I’ve never been much interested in the detail of the famous ‘Hockey stick’ debate. This graph summarises what Mann et al put forward:
Mann’s original article was about uncertainties in Northern Hemisphere temperatures. I noted the instrumental record part towards the end and how this corresponded to the massive burning of fossil fuels. I concluded that the shape of the stick part doesn’t matter much.
Now a new study has brought the matter to life, for me at least.
But to understand the new information appropriately it is probably necessary to sketch in the context of the debate.
One of the memes pushed by AGW opponents is that the Hockey stick is a proven myth if not a fraud. The New Scientist has a very accessible summary which concludes that it is not a myth.
In fact, later studies support the key conclusion: the world is warmer now than it has been for at least 1000 years
An article by Rich Deem gives us this 2005 graph by Mobious et el:
Deem concludes:
although the absolute magnitude of climate variation is still in question, all data show a rapid increase in global temperatures during the 20th century that has not seen in the preceding 2,000 years.
A more frontal attack comes from this pair of graphs which is sourced from the UK Telegraph via the Citizens Electoral Council:
The source of this graph appears to be one Richard S Lindzen.
So we are in the territory of Lindzen, the Lavoisier Group and Professor Bob Carter, which is not where interested laypersons such as I go for reliable climate science.
The purpose of that graph is to minimise the impact of recent warming and to make it into background noise indisdinguishable within the natural fluctuations.
It has gained no traction within the mainstream of peer-reviewed science. Quite the contrary.
Some of you will know masses more about this topic than I do. Others may want to increase their knowledge by reading a fairly detailed entry in Wikipedia, Michael Mann et al’s 2008 renewed attempt using more recent science, and treatments at RealClimate here and here.
The importance of the new study is twofold. First it confirms that what we are dealing with in the mediaeval warming is a regional phenomenon. Whatever the force Lindzen graph has derives from its being mistaken for a global phenomenon.
Secondly, the exploration of possible causes has interest for the future of regional climates.
Valerie Trouet at the Swiss Federal Institute for Forest, Snow, and Landscape Research in Birmensdorf looked at proxies in Morocco and Scotland. Morocco’s weather is strongly influenced by the Azores High, Scotland’s by the Icelandic Low. The pressure difference between the two which produced an extended period of warming reflects, was, she thinks, “a strongly positive North Atlantic Oscillation (NAO) – the ocean current that drives winds from the Atlantic over Europe.”
Now why would this be?
“It turns out that in the tropical Pacific, the El Niño system was in a negative La Niña mode, meaning it was colder than normal,” says Trouet.
And why would this be?
Trouet thinks external forces like abrupt changes in solar output or volcanism must have started and stopped the cycle, and hopes to pinpoint the most likely candidates in a workshop with other climatologists in May.
Now here’s the interesting part for us:
Michael Mann at Pennsylvania State University says that based on the analyses and modelling that he has done, increased solar output and a reduction in volcanoes spouting cooling ash into the atmosphere could have not only kicked off the medieval warming, but might also have maintained it directly.
Mann is also concerned that the dominance of medieval La Niña conditions now indicated by Trouet’s work might make it more likely that the current man-made warming could also put the El Niño system back into a La Niña mode, although most climate models so far had predicted the opposite.
“If this happens, then the implications are profound, because regions that are already suffering from increased droughts as a result of climate warming, like western North America, will become even drier if La Niña prevails in the future”, he says. (Emphasis added)
Bad for western North America, but good for eastern Australia, as I understand it. But not much relevance to southern Australia which is more subject to what comes from the west in the Indian Ocean.
Update: The Feral Abacus (@1) has kindly sent my a copy of the article by Trouet et al, plus supporting documentation. I can’t guarantee that I understood it all, but FWIW this is what I made of the issue TFA raises.
Trouet and team made no new measurements, they simply worked with the research available. They saw the Scottish and the Moroccan studies as
strategically sited and sensitive to atmospheric variations in the southern and northern nodes of the NAO dipole, provide us with a basis for extending the instrumental winter NAO index back to the MCA [Medieval Climate Anomaly].
