctuations in climate are small--then we might conclude (mistakenly) that the cooling could not be a natural occurrence. And that might lead in turn to the mistaken conclusion that global warming predictions are a lot of hooey. If, on the other hand, we reject the hockey stick, and recognize that natural fluctuations can be large, then we will not be misled by a few years of random cooling.

A phony hockey stick is more dangerous than a broken one--if we know it is broken. It is our responsibility as scientists to look at the data in an unbiased way, and draw whatever conclusions follow. When we discover a mistake, we admit it, learn from it, and perhaps discover once again the value of caution.

Richard A. Muller, a 1982 MacArthur Fellow, is a physics professor at the University of California, Berkeley, where he teaches a course called "Physics for Future Presidents." Since 1972, he has been a Jason consultant on U.S. national security.

[Always Right]

He's dead? Oh dear, I was a fan of his 'Still waiting for Greenhouse' site, but now I see that it is gone.

Yes, it was sad to lose a man who did more to combat the propaganda of global warming than anyone. John was a mathematical genius who could cut through the global warming crap as fast as they could put it out, which is saying something. His daughter and a friend were suppose to keep up his site in his honor, but it is just not the same. John Daly was quite the one man show.

[neverdem]

I found this story at www.sepp.org today.

[farmfriend]

Rights, farms, environment ping.
Let me know if you wish to be added or removed from this list.
I don't get offended if you want to be removed.

[WOSG]

here is a 'tell' - Mann now says it's a 'myth' of the hockey stick that it implies temperatures are higher in 20th century than at any time in 1000 years. hmmm, check that with the popular descriptions and scaremongering on global warming.

So M+M tell us Mann is wrong, get rejected by the 'in-crowd' at Nature, and post it for others to see ... and Mann feels the need to post retorts on the web as a way to wage his own PR campaign. I smell defensiveness. As Gomer Pyle would say - "surprise surprise".

[U S Army EOD]

You didn't mention the cultivated fields in Greenland.

[WOSG]

Having read some of the reactions to this work, I'm stuck on a simple point:

The statistics math can be argued to and fro, but ...

Why do they need such complex statistical jiggering to make the point about what the average temperature is?

That seems to be at least one hole in the hockey stick.

Then there is the difficulties of some of the proxy data ...

" Tree rings are created during the growing season, not over an entire year. They tell scientists little or nothing about annual climate. Think of it this way: This year (2000) there was a warm winter and early spring in the northeastern U.S., followed by an unusually cool summer and fall. These events largely are self-cancelling. As a consequence, 2000 will be fairly average. But the tree rings only will record the cool summer and thus give a completely false impression of the full year’s temperature.... To state the obvious, trees grow on land. Because oceans, seas, and lakes inundate 71 percent of the earth, tree rings tell us nothing about maritime climate. This is no small point. Oceans are the primary determinant of climate conditions throughout the world." - John Daly

[WOSG]

Here is the best refutation of the 'hockey stick', going directly to the temperature and proxy data, a more fundamental problem than the statistical methods used:

http://www.greeningearthsociety.org/Articles/2000/hockey.htm

[Straight Vermonter]

kyoto fans will be deeply saddened (but watch them claim it is necessary anyway!)

It is neccessary! How else to limit progress? How else to limit increasing wealth? How else to end the increase in life expectancy? How else to reduce the world's growing food supply etc etc etc?

[neverdem]

Thanks for the link. It supports other articles I've read about sunspot activity and solar radiation. Bookmarked

[Bloody Sam Roberts]

Uncovering errors in the Mann analysis doesn't settle the debate; it just reopens it.

I think the bigger question is, did Mann have any motivation for making the data trend one way versus another? Some bias perhaps?

[Straight Vermonter]

Likewise it was far cooler 400 years ago than is "normal". Samuel Champlain's accounts of what is now the Champlain Valley describe snow on mountain tops in June. Something never seen today. Cortez's account of events around what is today Mexico City include references to frost covered ground in the mornings.

Temps change always have, always will.

