(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: The Hockey Stick graph -- the foundation of global warming theory -- has been shown to be scientifically invalid, perhaps even a fraud.
Answer: The first order of business here is to correct the mischaracterization of this single paleoclimate study as the "foundation" of global warming theory.
What's going on today is understood via study of today's data and today's best scientific theories. Reconstructions of past temperatures are about, well, the past. Study of the past can be informative for scientists, but it is not explanatory of the present nor is it predictive of the future. The scientific foundation of global warming theory contains much more than a few tree-rings and the temperature during the Medieval Warm Period.
RealClimate has an interesting article about what it would mean for today's climate theories if the MWP had indeed been warmer than today.
Now, about that pesky bit of sporting equipment ...
The infamous "Hockey Stick" graph was featured prominently in the IPCC TAR Summary for Policymakers. It was important in that it cast serious doubt on the notion both of a global Medieval Warm Period warmer than the 20th century and of a global Little Ice Age, both long-time (cautiously) accepted features of the last 1,000 years of climate history. It seems these periods were regional, not globally synchronized -- though the LIA seems to have been more widely experienced.
This caused quite an uproar in the skeptic community, not least because of its visual efficacy. Two Canadians, an economist and a petroleum geologist, took it upon themselves to verify this proxy reconstruction by getting the data and examining the methodology for themselves. They found errors in the description published in Nature of the data used -- errors that prevented them from duplicating the study. Mann et al., the hockey stick's creators, published a correction in Nature, noting where the description did not match what had actually been done. The Canadians, McIntyre and McKitrick, then published a paper purporting to uncover serious methodological flaws and problems with data sets used.
Everything from this point on is hotly disputed and highly technical.
All the claims made by M&M have been rebutted in detail by many other climatologists; M&M insist they are completely in error. All of it fits nicely with the expectations of both sides of the global warming issue, both the conspiracy theorists and the champions of peer review.
The rebuttals have been objected to and the objections denied and the denials rejected. The specific issues are highly technical and require considerable time and energy to fully understand. Steve McIntyre has a website devoted to his continued probe of this study and Michael Mann is a contributor to RealClimate, which consumes considerable web space refuting his attacks.
In short, M&M raise many specific and technical objections, and climate scientists seem pretty unified in denying the charges. To my knowledge, the worst indictment from the climate science community came from a study led by Hans Von Storch that concluded M&M was right about a particular criticism of methodology, but that correcting it did not change the study results.
If you want to evaluate the issue for yourself, and do it fairly, you must read the copious material at the sites mentioned above. You must also be prepared to dig into dendrochronology and statistical analysis.
Where does that leave the rest of us -- you know, the ones with lives?
I confess immediately that the technical issues are over my head. I don't know PCA from R^2 from a hole in the ground. But the most critical point to remember, if you are concerned about this for its impact on the validity of AGW theory, is that the fight is over a single study, published eight years ago, focused on paleoclimate. It verges on historical minutia. If you feel the study may be tainted, simply discard it.
The fact is, there are dozens of other temperature reconstructions. They tend to show more variability than the original hockey stick (their sticks are not as straight), but they all support the general conclusions the IPCC TAR presented in 2001: late 20th century warming is anomalous in the last one or two thousand years, and the 1990s were likely warmer than any other time in that period.
Here's a superimposition of numerous global, hemispheric, and regional temperature reconstructions for the last 2,000 years, together with an average. References can be found at the bottom of this Global Warming Art link. Regional variations are of course greater than global, so don't be surprised by how wavy some of the lines are.
(Disclosure: one of the reconstructions used in that page is by the same team that did the infamous hockey stick -- but it is not the same study. To the best of my knowledge, M&M have claimed no problems with that one, though they have expressed some concerns that span the entire field of dendrochronology).
Does the 20th century stand out?
Recently the National Academy of Science in the U.S. did a report on the hockey stick study and found it "plausible," though more uncertain the farther back in time it went. But then, true to form for this debate, another report commissioned by another Senate committee came out right afterwards and condemned it. Sigh.
I have read as much about this controversy as I ever intend to, and come to the firm conviction that I don't have the technical background and/or time required to make a scientific judgment on the issue one way or another. I suspect 95% of the people arguing about this have chosen their position ideologically and won't be able to explain the merits of the various arguments.
So while in my mind MBH are in no way guilty of fraud or incompetence (many of the accusations do go that far), judgment of their research must be approached in reverse: given reason to doubt, I will reject it until it is proven to me that the criticisms are invalid. I can't decide for myself until I devote the required time to both the statistical background and the technical details of M&M vs MBH98. That isn't going to happen!