The 2007 Moroccan tree ring-based drought reconstruction study (J. Esper et al) covered the period 1049-2002. The 2000 Scottish speleothem-based (stalagmite) study (C. J. Procter et al) covered 900-1993. Both were precipitation proxies.
Because both covered the instrumentation period as well as earlier periods when multiple proxies were available from multiple sites, they created and calibrated a new index to cover the earlier period.
Their methodology in how they treated data is set out in detail. I wouldn’t presume to comment on it, except to say that what they have done may or may not be confirmed by further research. I think TFA’s concern is how definitive you can be in your inferences. It’s a fair point, but I’m not qualified to comment.
This image, which you can get by googling, indicates in general terms what was going on. The triangles, dots, squares and stars indicate the locations of data from other studies they took into account. To go further you need to pay your money and read the article, the supporting documentation and the constituent studies as well.
The blue patch in the Pacific they refer to as “La Nina-like conditions”. They don’t call it La Nina as such.
The ocean circulation pattern portrayed is referred to as the “Atlantic meridional overturning circulation” (AMOC), which, I gather, is the Atlantic part of the thermohaline circulation. Let’s say they see AMOC as implicated.
Brian, the claim that medieval warming was a regional phenomenon looks more than a bit soft. From a quick read of the New Scientist article you linked to it appears that this conclusion is based from data from just two widely-separated locations. Not enough, in my book, to be saying anything definitive about the geographic extent of warming at that time.
This does support the archeologists’ & historians’ contention re Northern hemisphere warming and the questions they posed (I know I’ve posted this before, but been howled down; although the evidence was widespread and supported by documentation):
After the Little Ice Age, a return to the warmer temperatures of the Viking-Norman period was to be expected (Note that the graphs only cover the last 2000 years, omitting the previous “warm period” which encompassed Greece’s Golden Age – Hannibal’s crossing of the Alps in winter was probably the last time army could have; therefore, we do not know how hot the Viking/Norman Era relative to earlier war eras:
*The first signs that the Little Ice Age was coming to a close were the surprisingly hot summers in the early 1750s, so hot in England that men took off cravats, undid shirt fronts to mid-chest or lower, unbuttoned or discarded waistcoats, and often discarded coats as well – and are depicted thus in art and ceramic figures Note:This occurred before the real impact of industrialisation on “greenhouse gases” c1830+; (when the IR encompassed widespread use of gas, steam-powered machinery & transport and spread beyond England;
Viking Era temperature peaks (those B**ody Canadian grapes again!) have not yet been reached;
In Australia (S Hemisphere), existing temperature records indicate that the early part of the century (tho the last decade of the previous century should be included) is marked by drier, hotter temperatures; whereas the third quarter into the fourth are cooler & wetter – some heat records from the early part of C20 still stand; others were broken only in this year’s heat-waves.
The questions, therefore, are: To what extent is human intervention (inc deforestation) to blame for current global warming? and As current temperatures are still below the Viking level and likely to continue to rise for some time even if all human CO2 production is shut down immediately, what will be people’s reactions to the failure of even the most stringent measures to reduce global temperatures?
BTW: What happened to SO2 & acid rain, the BIG factors in the first round of GW hysteria in the late 1960s? (Try listening to Hair again!)
DeeCee, SO2 and acid rain were addressed quite firmly in Europe and to some extent in North America. So the answer seems to be that removing the cause of pollution problems is both effective and achievable. Perhaps we could try it with CO2 as well?
The science… I don’t know the details, it’s not my field. But from my point of view the question is: does AGW give people an acceptable reason to do what I think they should be doing anyway? If so, I’m all for the campaign. From my point of view energy efficiency measures that have short payback periods should be strongly encouraged if not mandatory, like the rest of the “stingy green” measures. Why waste stuff just because we don’t have an immediate use for it?
I concluded that the shape of the stick part doesn’t matter much.
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I think it does in terms of political communication. The hockey stick is an oversimplification designed to draw our attentions to the spike in warming. When one views the actual data, which are based on various estimates derived from different sources, there is an obvious wave motion. It’s easy to dismiss the current warming because it doesn’t look as high.
