Posted on 01/13/2005 4:20:13 PM PST by 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.
Yelling,
Our discussion has been over a few key questions:
1. Was the Medieval warming period a discernable climate anomaly? Was it global in its extent?
2. Was the LIA (Little Ice Age) a discernable climate anomaly? Was it global in its extent?
3. Is there an observable anomoly in the 20th century that is most extreme? Are recent temperatures the highest in a millenia?
There is no debate that LIA and MWP existed at some level, the debate is whether it is global in extent enough to show in the kind of global or hemispheral reconstruction such as Mann made.
Soon and Baliunas, Climate Research Vol 23:89-110, 2003, ask and answer the 3 questions under discussion here directly, with a number of studies from around the world.
http://guisun3.gkss.de/G/Mitarbeiter/storch/pdf/soon+baliunas.cr.2003.pdf
We could gainsay back and forth, but my own sense, which is what the S+B paper states well and backs with over 130 studies, is this:
1. The MWP (warming period of 800-1300) was a real climactic anomaly and was global in extent.
2. The LIA (little ice age of 1300-1900, particularly at in 17th century) was a real climactic anomaly and was global in extent, with temperatures lower than present day.
3. There has been significant warming in the 19th and 20th centuries, but temperature level is not unique to the past millenium. We cant say with any confidence that recent temperatures are the warmest in 1000 years, or warmer than the MWP.
Having just read S+B, I'd just reference that and call it a day. As a PhD in another field (Comp Sci), I am a layperson with a good BS detector. I've read Mann, M+M, and S+B in the past 3 days. Of the papers, S+B impresses me the most as being clearest, most informative, and easiest to verify. The references I have looked at DO verify what they say; it's solid. The Mann work leaves way too many hidden variables and has a suspect way of merging proxy data; this is exactly what M+M is attacking them on. This lack of reproducibility is IMHO bad way to write papers and do science; that he has defenders attacking M+M is a sad commentary on politics trumping good scientific practice here. Anyway, S+B notes general issues with the concept of merging such data (See S+B on page p. 104); the global climate is not a homogeneous entity but a merging of regional climates. Better to take the timelines as individual representations for a regional or local climate. This reduces biasing errors that occurs with wieghting of different proxies.
It also puts in context these other papers that constitute those regional data points, which frankly are rabbit trails in our discussion ...
"The abstract to this paper says: “The results show that over the past 500 years, the investigated areas have on average warmed 1 K, with more than half of the warming occurring in the 20th century alone, and 70–80% in the 19th and 20th centuries taken together.” That sounds pretty clear to me and it would see that the borehole reconstruction in Russia does not support your claim that they put “Mann's work and his easy-to-munge-into-your-preconceived-conclusions-PCA to shame.” (your words)
----
This is consistent with the LIA hypothesis and other studies that show cooler temperatures in 15th-18th century (LIA) and warmer trend in 19th and 20th.
This borehole tells us well what happened to temperature (give or take some error margin in measurement) in this region. Climate changes (eg jet stream, humidity change etc.) may make a region warmer even if the globe is cooling, but it's a data point. (viz. your Keigwin cite.)
Collating the regional pictures is the best way to get a global picture, which is what S+B did. Of the over 100 studies that covered the timescales in question, only a tiny fraction (less than 5%) were inconsistent with the hypothesis of LIA and MWP. On the other hand, the majority of studies and were NOT consistent with the hypothesis that 20th century temperatures were the highest in 1000 years.
As abstract of S+B states, "Across the world, many records revealt that the 20th century is probably not the warmest nor a uniquely extreme climatic period of the last millenium."
... this does not btw invalidate global warming as a hypothesis or invalidate that humans can impact climate, it just invalidates the incorrect extrapolation of Mann's work into the non-error-bar'd 'hockey stick' as unfounded speculation.
As I said, I'll leave it at that: LIA and MWP have more climate science and studies to back them up than the 'hockey stick'.
