If you do a search at this blog site for 'hockey stick', Google will provide you with about 70 links and the first will link to a question I posted a year ago:
"What is the evidence for the medieval warm period? My understanding is that the Vikings were able to settle Greenland and grow grapes in Canada over several hundreds of years because the climate was significantly warmer. Yet this period is not evident in the famous 'hockey stick' graph."
The Graph
[from BBC News]
The graph was the creation of Dr Michael Mann, et al, and was used by the United Nation's Intergovernmental Panel on Climate Change (IPCC) to conclude in their influential 2001 assessment report that the 1990s was the warmest decade and 1998 the warmest year of the last millenium.
Indeed the 'hockey stick' has emerged as something of an icon for believers in anthropogenic global warming (AGW), while global warming skeptics have dismissed it as shoddy science and another example of 'believers' using models to support a position at odd with the evidence in particular the existence of the medieval warm period.
Now a prominent statistician who is also a Univeristy Professor, Chair of the National Academy of Sciences Committee on Applied and Theoretical Statistics, and a member of the board of the American Statistical Association, has published a rather damning report on the hockey stick. As Paul Williams commented in the thread following my blog post last Friday, "... the hockey stick has just been hit for six"!
Following are some of the conclusions from Dr Edward Wegman as summarized by the US House Committee on Energy and Commerce:
1. Mann et al., misused certain statistical methods in their studies, which inappropriately produce hockey stick
shapes in the temperature history. Wegman’s analysis concludes that Mann’s work cannot support claim that
the1990s were the warmest decade of the millennium.
Report: “Our committee believes that the assessments that the decade of the 1990s was the hottest
decade in a millennium and that 1998 was the hottest year in a millennium cannot be supported by
the MBH98/99 analysis. As mentioned earlier in our background section, tree ring proxies are
typically calibrated to remove low frequency variations. The cycle of Medieval Warm Period and
Little Ice Age that was widely recognized in 1990 has disappeared from the MBH98/99 analyses,
thus making possible the hottest decade/hottest year claim. However, the methodology of
MBH98/99 suppresses this low frequency information. The paucity of data in the more remote past
makes the hottest-in-a-millennium claims essentially unverifiable.”
2. A social network analysis revealed that the small community of paleoclimate researchers appear to review
each other’s work, and reuse many of the same data sets, which calls into question the independence of peerreview and temperature reconstructions.
Report: “It is clear that many of the proxies are re-used in most of the papers. It is not surprising that
the papers would obtain similar results and so cannot really claim to be independent verifications.”
3. Although the researchers rely heavily on statistical methods, they do not seem to be interacting with the
statistical community.
Report: “As statisticians, we were struck by the isolation of communities such as the paleoclimate
community that rely heavily on statistical methods, yet do not seem to be interacting with the
mainstream statistical community. The public policy implications of this debate are financially
staggering and yet apparently no independent statistical expertise was sought or used.”
4. Authors of policy-related science assessments should not assess their own work.
Report: “Especially when massive amounts of public monies and human lives are at stake,
academic work should have a more intense level of scrutiny and review. It is especially the case
that authors of policy-related documents like the IPCC report, Climate Change 2001: The Scientific
Basis, should not be the same people as those that constructed the academic papers.”
5. Policy-related climate science should have a more intense level of scrutiny and review involving statisticians.
Federal research should involve interdisciplinary teams to avoid narrowly focused discipline research.
Report: “With clinical trials for drugs and devices to be approved for human use by the FDA, review
and consultation with statisticians is expected. Indeed, it is standard practice to include statisticians
in the application-for-approval process. We judge this to be a good policy when public health and
also when substantial amounts of monies are involved, for example, when there are major policy
decisions to be made based on statistical assessments. In such cases, evaluation by statisticians
should be standard practice. This evaluation phase should be a mandatory part of all grant
applications and funded accordingly.”
6. Federal research should emphasize fundamental understanding of the mechanisms of climate change, and
should focus on interdisciplinary teams to avoid narrowly focused discipline research.
Report: “While the paleoclimate reconstruction has gathered much publicity because it reinforces a
policy agenda, it does not provide insight and understanding of the physical mechanisms of climate
change… What is needed is deeper understanding of the physical mechanisms of climate change.”