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The hockey stick amplifies matters.
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But the trouble is that it can then be easily challenged and has been by even more dishonest distortions. That last graph in this post is the worst example of scene as yet. It shows the Medieval Warm Period to be a sweltering day in comparison to our mild one.
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In The Weekend Australian Christopher Pearson ran a blatant spruik for a mate with the following hyperbole:
Plimer backs up the line advocated by those who made the aforementioned graph:
I have no way of knowing directly what the climate history of this planet actually was. But if the medieval warming was greater than the late 20th century warming that means there’s a helluva a lot of scientists and science journalists out there conspiring to snow me.
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Pilmer’s book appears not a work of science fact but a political polemic. In it he runs the familiar line that this is all a delusion born of a kind of quasi religion. He compares the situation to Lysenko’s retardation of Sov agriculture. I can’t comment on the book’s veracity in any way. But I’m quite skeptical of someone whose mission is to debunk what he thinks as a sciencistic fraud and then spend most of the time regurgitating the standard messages of News Ltd columnists.
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Funnily, Pearson, acknowledges that the Lysenko comparison is a bit much considering that there is no agent capable of globally inflicting Stalinist control on world science. Somehow however large groups of scientists have nevertheless been hoodwinked into a religious delusion that aims to derail the world’s economy.
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Except Pilmer of course.
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You know he’s objective because he says exactly the same things that Pearson and Bolt do.
TFA, I was hoping that someone better informed than I would comment, but they are all off stoushing on other threads.
I couldn’t turn up Trouet’s original paper, but I suspect that the differences between Morocco and Scotland may be as Tahiti and Darwin in relation to the SOI. In the article Trouet’s team found that:
They say also that
Both of which would mean a somewhat warmer Europe. They, and Mann, are taking this as certain and Trouet is convening a meeting of climatoligists in May to work out why.
But I don’t think anyone expects such warming to go beyond the error bars set out by Mann (not shown in the cleaned up first graph in the post).
DeeCee, have a look at the section “What happened in the past?” in The New Scientist’s section on Climate Change. They warn about anecdotal evidence and stories of grapes in Newfoundland etc.
There is also this graph. Mann’s 1999 graph is one of the warmer ones. His 2008 one (see post) is a bit cooler.
I haven’t made a special study of temperatures in the Holocene, but here is one of the few graphs I’ve found. In fact if you take a longer view there seems to be a pattern in interglacials – they peak earlier and then drift towards the new ice age.
So I’d suggest that higher temperatures in the last 8000 years don’t in any way destroy the notion that humans are warming the planet. Quite the reverse.
It’s a bit confusing. Mann’s Hockey Stick graph was held up by the IPCC and others to be the poster child of proof that humans are indeed causing harmful global warming/climate change. Now we read this:
“The importance of the new study is twofold. First it confirms that what we are dealing with in the mediaeval warming is a regional phenomenon. Whatever the force Lindzen graph has derives from its being mistaken for a global phenomenon.”
Was the Hockey Stick graph based on regional data or global data? Was the Medieval Warming Period confined to North America or is there evidence of a global warming during this period as well?
If the Hockey Stick graph was based on regional data, why was it touted (by IPCC scientists) as proof that recent global warming was caused by mankind, and why now (when under attack) is its importance being minimized by making it a regional event?
I reckon Mann is up for an Agincourt for the call on a La Nina link under global warming when both the models and climate obs are pointing the other way (He is a famous exponent of the long-bow, and is usually pretty good in his aim – not this time). I haven’t had time to look at the North Atlantic Oscillation ENSO links yet, but know there is another oscillation that affects mean rainfall in Australia that is longer than the El Nino / La Nina dominated phases that mostly influence interannual rainfall. So a wider link is plausible, but way too early to predict and probably will continue to be El Nino-dominated with warmer conditions.