Since S+B are stating what I've pretty much concluded independently, I'll let that be the 'authority' on my side and end it. I know its had its share of controversy, due to the politicization of this area ...
http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000219scientists_and_the_p.html
... but we wont resolve that here anyway.
"Moving on the second paper you used from Daly’s selection. In it, the paper shows a decrease in SST of 3 – 4 degrees as you state. However if you read the paper (instead of assuming that it means a decrease in global temperature) you find that it also is related to current patterns"
To be clear, niether I nor Daly would think that one data point (a proxy data no less) would tell you what the global temperature was.
FYI, I got the reference by googling for it.
If a website wants to reference something and showcase it, they'll pop up under the circumstances.
"To begin with, in a previous reply you state: “Your reading comprehension is pretty poor, I must say.” ..
A frustrated comment about you saying these papers dispute LIA, ie, "neither supports the idea that global temperatures were warmer during the MWP or cooler during the LIA."
Whereas the paper itself was saying: "The most recent of these events was the Little Ice Age, which occurred between 1300 to 1850 A.D., when subtropical SSTs were reduced by 3 to 4 C. "
But let's not quibble...
"I am curious why you feel a need to insult anyone who disagrees with you? Do you do this always or is this a special occasion?"
You're a special guy. What can I say.
Press Release on the Soon+Baliunas paper:
http://cfa-www.harvard.edu/press/pr0310.html
Release No.: 03-10
For Release: March 31, 2003
20th Century Climate Not So Hot
Cambridge, MA - A review of more than 200 climate studies led by researchers at the Harvard-Smithsonian Center for Astrophysics has determined that the 20th century is neither the warmest century nor the century with the most extreme weather of the past 1000 years. The review also confirmed that the Medieval Warm Period of 800 to 1300 A.D. and the Little Ice Age of 1300 to 1900 A.D. were worldwide phenomena not limited to the European and North American continents. While 20th century temperatures are much higher than in the Little Ice Age period, many parts of the world show the medieval warmth to be greater than that of the 20th century.
Smithsonian astronomers Willie Soon and Sallie Baliunas, with co-authors Craig Idso and Sherwood Idso (Center for the Study of Carbon Dioxide and Global Change) and David Legates (Center for Climatic Research, University of Delaware), compiled and examined results from more than 240 research papers published by thousands of researchers over the past four decades. Their report, covering a multitude of geophysical and biological climate indicators, provides a detailed look at climate changes that occurred in different regions around the world over the last 1000 years.
"Many true research advances in reconstructing ancient climates have occurred over the past two decades," Soon says, "so we felt it was time to pull together a large sample of recent studies from the last 5-10 years and look for patterns of variability and change. In fact, clear patterns did emerge showing that regions worldwide experienced the highs of the Medieval Warm Period and lows of the Little Ice Age, and that 20th century temperatures are generally cooler than during the medieval warmth."
Soon and his colleagues concluded that the 20th century is neither the warmest century over the last 1000 years, nor is it the most extreme. Their findings about the pattern of historical climate variations will help make computer climate models simulate both natural and man-made changes more accurately, and lead to better climate forecasts especially on local and regional levels. This is especially true in simulations on timescales ranging from several decades to a century.
Historical Cold, Warm Periods Verified
Studying climate change is challenging for a number of reasons, not the least of which is the bewildering variety of climate indicators - all sensitive to different climatic variables, and each operating on slightly overlapping yet distinct scales of space and time. For example, tree ring studies can yield yearly records of temperature and precipitation trends, while glacier ice cores record those variables over longer time scales of several decades to a century.
