Bishop Hill Rob W in the Courier
Jul 20, 2012 Climate: MWP While I was away, there was a bit of a kerfuffle over the new paper by Esper et al. The authors claimed that Northern European temperatures were warmer than today in both the Medieval and Roman Warm Periods. Anthony reported the story at the time.
The kerfuffle came over subsequent newspaper claims that the paper disproved the AGW hypothesis (I haven't seen these claims myself, but no doubt they are out there). Readers may therefore be interested to see the response of Rob Wilson, one of the co-authors of the paper and an occasional commenter here, in his local newspaper, the Dundee Courier.
Some climate change sceptics have leapt on this as proof global warming does not exist, but Mr Wilson said no such conclusion could be drawn from a study which concentrated on one geographic area.
He said it has become ''expected'' people on both sides of the climate change argument will seize on certain parts of research to back up their own arguments, ignoring other data does not support their conclusions.
''It can come from both sides and I think there will be a few climatologists on the other side who will find issue with some of our findings,'' he said.
However, he made it clear the study does not disprove rising temperatures since the start of the 20th century are down to the actions of humankind.
I make a similar point myself in the Hockey Stick Illusion. Current temperatures can be entirely precedented and the AGW hypothesis could still be true. Equally, temperatures can be unprecedented and the hypothesis could be false.
That said, if temperatures do turn out to be nothing out of the ordinary (and I don't think we know either way yet), then it does rather reduce the cause for immediate alarm.
Reader Comments (27)
Come to think, AGW rests on no falsifiable assumption so in theory, the AGW hypothesis could be false and yet the AGW hypothesis could still be true
@omnologos - we're already at the God of the gaps stage with CAGW and its mysterious "heat in the pipeline" post-hoc epicycle explanation for no warming now but lots more to come in the future.
What we can say is that nobody understands what normal is. There might be so many interacting cycles of this that and the other going on that climate never does the same thing twice. Nobody can model natural variability successfully. And those who say they have such a model which can be used to act as a control against actual conditions, well,,
Precisely. Furthermore, if we've been here before, doesn't it suggest that concerns about "tipping points" and positive feedback loops are misplaced?
omnologos
brilliant!!
btw, for the logic of arguments about AGW or CAGW, the "current temps unprecedented" matters much more to many of the believers than to the critics. Of course there is so much much more to assess than some simplistic global comparison of late 20th C temps to 10th-13th century (or whenever) temps.
As a recent example of a simplistic attempt to make an "unprecedented" claim seem important for one region (which was not even accurate according to their own study) as the basis for hyping up AGW, one need look no further than the press event on May 17, 2012 held by David Karoly and Joelle Gergis (I posted about this with link on the Gergis thread).
So, yes, let's not allow exaggerations in EITHER direction (or multiple directions) about the significance of one region or one study etc., or one biased type of proxy in the Mann "hockey stick" work, etc.
But this science is post normal. You can lie and cheat as much as you like because 'the cause' is good.
Tree rings are not thermometers regardless whether the result supports or disproves CAGW.
However, he made it clear the study does not disprove rising temperatures since the start of the 20th century are down to the actions of humankind.
But of course. But one does not need to disprove that which is not proven.
There is no need to 'disprove claims global warming is man-made.' It is incumbent upon those who make the claim to prove beyond reasonable doubt that it exists, and is man-made.
The Esper et al paper actually contains an interesting implied conclusion about the climate sensitivity in the Northern Scandanavian region. On pp 2-3 the authors state that the June-August orbital forcing (cooling) in the region over the past 2000 years is -6 W/m^2 and that this has given rise to about 0.6 deg C of summer cooling over the same period. This works out to a sensitivity of 0.1 deg C per watt/m^2. Taking the accepted value of 3.7 watt/m^2 forcing for doubling of CO2, this sensitivity is equivalent to a low value of about 0.4 deg C for doubling of CO2.
It does make life difficult for climate models since they have problems raising temperatures without using CO2 as a thermostat.
It is also possible to detect an overall falling late Holocene temperature trend in the Antarctic, looking at the general Dome C temperature interpretation-
http://c3headlines.typepad.com/.a/6a010536b58035970c0134849d3d3f970c-pi
Of course, the elephant in the room is nothing to do with trivial excursions of temperature, up or down, of a degree or so within the current Holocene interglacial, but the 4 to 10 deg C drop that is humanity's fate when this interglacial terminates. I still find it incredible that each and every researcher calling him/her/self a climate scientist, does not place first and foremost their fundamental research on getting a better handle on precisely when, why and how rapidly the Icy sword of Damocles will fall.
I would be eternally grateful if one of the great brains of the Bishop Hill gang would explain to me why the ice core records are not already proof that CAGW can not be caused by CO2. If temperature can fall for 2000 years while CO2 is rising, what else is needed?