A bit of history re IPCC – the first Mann et al paper came up close to the time when the Third Assessment Report was being finalised and the lead authors of the summary gave it prominence – more than I would have because of the N hemisphere bias. This is always a risk when it’s one piece of research, but analyses since have backed it up – the later review in the US backed the analysis broadly but was more conservative on how far back the conclusions on temp should be – recent warming was unprecedented for 400 years instead of 1,000. The review allowed that the data suggested warmer conditions for 1,000 years but were more conservative on their call of precedence. Michael Mann has never been shy about his conclusions – and that has got him into trouble more than once (likes a stoush!).
The hockey stick only really represented the N Hemisphere but slowly more S hemisphere data is coming in – still very uncertain. As a southern hemisphere scientist I reckon the N hemisphere as global meme is always being run. So I think all proponents have run with this meme more than they should have.
But – the footprint of the MIA and the LIA warming and cooling is very different to the later greenhouse warming – this is the most important finding made by a number of authors, more important than the average temperature is “warmer than” finding. The warming footprint conclusion is very robust but discounted by skeptics because it’s a model-obs data reconstruction and analysis. However, observation-model reanalysis (where models are used to fill the gaps in the data) are now a mainstay of climate science and is one area where investment in models is paying a handsome return in forecasting and warning and analysis of extreme events. It also allows us to distinguish human-induced environmental change to land and ocean systems that is not climate-driven.
The latest global mean temperature is warmer than any time in the past 1,000 years and shows a very different pattern to earlier fluctuations. Hockey stick = science with stoush
Roger, thanks for that excellent summary. As I’ve said it’s not an area I’ve had my head into, but I thought the Trouet research was worth giving some air and couldn’t find any other blogs that had picked it up.
DeeCee, about the Australian record, again I haven’t made a study of this topic, but one day I spent some time digging around on the BOM site in relation to Brisbane. There were indeed noticeable differences during periods of the last century in rainfall and temperature. I understand, though, that overall in Australia the temperature has gone up over the century at about the global average or a tad above. Also I hear repeatedly that the Murray-Darling dry is more significant now than earlier extended droughts because of greater evaporation of existing water, and less run-off because of the higher temperatures. You also need more rainfall to grow dry-land crops with more heat.
Brian @ 6. Pathetic! Illogically using “false accusation” (argumentum ad hominem: a logical fallacy in which one attempts to discredit information, opinions, or questions by discrediting the person who is raising the issue) is irrational and unethical. I did NOT use “anecdotal evidence” and you have provided no evidence to support your false accusation that I did.
Piecing together a past for which there are no reliable scientific measurements of climate, weather etc (as indicated in the graphs above), is the work of “hard science” scientists, social scientists, and historians. I spent decades in a position where I had to keep abreast of developments in the sciences underpinning archeology; in my case within a framework of multi-disciplinary triangulation – and changing climatic conditions and their effects on human behaviour are among the greatest problems that scientists in the field have tried to solve. Probably the best-documented recent example is a long 1990s multi-disciplinary, multi-national investigation into odd tree-ring patterns in a recovered log which led, through dendrochronology, ice-core examples, vulcanology & other sciences, history & literature (including “The Wasteland” episode in the Arthurian legends; Chinese texts and Byzantine records (see below), to discovery of the C6 AD eruption of Krakatoa & confirmation of it by underwater exploration:
Extreme weather events of 535–536
<a href=”http://www.qi.com/talk/viewtopic.php?p=149441″
Thanks to a TV documentary, at least two books (inc Key’s), many articles, this is the best known (but by no means the only) example of how archeologists & historians construct their time-lines, climatic & botanical conditions, and histories (although most stop short of Key’s leap to creating the Mediæval Era). Note also that they expect their theories to be subjected to very robust debate and rigorous examination. Certain elements of the Climate Change movement seem unwilling to tolerate such debate from those whose well-supported stances differ from their own!
If great scientists like Stephen Hawkins welcome having their theories subject to robust open contest – even, in Hawkins’ case, alter theories as a result and state so publicly – so can Climate Change protagonists. Currently climate is warming (all but “deniers” like Bolt accept that) & has been since the middle of C18; however there are multiple, equally well-supported (by rigorous research) theories on how much is human intervention, by what factors, what will happen in the future, and what (if anything) can mitigate or reverse it. Intelligent people regard such debate as healthy, and the way forward through contested fields.
