The very first sentence of the Marcott et al (which is getting heavy press) abstract says:
Surface temperature reconstructions of the past 1500 years suggest that recent warming is unprecedented in that time.
Okay, let’s have a look at the claim. First this graph from the publication:
![marcott-A-1000[1]](http://wattsupwiththat.files.wordpress.com/2013/03/marcott-a-10001.jpg?quality=83)
Seems reasonable when you look at that data, right? But let us examine a well known reconstruction from GISP2 ice core data in Greenland. Here’s a section from Dr. Richard Alley’s reconstruction:
Now here is a simple scaling of the Marcott et al graph to get an approximate match for the temperature and time scales:
Note that this is just a simple visual comparison, with a rough match of the data for time and temperature scales – it isn’t intended to be anything else.
The full un-cropped Alley GISP2 plot can be seen below:
In my overlay above, the Marcott et al graph full time scale on the x axis is 2000 years, and its temperature full scale on the y axis is two degrees C. The scaled overlay to the Alley GISP2 plot is a reasonably close match to the GISP2 plot scale units. The centerlines don’t match, but they can’t with this sort of comparison.
The idea here is simply to compare magnitudes of the data on the same time scale.
Clearly, the GISP2 data has greater magnitudes in the past 1500 years, and at longer time scales, the GISP2 temperature reconstruction dwarfs the magnitude of the Marcott et al temperature reconstruction. Dr. Don Easterbrook has a good synopsis of GISP 2 temperature reconstruction magnitude on WUWT here.
This simple visual comparison suggests that their “unprecedented” claim for the 1500 years BP is unlikely to hold up when examined against other reconstructions. As they say in the big leagues, more study is needed.
Marcott et al alludes to the warmer temperatures of the past in this paragraph:
Our results indicate that global mean temperature for the decade 2000–2009 (34) has not yet exceeded the warmest temperatures of the early Holocene (5000 to 10,000 yr B.P.). These temperatures are, however, warmer than 82% of the Holocene distribution as represented by the Standard5×5 stack, or 72% after making plausible corrections for inherent smoothing of the high frequencies in the stack (6) (Fig. 3). In contrast, the decadal mean global temperature of the early 20th century (1900–1909) was cooler than >95% of the Holocene distribution under both the Standard5×5 and high-frequency corrected scenarios.
Perhaps this weekend when I have more time, either I can do a proper plot of the data in a similar fashion to see how well they match when plotted side-by-side in the 1500 year time frame. Unfortunately I have other work to do today, so I can’t at the moment, and I’m traveling again tomorrow. Posting will be light.
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Good point, but the Marcott analysis seems to splice instrumental records which have the highest resolution of all to those “smooth” proxies.
Bingo: “unprecedented” warming.
The worse their proxies the more “unprecedented” it gets. We’ve seen this before.
This is a replay of the Mannian Hokey Stick.
First claim unprecedented warming for 2000 years.
Second claim unprecedented in 800 yrs
Third, unprecedented in 400yrs
Fourth unprecedented in 40 yrs
Fifth unprecedented since yesterday.
Next nothing to see here, move along, but we were right anyway.
So which of these collaborators will republish, 20 years later, saying I found a accidental bias in my calculations, Oh look history is restored?
Al la Briffa, actually I am not sure how many years it took Briffa to “correct” his work.
I just found this interestin post on RealClimate. It may get removed so here are the details…
Harrison is at Reading University in the UK.
“Empirical evidence for a nonlinear effect of galactic cosmic rays on clouds
Abstract
Galactic cosmic ray (GCR) changes have been suggested to affect weather and climate, and new evidence is presented here directly linking GCRs with clouds. Clouds increase the diffuse solar radiation, measured continuously at UK surface meteorological sites since 1947. The ratio of diffuse to total solar radiation ‘the diffuse fraction (DF)’ is used to infer cloud, and is compared with the daily mean neutron count rate measured at Climax, Colorado from 1951-2000, which provides a globally representative indicator of cosmic rays. Across the UK, on days of high cosmic ray flux (above 3600-102neutron counts 1, which occur 87% of the time on average) compared with low cosmic ray flux, (i) the chance of an overcast day increases by (19±4) %, and (ii) the diffuse fraction increases by (2±0.3) %. During sudden transient reductions in cosmic rays (e.g. Forbush events), simultaneous decreases occur in the diffuse fraction. The diffuse radiation changes are, therefore, unambiguously due to cosmic rays. Although the statistically significant nonlinear cosmic ray effect is small, it will have a considerably larger aggregate effect on longer timescale (e.g. centennial) climate variations when day-to-day variability averages out.”
http://www.met.rdg.ac.uk/cag/publications/2006/harrison2006.pdf
@Mosh
Hang on Steve, the Gisp2 total temp variation is of the order of 3 degrees C, yes? Whereas, the Marcott reconstruction is showing a total variation of less than 1 deg C. Now, that is some helluva smoothing, wouldn’t you say? Irrespective of the global vs local issues, which I accept – it does not really follow to have such high temps locally for many centuries (as per Gisp2) and not have them ‘reflected’ globally.