Soon, Baliunas and colleagues analyzed numerous climate indicators including: borehole data; cultural data; glacier advances or retreats; geomorphology; isotopic analysis from lake sediments or ice cores, tree or peat celluloses (carbohydrates), corals, stalagmite or biological fossils; net ice accumulation rate, including dust or chemical counts; lake fossils and sediments; river sediments; melt layers in ice cores; phenological (recurring natural phenomena in relation to climate) and paleontological fossils; pollen; seafloor sediments; luminescent analysis; tree ring growth, including either ring width or maximum late-wood density; and shifting tree line positions plus tree stumps in lakes, marshes and streams.
"Like forensic detectives, we assembled these series of clues in order to answer a specific question about local and regional climate change: Is there evidence for notable climatic anomalies during particular time periods over the past 1000 years?" Soon says. "The cumulative evidence showed that such anomalies did exist."
The worldwide range of climate records confirmed two significant climate periods in the last thousand years, the Little Ice Age and the Medieval Warm Period. The climatic notion of a Little Ice Age interval from 1300 to1900 A.D. and a Medieval Warm Period from 800 to 1300 A.D. appears to be rather well-confirmed and wide-spread, despite some differences from one region to another as measured by other climatic variables like precipitation, drought cycles, or glacier advances and retreats.
"For a long time, researchers have possessed anecdotal evidence supporting the existence of these climate extremes," Baliunas says. "For example, the Vikings established colonies in Greenland at the beginning of the second millennium that died out several hundred years later when the climate turned colder. And in England, vineyards had flourished during the medieval warmth. Now, we have an accumulation of objective data to back up these cultural indicators."
The different indicators provided clear evidence for a warm period in the Middle Ages. Tree ring summer temperatures showed a warm interval from 950 A.D. to 1100 A.D. in the northern high latitude zones, which corresponds to the "Medieval Warm Period." Another database of tree growth from 14 different locations over 30-70 degrees north latitude showed a similar early warm period. Many parts of the world show the medieval warmth to be greater than that of the 20th century.
The study - funded by NASA, the Air Force Office of Scientific Research, the National Oceanic and Atmospheric Administration, and the American Petroleum Institute - will be published in the Energy and Environment journal. A shorter paper by Soon and Baliunas appeared in the January 31, 2003 issue of the Climate Research journal.
You raise a number of interesting points. However they seem to be based mostly on the Soon and Bilanius paper in Climate Research. While this paper does contain a number of references, they turn out to be the type we were already dealing with. For example they use Keigwin to show that the Sargasso had cooler temperatures during the LIA without mentioning that Keigwin thinks this is due to a shift of currents. And they use deMenocal work to show cooling without noting that this was also due to a shift in currents and more upwelling.
There are a number of problems with this paper. As an example, they present the following in their methodology (this is a direct quote, please check me if you don’t believe it ) “Table 1 and Figs. 1 to 3 summarize the answers to the questions posed here about local climatic anomalies. For Questions (1) and (2), we answered ‘Yes’ if the proxy record showed a period longer than 50 yr of cooling, wetness or dryness during the Little Ice Age, and similarly for a period of 50 yr or longer for warming, wetness or dryness during the Medieval Warm Period.”
Read that again!!!!!!!! So if the record is warm OR wet OR dry it supports a warm spell. And if the record is cold OR wet OR dry it supports a cold spell. Consequently any change in precipitation (wet or dry) can support either warm or cold. Add to that the fact that they did not try to establish the magnitude of either warming or cooling. Not surprising this paper did create a lot of stir in the field at the time.
However this was not for the politics but for the bad science. In fact, the Publishers of Climate Reaearch (the journal who published this) had to print a retraction that says:
“Major conclusions of Soon & Baliunas are: ‘Across the world, many records reveal that the 20th century is probably not the warmest nor a uniquely extreme climatic period of the last millenium.’ (p. 89) and ‘Overall, the 20th century does not contain the warmest anomaly of the past millennium in most of the proxy records which have been sampled world-wide’ (p. 104). While these statements may be true, the critics point out that they cannot be concluded convincingly from the evidence provided in the paper. CR should have requested appropriate revisions of the manuscript prior to publication.” In other words, it is an opinion with no science to back it up! It is very rare for a publisher to have to do this and it led to a change in the way CR reviews papers.