My Dear Dung: modern warming is because anthropogenic CO2 behaves differently to normal CO2.
I thought everyone knew that!
Jul 20, 2012 at 8:12 PM | Dung
There is obviousy a very complex relationship between man made CO2 and temperature: one which only 'climate scientists' can fully understand...
I'm with David.Jul 20, 2012 at 7:16 PM .
It does not disprove aliens are visiting our planet in UFO's either.
@DavidCH "There is no need to 'disprove claims global warming is man-made.' It is incumbent upon those who make the claim to prove beyond reasonable doubt that it exists, and is man-made."
Punitive taxes and legislation suggest otherwise.
Dear All,
Quick clarification to the Esper et al study:
It is the most replicated (> 500 series) tree-ring maximum density (MXD) series developed to date. It explains ~60% of the summer temperature variance for Northern Scandinavia. Agreed – this is not a thermometer reading of past temperatures, but it isn’t bad for a proxy of past climate. You will not find many records better than this.
Making any inferences about global trends from this regional record is wrong. However, it will of course become an important record in the ever expanding data-base of temperature proxy records in the Northern Hemisphere. Spatial reconstructions are the ideal, but we need lots of data (many locations) for that approach to work.
The location of the Esper et al. record (high latitude) and the fact that it represents the summer season should theoretically mean that we could/should see the orbitally forced changes of summer temperature related to insolation changes. This hypothesis is backed up with the longer term decreasing trend (-0.31oC/1000 years) observed in the MXD data (agrees with independent proxy data for Arctic by Kaufman et al. 2009). There are three warm periods that poke their heads above this long term trend – the Roman, Medieval and Current period.
The MOST IMPORTANT implication from this study, in my mind, is that the long term trend in the MXD data is NOT observed in the ring-width (RW) data. Why this is so, is the focus of ongoing work.
If there is some sort of bias in the RW data w.r.t. longer term millennial scale variability, then this has large implications for the use of other high latitude RW series (e.g. from Alaska to Labrador and Scandinavia to Kamtchatka. As previous tree-ring based northern hemisphere reconstructions using solely tree-ring data (Esper et al. 2002; D’Arrigo et al. 2006) used almost entirely RW data, then we (Esper et al. 2012) have hypothesised that it is POSSIBLE that these large scale composites may underestimate medieval temperatures. It is difficult to test this hypothesis without measuring MXD from those high latitude locations where currently almost only RW has been measured.
Mike Mann has criticised this hypothesis on RealClimate and elsewhere by quoting trends from other multi-proxy studies which is not helpful/relevant as they are derived from a mishmash of high and lower latitude proxies of varying seasons (summer and annual etc) which does not address the real issue at all.
But that's not the point Rob, Manns defence isn't designed to give anyone the truth but merely to protect their position from such horrid personal attacks like your paper.
Regards
Mailman
Looking back through geological history makes you realize that 'normal' in relation to temperature and climate means nothing but an acceptance that climates change continually and temperatures swing from cold to extra warm. This is the 'normal' we all have to accept. The fact that today we are experiencing a fairly benign climate means that we are either on the up or down slope of climate cycling.
OK I think I am with the program now:
During the last 200 years aliens have been constantly visiting our planet and abducting innocent CO2 molecules. The aliens performed obscene experiments on them, brainwashed them and then returned them to Earth. These CO2 molecules, although outwardly indistinguishable from normal molecules, are now carrying out an alien plot to fry the planet.
It is also thought that the aliens, being unable to distinguish between various biochemical molecular groupings, accidentally included some politicians in their project.
"Normal" is all about anomalies and usually anomalies are compared to 1961-90 as "normal", one of the coldest periods of the 20th C. Pretty near guaranteed to get a positive anomaly, hence "warming".
CET 1931-1960 30 year average was 9.6 deg C, 1961-90 was 9.47. Summer 1931-60 was 15.61, 1961-90 was 15.32. There was a phase shift in CET from 1986 at 8.74, to 1990 at 10.63, 1.89 C rise in 4 years. It has more or less plateaued since then, with the highest in 2006 at 10.83, since when it has declined, with a burp in 2011 to 10.71, after the cold year 2010 at 8.83.
The years 1733, 1834, and 1921, at 10.47 degrees C, were 1 degree above 1961-90 average;1959 at 10.48 degrees, was comparable to 2004. Rather than more extreme weather the trend has been for a smaller range and a move away from the extreme cold weather of the late 17th, late 18th, late 19th and early 20th century. 2006 had the "warmest ever" CET September, but that was only 0.2 deg C warmer than September 1729. The warmest CET winter is still 1869, warmest Spring 1893, Summer, 1976 and warmest Autumn of course, was 2006, thanks to the record September that year.