Ice Ages & Astronomical Causes
Brief Introduction to the History of Climate
by Richard A. Muller

Origin of the 100 kyr Glacial Cycle

Figure 1-1 Global warming source NOAA

 

Figure 1-2 Climate of the last 2400 years, source "GISP2"

 

 

Figure 1-3 Climate of the last 12,000 years, source "GISP2"

Figure 1-4 Climate of the last 100,000 years, source Greenland ice data

 

Figure 1-5 Climate for the last 420 kyr, from Vostok ice data

 

http://newton.ex.ac.uk/aip/physnews.252.html#1

INTERPLANETARY DUST PARTICLES (IDPs) are deposited on the Earth at the rate of about 10,000 tons per year. Does this have any effect on climate? Scientists at Caltech have found that ancient samples of helium-3 (coming mostly from IDPs) in oceanic sediments exhibit a 100,000-year periodicity. The researchers assert that their data, taken along the Mid-Atlantic Ridge, support a recently enunciated idea that Earth's orbital inclination varies with a 100-kyr period; this notion in turn had been broached as an explanation for a similar periodicity in the succession of ice ages. (K.A. Farley and D.B. Patterson, Nature, 7 December 1995.)
Farley & Patterson 1998, http://www.elsevier.com/gej-ng/10/20/36/33/37/32/abstract.html
Farley http://www.gps.caltech.edu/~farley/
Farley http://www.elsevier.nl/gej-ng/10/18/23/54/21/49/abstract.html

 

http://www.publicaffairs.noaa.gov/pr96/dec96/noaa96-78.html

ABRUPT CLIMATE CHANGE DURING LAST GLACIAL PERIOD COULD BE TIED TO DUST-INDUCED REGIONAL WARMING

Preliminary new evidence suggests that periodic increases in atmospheric dust concentrations during the glacial periods of the last 100,000 years may have resulted in significant regional warming, and that this warming may have triggered the abrupt climatic changes observed in paleoclimate records, according to a scientist at the Commerce Department's National Oceanic and Atmospheric Administration. Current scientific thinking is that the dust concentrations contributed to global cooling.

 

Here Comes the Sun

"Carbon dioxide, the main culprit in the alleged greenhouse-gas warming, is not a "driver" of climate change at all. Indeed, in earlier research Jan Veizer, of the University of Ottawa and one of the co-authors of the GSA Today article, established that rather than forcing climate change, CO2 levels actually lag behind climatic temperatures, suggesting that global warming may cause carbon dioxide rather than the other way around."

***

"Veizer and Shaviv's greatest contribution is their time scale. They have examined the relationship of cosmic rays, solar activity and CO2, and climate change going back through thousands of major and minor coolings and warmings. They found a strong -- very strong -- correlation between cosmic rays, solar activity and climate change, but almost none between carbon dioxide and global temperature increases."

[liberallarry]

Don't be silly.

Mann takes his science seriously and dreads the consequences of global warming. He's countering bad arguments in a way he feels the public can understand.

Specifically, he says MM's statistical analysis is flat out wrong. I can't follow the logic so I don't know whether he's right but it seems his peers support him on the merits.

[Owl558]

You are a top notch FReeper Straight Vermonter. Thanks for the material.

[Straight Vermonter]

I should have credited ancient_geezer who posted that material on an earlier thread.

But thanks all the same!

[Owl558]

"I should have credited ancient_geezer"

You are both doing a service for humanity!!

[ancient_geezer]

 

Oh dear, I was a fan of his 'Still waiting for Greenhouse' site, but now I see that it is gone.

http://www.john-daly.com/

Site is still up an running, lil different URL is all. Daughter is keeps it updated, though nothing comparable to John's passion for the subject.

[Red Sea Swimmer]

"Global Warming" is a lie perpetrated to further the myopic, evil aims of a few groups of people. These groups are masters of manipulation. If there was an Olympic Sport of Manipulation they would hold all of the world records and would scoop the pool in Bronze, Silver and Gold medals.

[E.G.C.]

BTTT!!!!!!

[E.G.C.]

BTTT!!!!!!

[PGalt]

GREAT FReeper research/links bump!