Sorry, DeeCee. I read this:
and skimmed over this:
which takes it beyond the anecdotal.
My bad, and my unreserved apologies. It wasn’t intended to be ad hominem but I can see that it could have been perceived as disrespectful and off-hand.
But I’m not sure where that takes your argument. Yes, climate changed in pre-industrial times. Long-term the dimensions of those changes are impressively large. By comparison the temperature during the last 8,000 years has been reasonably constant, although as humans perceive it and conduct their business the changes were quite significant. In my experience we only operate with comfort within a range of about 8C. But when the industrial age really took off and produced substantial amounts of CO2 and other climate forcing greenhouse cases the temperature changed around 25 times faster than it did coming out of the last ice age.
I don’t know of anyone who claims that human activity is the only factor in current global warming, but I have yet to see any of these “multiple, equally well-supported (by rigorous research) theories on how much is human intervention, by what factors, what will happen in the future, and what (if anything) can mitigate or reverse it” that stand up.
I really didn’t intend this thread to retrace all the arguments about AGW. What impressed me about the article was the way large circulation systems that bring us our climate interact with each other and, according to the article, can produce significant (in human terms) regional variations that last for centuries.
I might have to do another post with some other examples to make the point.
You mustn’t get out much, Brian. Try Al Gore for starters.
GregM, I’d only accept that if Gore actually said that human activity is the only factor in current global warming. I’d be surprised if you could quote him saying just that.
One of Gore’s faults is that he sometimes omits saying things and thereby ends up giving a false impression. The most egregious example is where he shows the graph of CO2 in the atmosphere heading for the ceiling and uses that silly hydraulic lift stunt to rub it in. He should have explained to the uninitiated that the CO2 concentrations do not correspond to temperature rises in a straightforward manner. In other words he assumes that his audience knows about the concept of ‘climate sensitivity’ or, more likely assumes that they don’t know and takes advantage of that. Which is naughty, very naughty.
Hansen OTOH explains that there is a variety of forcings, some negative and some positive, and gives a bar graph to identify their values.
You mustn’t get out much, Brian. Try Al Gore for starters.
Supplying some evidence for this claim would be a great start.
One of the little ironies is that if the climate was more variable in the past it implies that the climate sensitivity is higher than expected. If the original hockey stick is a accurate representation of global climate, then that implies a relatively low climate sensitivity.
<blockquoteGregM, I’d only accept that if Gore actually said that human activity is the only factor in current global warming. I’d be surprised if you could quote him saying just that.
Brian, can you point out to me anywhere in his promotional vehicle “The Inconvenient Truth” where he pointed out anything other than human activity as being the cause of the current global warming?
Since your assertion was:
I think it is incumbent on you to point this out rather than segueing into his other misrepresentations.
This is not to say that I do not believe that human activity may be causing global warming (I’d be surprised if it were not) but I’d like to see the debate discussed at a fact-based level and not on the basis of unfounded assertions.
The Mann Hockey Stick is severely dodgy:
1) The Principal Component Analysis (PCA) performed in that study was deficient in robustness testing. The follow ups were weak, and do not justify the conclusion that it has all been “sorted”
2) if simple “pointwise” averaging of the component time series does not give the hockey stick, or warming signal of some sort (which it does not), then we are on shaky ground. If one needs to resort to PCA, then that is a much weaker result than more straight-up methods (such as point-wise averaging). As far as I can tell, the case has not been made that PCA is even the most relevant tool for the job. Even if it were, Mann’s application of it is highly non-robust to leaving out particular proxies.
3) The hockey stick has quietly been downplayed by even the IPCC. It is bunk.
These are interesting times for science and public policy. I fear the science has been thoroughly hijacked, though.
GregM, this thread isn’t about Al Gore. I’m not going to play.
I’ve done an update at the end of the post which is a response to the matter TFA raised @ 1, which is more interesting I think than hacking over old arguments that aren’t going to convince anyone to change their minds.