So where does that leave me and (I suspect) most of you?
Well, it leaves me with dozens of other proxy reconstructions, some by the same team or involving some of its members, some by completely different people, some using tree rings, some using corals, some using stalagmites, some using borehole measurements -- all supporting the same general conclusion. That general conclusion is what's important to me, not whether or not one Bristlecone pine was or was not included correctly in a single eight-year-old study.
Although each of the temperature reconstructions are different (due to differing calibration methods and data used), they all show some similar patterns of temperature change over the last several centuries. Most striking is the fact that each record reveals that the 20th century is the warmest of the entire record, and that warming was most dramatic after 1920.
End of story.
To conclude where I started: study of the past can be informative for scientists, but it is not explanatory of the present, nor is it predictive of the future. The science of global warming is rooted in what we know about today.
Now, can we all get off of the hockey rink and back into the lab?
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caniscandida Posted 9:51 am
17 Dec 2006
Your use of "predictive" in this post on the "hockey stick" graph, however reasonable it may be in climate science, strikes me as a bit too defensive, over against serious attempts to "predict," with greater or lesser certainty, in the several historical disciplines. E.g.:
History. Where is Iraq going to go next? Plainly, there is no way to predict that with much certainty. Nevertheless, it is reasonable to think that some predictions are more reliable than others, if they take fully into account such historical data as the major schism between Sunni and Shia in the third generation of Islam, the artificial creation of "Iraq" out of three distinct Ottoman provinces following WWI, Saddam Hussein's favoring of his own Sunni Arabs and his persecution of Sunni Kurds and Shiite Arabs, and the millennia-long contentions between Mesopotamians and the peoples of the Iranian Plateau.
Biology. Why do species go extinct? The pressures on the grey wolf, anthropogenic, are well documented, so we understand well enough why it finally disappeared from the Lower 48 around the mid 20th century. If the bison had similarly disappeared, the reasons would have been clear enough. The near disappearance of the California condor is a bit harder to understand, but not by much. Same with the ivory-billed woodpecker, so that its alleged re-appearance a couple of years ago in the wetlands of eastern Arkansas was not inconceivable. Hence, we have a very good understanding of how environmental pressures can endanger the continuing viability of species. The "practical" extinction of the Baiji was quite predictable, and similarly the extinction of the northern population of the African white rhino is predictable. The well-documented fate of the passenger pigeon, so incredibly numerous in the early 1800s and then extinct within a century, was a shock; but it turns out its life cycle required breeding in continent-sized populations, and the reduction to merely island-sized populations could not be endured. So, its extinction is related to a great deal that we have learned about "island ecology," and therefore has been instructive to biologists in predicting the grave dangers faced by animal and plant species whose original range has been chopped up by human development and habitat destruction into several "islands."
Paleontology. Why do some lineages thrive and others fail? It is interesting that during the Triassic Period, both the first mammals and the first dinosaurs appeared, from already long-distinct reptilian lineages. If mammals are supposed to be such a superior life-form, then why did they remain in the shadows for the next 170 million years, while dinosaurs became the dominant terrestrial taxa? A suggestion I like, made by the British paleontologist David Norman, is that during the Triassic, all the continents happened to be in close proximity, forming the super-continent known as Pangaea. Climate conditions were likely to have been hot and arid: and that would have suited the basic diapsid poikilothermic metabolism of the dinosaurs' archosaur ancestors much better than the homoiothermic metabolism of the mammals' synapsid ancestors. Hence, if higher temperatures and aridification establish themselves as a normal direction of climate, whether regional or global, we might predict both the extinction of many "warm-blooded" terrestrial vertebrates, and the diversification of the "cold-blooded" reptiles, both anapsid turtles, and contemporary diapsids: lizards, snakes, crocodilians.
Medicine. Can a sickness be prevented? Can a sickness be cured? Can a particular patient be diagnosed with a particular sickness? In this (partly) historical discipline above all, predictability is of supreme importance. The use of statistics and probability -- i.e., the collection and interpretation of data from the past -- is fundamental, both for diagnosis and for preventive care. To say nothing of the importance of "family medical history" as a diagnostic tool.