A press release in 1698, had the Met Office been around then, could have said “eight of the coldest years have occurred in the last 15 years”, thereby proving "global cooling" at that time.
In an e-mail to Phil Jones and others in 2005, David Parker of the Hadley Centre explained the preference for the period 1961-90:
“There is a preference in the atmospheric observations chapter of IPCC AR4 to stay with the 1961-1990 normals. This is partly because a change of normals confuses users, e.g. anomalies will seem less positive than before if we change to newer normals, so the impression of global warming will be muted."
In a 2005 e-mail, #0222, subject: RE: Fwd: Monthly CLIMATbulletins, to: Parker, David (Met Office) Neil Plummer (bom, au), Phil Jones said :
"Just to reiterate David's points, I'm hoping that IPCC will stick with 1961-90. The issue of confusing users/media with new anomalies from a different base period is the key one in my mind. Arguments about the 1990s being better observed than the 1960s don't hold too much water with me.
There is some discussion of going to 1981-2000 to help the modelling chapters. If we do this it will be a bit of a bodge as it will be hard to do things properly for the surface temp and precip as we'd lose loads of stations with long records that would then have incomplete normals. If we do we will likely achieve it by re-zeroing series and maps in an ad hoc way. There won't be any move by IPCC to go for 1971-2000, as it won't help with satellite series or the models.
1981-2000 helps with MSU series and the much better Reanalyses and also globally-complete SST. 20 years (1981-2000) isn't 30 years, but the rationale for 30 years isn't that compelling. The original argument was for 35 years around 1900 because Bruckner found 35 cycles in some west Russian lakes (hence periods like 1881-1915). This went to 30 as it easier to compute.
Personally I don't want to change the base period till after I retire!"
Note the confirmation of loss of stations. I do love it when "the science" is so settled.
Rob Wilson
Very helpful comments, much appreciated. It's kind of sleepy Saturday around here it seems, but I hope there will be discussion of what you've said. This is helpful to know:
Jul 21, 2012 at 5:38 PM | DennisA
What does this 'helps with' mean?
From the Ecclesiastical Uncle, an old retired bureaucrat in a field only remotely related to climate with minimal qualifications and only half a mind.
omnologos
Your opening contribution provoked me to investigations that lowered the ante to mere interest. I explain: (Side note to dung: this is an attempt at an intellectual exercise and will contain no knowing falsehoods. Mistakes I cannot rule out.)
Popper is well known for his assertion that the method by which science proceeds is that a scientific theory remains potentially valid until it is falsified. I now read (Wikipedia!(?)) that he went on to assert that if a theory cannot be falsified it is not a scientific theory. If therefore you are right and AGW (mankind causes global warming) cannot be falsified, it is not a scientific theory.
Maybe we all knew that anyway.
However, are you right? Firstly polarize the situation so we can ignore the possibility that mankind is partly responsible. Then examine the reverse proposition: that mankind is not responsible for global warming. Is it not theoretically conceivable that other causes could be shown to be wholly responsible? Would this mean that the proposition that mankind is responsible is falsified? Is this valid or have I merely ignored the proposition at issue and considered another one?
Just a thought.
I found the exchanges between Rob Wilson and Real Climate gurus intriguing, since evidently the Esper et al (2012) raises the bar for long term reconstructions utilizing tree ring studies (need MXD and not RW proxies as have been widely used in the past).... is it just me or does Mike Mann sound nervous and defensive (his comments at link):
RC exchange on Rob Wilson's comments re Esper et al (2012)
[my emphasis below]
Re: Jul 22, 2012 at 5:02 AM | Skiphil
Thanks for the link, fascinating stuff, and yes that would be my reading too, particularly when he wheels out 'the heavies' to respond to question two. (He has a habit of doing this when he needs back-up!)
And love his last sentence in his comment 1 response ie
"...You can expect some discussion of this in the peer-reviewed literature too. In any case, thanks for dropping by! -mike"
Wasn't that rather an invitation to leave?
And again reiterated in his response to Rob's last remarks ie
RW
"So – let’s not get too hung up on misinterpreting what our paper says. This is a regional study which shows a decreasing trend for almost 2000 years. The Roman, Medieval and present periods are above this long term trend – these trends are not relevant for southern Europe and are certainly not relevant for the globe as a whole. This record should not be used to debunk global warming and people should not get their knickers in a twist if the medieval is warmer than present in this regional record. This is exactly what would be expected from orbital forcing of summer temperatures at this latitude.
MM
"That would all be fine and well if Esper's press release hadn't extrapolated wildly from that narrow specific conclusion to calling into question the IPCC consensus about large-scale temperature reconstructions....Thanks again for stopping by in any case! -mike"
And Michael Mann is a fine one to talk about press releases - What a Hypocrite!!
http://climateaudit.org/2010/08/01/the-no-dendro-illusion/