If you are interested in an overview of the topic I would refer you to this article:
http://w3g.gkss.de/G/Mitarbeiter/storch/CR-problem/Chronicle%20of%20Higher%20Education.030904.pdf
Anyway, in regards to S&B vs Mann, I will be pleased to stick with Mann. S&B’s work is interesting but from it they can conclude nothing!. I can’t see how you can state that it is solid? Mann’s methodology is complex but it is a complex subject and it is far, far less subjective than S&B’s work.
Fair enough. However I contend that it does not show a change in local climate that could be used to support a change in global temperature. It is merely a change in ocean currents. You can argue that the change in currents is caused by a climate change (either up or down, take your pick) but Daly did not do this and I have yet to see anyone make this link.
""I am curious why you feel a need to insult anyone who disagrees with you? Do you do this always or is this a special occasion?"
You're a special guy. What can I say. "
Thanks, I'll accept that as a compliment. I know it is not, but it is probably the closest I will get arguing the science of global warming on this site ;)
"The paper says that there is a change in temperature during the LIA."
" However it is quite clear that this reduction of temperature is due to a change in ocean currents (as discussed above)."
You keep stating this as if it refuted the temperature measurement itself. It doesnt. The same questioning of causes can be asked of every temperature sample. It does point out that a local measurement may be only relevent locally, and may no necessarily reflect global trends, to which I agree.
Now, I've given a number of sources, including the NOAA website, that state and confirm that LIA was a real and persistent global climate anomaly. If you don't think something that well-measured even existed, we'll have to simply disagree.
"Anyway, in regards to S&B vs Mann, I will be pleased to stick with Mann."
Really. Frankly, the more I read about his views and attacks on others, the more I am disgusted by him. The latest article you sent had his diatribe to Congress aginst S+B in it. His behavior confirms that this scientific domain has become a politicized arena where certain orthodoxies will be maintained at the cost of good science and academic freedom.
Feh on that.
I'd like to see a journal retract MBH98 for its errors; until then I won't trust the keepers of the orthodoxy to be playing with a straight deck.
BTW, since the Chronicle of Higher Education is an organ of academic orthodoxy, it is only fair to present a viewpoint that points out what was left out of the reports on the controversy. Note that this was written before M+M were editorially 'destroyed', yet predicted exactly what Mann et al would do to them:
http://mitosyfraudes.8k.com/Calen2/debunk.html
EDMONTON JOURNAL ,12 November 2003
Lorne Gunter, Columnist, Edmonton Journal
Too many scientists have based their research, their reputations and their incomes on the greenhouse theory.
So rather than debate the growing evidence that the greenhouse theory is fundamentally flawed, many greenhouse-believing scientists have begun viciously attacking those who question its conclusions and denouncing any agnostic as a heretic -- especially ones presenting uncomfortably challenging proof.
Witness Willie Soon and Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics. Both are noted solar physicists. Earlier this year, they published an exhaustive study of the climate of the past 1,000 years or so in the journal Climate Research. They examined more studies on historic climate trends -- 240 in all -- than any previous researchers, and concluded the 20th century was not unusually warm. In the past millennium there had been at least one other period when, worldwide, temperatures were as much as 2 C to 3 C warmer than the 1990s.
This was not a particularly startling conclusion. There have been dozens of papers written by geologists identifying a Medieval Warm Period running from about 800 to 1300 AD and a Little Ice Age spanning 1300 to about 1850. Soon and Baliunas merely confirmed that these earlier studies were right.
But Soon and Baliunas were both vehemently attacked. Myths were spread that they had cooked their findings (as good scientists do, they acknowledged in their article the very limitations in their results that have been used to try to discredit them). Three junior editors at the journal that published their study resigned claiming embarrassment that their employer published shoddy research. Then the controversy sucked down the editor-in-chief.