My suspicion is, you all in climate science would like to be able to make reasonable predictions. (Certainly, the meteorologists have been much mocked and abused by the misunderstanding public for a very long time. "They said it was going to be a major hurricane, so I got out of town, and it turned out to be barely a drizzle!"; "They were predicting a blizzard, I was expecting a day off from school, I did not finish my essay on 'The Scarlet Letter,' and all we got was a little dusting!"; "Forecasting the weather is very simple: If I take my umbrella, it does not rain; if I do not take it, it rains.") But you realize that your ability to explain past data is still too weak to allow you with confidence to predict what lies over the horizon.
Oh well. Hang in there, I have confidence at least that you will get it before long. Not that civilization has too many years left ... : )
Chickens are our cousins!
So are other sensitive animals!
Enough is enough!
No more factory farms!
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Coby Beck Posted 2:19 pm
17 Dec 2006
http://gristmill.grist.org/story/2006/11/19/231018/09
The major obstacles in explaining past climate have to do with the availability of data, or rather lack of. Today's ocean-atmosphere system is so much better measured and monitored than any time in the past that uncertainty about the past says nothing about how well we understand what is going on today.
Invent a clever saying, and your name will live forever!
-- Anonymous
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caniscandida Posted 4:30 pm
17 Dec 2006
In the November post to which you referred me, you wrote this clause: "although we are far from that elusive Perfect Understanding (tm)." Why the capital P and U? And what does "tm" mean?
Chickens are our cousins!
So are other sensitive animals!
Enough is enough!
No more factory farms!
Permalink
Coby Beck Posted 4:07 am
18 Dec 2006
I think that is pretty revealing of geekiness...here I thought everyone new that! ;)
Thanks for clarifying my misunderstanding of your first comment.
Invent a clever saying, and your name will live forever!
-- Anonymous
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willa Posted 8:20 am
18 Dec 2006
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PossumHunter69 Posted 9:01 pm
19 May 2008
The original graph was published in two papers by Mann, Bradley and Hughes (1998, 1999). It purports to show globally averaged temperature anomalies for the Northern Hemisphere for the years 1000 to 1998. Since widespread thermometer measurements are only available since 1860, most of the graph consists of averaged "proxy" measurements, based on tree rings, sediments, corals, ice cores and other indicators of past temperature change. The supposed 95% accuracy is shown in the graph, so that one can deduce that the temperature in 1998 was above previous levels, to that level of probability.
This graph contradicted the opinions expressed in the first IPCC report (Houghton et al. 1990) which claimed that there were higher global temperatures than those shown today during the "medieval warm period" from about 1100 to 1250 AD and that there was a "little ice age" from about 1550 to 1700 AD. The opinion was expressed that the temperature rise shown from 1870 to 1940 may have been a delayed recovery from this Little Ice Age.
Soon and Baliunas (2003a, 2003b) gathered together many "proxies" and listed them. They concluded, firstly, that the coverage of data, even for the Northern Hemisphere, was not sufficiently representative to justify the deriving of an "average" which could be considered reliable. Their second conclusion was that both the medieval warm period and the little ice age were sufficiently frequent in the observations that they must have existed. Also, there was evidence that temperatures during the medieval warm period were frequently higher than those found today.
Von Storch (2004) questioned the assumptions of "variability" used for proxy measurements in the hockey stick. He showed that the low accuracy of the proxy measurements implies a much larger amount of "noise" which meant much higher figures for inaccuracy.
The most devastating attack on the "hockey stick" comes from papers by McIntyre and McKitrick (2003, 2005). They set out to see whether they could recalculate the Mann/Bradley data and were initially surprised to find that the data were not available and had not even been supplied to the journals publishing the work -- the papers had been published, and believed, without any check on their validity.
After a long period of wrangling they managed to get hold of most of the original data. When they carried out the calculations, however, they found serious errors which, when corrected, changed the whole conclusion that had been attributed to them. They found that they got a higher temperature in the year 1400 than is claimed for today. They found that the shape of the curve had been automatically predetermined. The small amount of actual data before 1550 led to the excessive use, including extrapolation, of several measurements that are not considered reliable by others. Holland (2007) has documented the IPCC's determined resistance to accepting these facts.
Loehle (2007) questioned the reliability of tree-ring measurements, which apply only to summer and are influenced by precipitation. Increased temperature lowers soil moisture and the rings get thinner rather than thicker. When he used all the proxies except tree rings he got a modified record which restored both the medieval warm period, the little ice age, and the lack of "unprecedented" character of recent temperatures.
The recent IPCC Report (Solomon et al. 2007) has abandoned the "Hockey Stick" graph, but they still will not accept any criticism of it.
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