Read the full report here: http://energycommerce.house.gov/108/home/07142006_Wegman_Report.pdf .
Greg - You are absolutely correct here. Some of the things you mention have been touched on in previous discussions however you make some good points.
As far as I am concerned the various proxy studies do show that 20th century warming is unprecendented.
One thing which seems to have escaped all eyes is looking at the graph critically.
The dark 'median' line - the 40 year smoothed - shows a distinct peak or series of peaks in the period pre 1400 - about the time we are talking of the Norse in the western North Atlantic. Just because the peaks are below the line marked '0.0' is not a reason to dismiss them. That line is an anomaly above or below the period 1961-1990 - already over a hundred years into the period of AGW. If you draw the line through, say, an equivalent period in the early 1700's (pre industrial revolution) then the period in concern is warmer than the 'average', but not as warm as now. The '0.0' value would drop by 0.3.
The main things to get from the graph are that the current period is showing a rapid increase in rate of change, as well as a rapid increase in extent. Both are important, and much more important than either independently.
Also, it was nice to see someone else mention that the extent of cleared lands, of bared soil and of 'anthropogenic habitat change' that may be an important causal factor too. No one can deny that we have much more land under production now than at any other time in history - certainly more than would have been needed to feed the (maybe maximum of) 1 billion inhabitants on the planet in the early years of the industrial revolution.
No one has pointed out, either, that there is one system not accounted for here (oceanic CO2 dampening). What we are seeing may be that that system is getting close to capacity, and so the first 100 years or so of released CO2 'filled up' the buffer, and now the problem may get much worse.
As the Hitch Hiker's Guide to the Galaxy says, of dealing with the hagumemnons - 'run away, very fast...'
As a biologist I am a bit skeptical about tree ring data as changes in ring width could also be caused by changes in aridity, it is not at all clear that proxies strongly reliant on tree rings have adequately differentiated the two signals (temperature and aridity) these two variables could act together in complex ways and make the individual signals quite vague. It may even be worse at some sites where solar radiation is limiting. Never the less, the data from the last few hundred years or so indicates a rapid change of considerable magnitude which we all need to be concerned about.
I'd be interested in some opinions on this - RC reckon everyone except Van Storch has missed the point .. ..
"So what would have happened to the MBH results if Wegman and his colleagues had been consulted on PC centering conventions at the time? Absolutely nothing. "
Wrong stats but right answer??
http://www.realclimate.org/index.php/archives/2006/07/the-missing-piece-at-the-wegman-hearing/#more-328
David Elder - "In future I will simply give you enough rope and let you hang yourself"
Sure mate. If this makes you feel better then go for it. Perhaps while you are waiting for me to swing you can educate yourself so your posts can in future contain some information rather than climate audit bullshit.
Ender: we'll have to stop meeting like this. It's bad for both our blood pressures. In future I will simply give you enough rope and let you hang yourself.
Walter - "MWP in the western U.S, more pronounced episodes of aridity during the mid-Holocene, major climate shifts not attributable to CO2. Worse yet, in Science and peer reviewed. This is heresy. Where is the Inquisition now that it's really needed?"
Walter why is this heresy? We all recognise that climate shifts have happened in the past before humans. That does not change in any way our responsibility for this one.
Also it illustrates the winners and losers. If the MWP was indeed a global event it caused a period of plenty for Northern Europe. However the losers are very well illustrated by this study. This sort of deflates the warm is good argument. In any climate change event, other than an all out ice age, there are winners and losers. In the MWP Northern Europe were probably the winners and recorded the event however, it is not recorded who the losers were because they died out and did not leave records. In short history is written by the winners.
This climate event will also have winners and losers. The problem is who will be the losers and what will they do while they are losing. Also you or I do not know, and no-one can predict the ratio of winners to losers.
Jeepers - nobody is saying that CO2 is the only driver of climate. So why is this heresy? If you think that - it simply shows how misrepresented the AGW case is in your mind. There have been a number of paleo climate modelling studies. Welcome to the real world Walter.
So imagine the USA enjoying this climate today?? I'm sure they'd flick a techno fix and emerge totally unscathed (not!).
So what would a good helping of CO2 do on top of your Holocene shift??
Incidentally do we have an indication of what drove the alleged global MWP.