However, when an independent review was conducted of the Soon/Baliunas article, no misrepresentation was found nor any shortcomings with Climate Research's peer-review process. (These latter facts are often left out of news stories on the controversy, though.)
The reason for the hissy fit over Soon/Baliunas is simple though. The pair do not shy from drawing obvious conclusions from their research: if the warming of the 20th century is not unusual, then it is likely natural, meaning the Kyoto accord is an exercise in futility. And even if the warming is not natural, it is not extreme and thus nothing to worry about.
This is a threat to the greenhouse religion. Therefore the pair must be burned at the stake.
The same fate is likely to befall Canadian researchers Steve McIntyre and Ross McKitrick, who have just destroyed the "hockey stick" theory on recent global warming for the British journal Energy & Environment. (Questioned the theory, or called it into doubt might be less-charged wording, but I'll stick with destroyed.)
The "hockey stick" has been among the holiest of holies in the greenhouse priests' liturgy. It purports to show relatively stable climate for the 900 years from 1000 to 1900, then a sharp spike upward from 1900 to today. Its implications for the greenhouse theory are so central that it formed an integral part of the UN Intergovernmental Panel on Climate Change's vaunted 2001 report, the one that claimed to confirm disastrous manmade greenhouse warming.
We have known for a long time that the hockey stick compared apples and oranges -- reconstructed temperatures from 1000 to 1900 (temperatures deduced from studying tree-ring growth and ice cores, et cetera) and measured temperatures from 1900 onward. When the 20th century's temperatures are "reconstructed," they don't show the warming the hockey stick shows.
But what McIntyre/McKitrick also reveal is the data used to craft the hockey stick are based on "collation errors, unjustifiable truncation or extrapolation ... obsolete data, geographical location errors, incorrect calculation ... and other quality control defects." The wrong places, the wrong dates and the wrong numbers were jumbled together to produce the results the authors desired -- that industrial societies are threatening the planet and only global regulation by the UN can save it.
Three "unjustified truncations" were uncovered by McIntyre/McKitrick. Of 112 temperature records used to create the hockey stick, 13 were incorrectly copied down, 18 mismatched the year and temperatures, 19 made unjustifiable extrapolations to cover missing data, 24 contained obsolete data and all 28 that used tree-ring data miscalculated the information obtained by reading the rings. That's a total of 105 records with errors, although some contained multiple errors, so there were more than seven data sets that were error-free, but not many more.
Emperor Kyoto has no clothes. It's time we called him on it.
Then there is this editorial comment, from Prof Legates, on the controversy:
http://eteam.ncpa.org/commentaries/global_warming/082203dl.html
August 22, 2003
By: Dr. Legates, Associate Professor and Director of the Center for Climatic Research at the University of Delaware. He also serves as a Review Editor for the journal Climate Research.
While most of official Washington was captivated with the fight on the Senate floor to pass an energy bill before they left town for their August vacation, a vicious campaign was underway behind the scenes to smear two prominent scientists for pointing out serious flaws in the science behind the theory of human-caused climate change.
The targets were Drs. Willie Soon and Sallie Baliunas, both astrophysicists at Harvard, who were characterized as fringe scientists whose work should be ignored. What did they do to attract such characterizations? They had the audacity to pull back the curtain on the wizard of global warming.
The issue focuses on a paper by Drs. Soon and Baliunas that supports the widely held view that the climate of the last millennium has been quite variable and includes a Medieval Warm Period and subsequent Little Ice Age. This is only controversial because it, and the wider body of scientific literature that exists, directly contradicts recent research by Dr. Michael Mann, a leading global warming proponent. Mann argues global air temperatures have been stable over the last 1,000 years, with the exception of the last 100. It is the 'Mann-made' warming to which Soon and Baliunas have objected.
While most of these arguments are confined to academic discussions that the general public would find less than boring, this fight played out recently in front of the U.S. Senate Committee on the Environment and Public Works (EPW). It has also been echoed in several news accounts from academic journals to the New York Times.
Dr. Mann testified before the Senate committee that his research is the "mainstream view" because it is featured prominently in a chapter of the United Nations Intergovernmental Panel on Climate Change (IPCC) report, of which Dr. Mann was also a lead author. Soon and Baliunas challenged Mann's claim by reviewing the large body of literature that shows his claims to be unsubstantiated and his research to be fatally flawed. In truth, Mann's work is the scientific outlier - the one study that does not fit with the wealth of scientific evidence.
Soon and Baliunas argue that Mann's conclusions rest on a dubious manipulation of data. While many of the problems in Mann's work require scientific expertise to understand, one flaw is so basic that everyone can understand it. Mann and his colleagues compiled a historical climate reconstruction - called the "hockey stick" because of its shape - primarily using tree ring records to infer air temperature trends. Their use of proxy data is not novel, but the methods they used and thus the results, certainly are. For example, Mann and his colleagues simply attached the surface temperature record of the 20th century to the end of the proxy record. This is an apples-to-oranges comparison as air temperature readings are not directly comparable to proxy records. However, putting the two different sets of data together in this way makes a stunning visual display for the average reader.
In addition, in his analysis for the Northern Hemisphere prior to A.D. 1400, Mann uses data from nine locations in addition to statistical summaries derived from data for the western US only. Four of these additional locations are in the Southern Hemisphere, including Tasmania and Patagonia.
The widespread acceptance of this revisionist history was possible because the global warming community was eager to accept the "hockey stick" as proof of human-caused climate change.
If it remained merely a disagreement about science and research methods, there wouldn't be much of a story - or reason for concern. Unfortunately, it turned into a scientific lynching of Soon and Baliunas and anyone associated with them. For example, Dr. Chris de Freitas, the editor of Climate Research that published the paper, was criticized for having failed in his responsibilities of quality control, even though the paper passed an extensive peer-review process and the publisher defended de Freitas' handling of the paper. It was argued de Freitas should be removed from his position simply for having published it. Even Mann, in his Senate testimony, dismissed de Freitas' credentials solely because he "frequently publishes op-ed pieces in newspapers attacking IPCC and attacking [the] Kyoto [protocol]." The Editor-in-Chief of Climate Research declared that Soon and Baliunas should be barred from publishing their work in the future.
Why is all this important? Global warming alarmists would have governments impose significant regulations with tremendous economic implications. The Bush administration is under attack simply for stating that the science is uncertain whether human-induced global warming is occurring. At the same time, scientists that add credence to that assertion are being silenced.
Yet if recent global warming is largely a result of natural climate variability, policies to reduce global warming would be unnecessary, costly and ineffective. Before we are asked to incur the pain, we should better understand whether there would be any gain.
You must not understand my comments. I do not doubt that the cooling takes place. I say that "However it is quite clear that this reduction of temperature is due to a change in ocean currents". So I don't dispute the cooling, but I am questioning the cause. I think we actually agree on this point.
Also, I am very happy to accept that the MWP and LIA did exist. I don't know of anyone who says otherwise. What I object to is poor scientific methodology and biased reporting being introduced into the debate.
I agree, you have presented a number of papers. However I believe I have discussed most (all?) of them and have shown that they do not support the conclusions as presented.
Interesting, do you have a reference or a link to it?
I had Gumbo yesterday. The resulting greenhouse gasses actually made my house very cold - had to sleep alone on the couch.
The bulk of their paper (http://capmag.com/article.asp?ID=478) does not support your claim. Quite simply, they give numerous worldwide examples of warming during the LO and cooling during the LIA.
I didn't see you address the issue of Mann's deducing temperature from ice cores, tree rings, etc for the 1000 to 1900 part of the graph and using measurements for 1900 onwards. I don't think there's anything "complex" about that, just bad science.
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