The suspicion is certainly that the Marcott graph ‘stopped’ at 1500 years ago intentionally too!
I think someone mentioned that this is a Greenland temp scale compared to a global scale… so to be fair, can we get a copy of the Marcott et al. Greenland data to compare the two to see how they look together?
I would like to know if the Marcott source data shows that same smooth line just for Greenland, or if they are using an average to remove the Greenland spikes…
Not apples and oranges but apples and turnips.
It is a bit off topic, for which apologies, but an aspect of the original release that jumped out at me was the “it should be getting cooler” comment based, as far as I could see, on a perturbation in Earth’s orbit that means the Northern hemisphere is getting less sunlight.
I suspect that as AGW sceptics, some of you ladies and gentlemen are going to be among the world’s leading experts on the sun’s influence on climate so I was wondering whether or not you would concur with that specific element of the Marcott analysis?
So, contrary to his publicity package, it is not the case that Marcott has proven that current temps are unprecedented in the last 11k years. Rather, Marcott has shown only that IF present temps continue for another hundred years THAT event would be unprecedented in past 11k years.
If this study is using 100 year smoothing, how does that affect their near time data? Do they get their “Present” temperatures by smoothing with climate model projections or did they just stop smoothing an use thermometer readings directly? Or did they manipulate the neat term data some other way?
@Nullius in Verba, Henry Clark
The same trick of blurring many different proxies together was used in a paper posted last year focusing on the start of the Holocene (sorry no link, posting from my cell phone) which tried to blur out the Younger Dryas with the aim being to obscure and conceal the lag in the CO2 rise after the temperature rise, which is clearly resolved in individual high resolution proxies such as ice cores.
@Steve Mosher
How does your argument about CO2 sensitivity square with the observation over the last 7000 odd years since the Holocene optimum, that while temperature has declined, CO2 has steadily risen?
Also you are contradicting your own resolution “apples and oranges” argument by accepting in Marcott et al the brazen Mann-like splicing of the modern high resolution temperature instrumental record onto the low resolution proxy blur.
Looks like hiding the decline “Nature trick” to me. “What decline?” Exactly.
@William Howard McClenney
Is anyone in the CAGW movement actually aware that excursions of higher temperature occur typically at the end of interglacials?
Steven Mosher says above, “Oh and here is another thing to ponder: Imagine the Holocene was warmer than they suggest. That would imply a more sensitive climate since the change in forcing between Holocene and LIA isnt particularly big.”
If I understand correctly, this claim depends on understanding the the physics of all possible forcings, which would be very helpful if you actually do and could explain for us.
FerdiEgb has already provided a couple of citations. I am sure SM grasps the difference between a TOA radiative forcing abstraction and the physical response of the climate system to an actual physical stimulus.
We have to get rid of the Medieval Warm Period [IPCC – Jay Overpeck]
Sorry, I just can’t help focusing on exactly what some people say. Maybe it’s just a slip.
Now for some Arctic specific warm horrors. Disclaimer: in no way does this imply that the rest of the world was in any way involved.
How come the objections in this thread, and in the previous two On-Topic threads, didn’t occur to the peer reviewers?
(Rhetorical question.)
MacCracken is cracking up the rhetorics on Yahoo and the Younger Dryas… “Question is over how extensive a domain the change was felt and were there compensating adjustments—so was it mainly a realignment of the weather, and the global scale response was slower. Mike”
“Mainly a realignement of the weather, and the global scale response was slower”. This comment shows the disconnect between computer climatology and the observation based science: how do you think climatic shifts are expressed Mr. Director of the Climate Institute?
Climatic shifts are reflected through the weather. So weather “realignment” that is variation of intensity in atmospheric circulation lower layers is at least hemispheric if not global.
Peter says: March 8, 2013 at 3:16 pm
It is a bit off topic, for which apologies, but an aspect of the original release that jumped out at me was the “it should be getting cooler”
Peter … perhaps … but the Milankovitch cycles unfortunately don’t quite explain it all … perhaps a reason Arrhenius went looking for other forcings in the first place….
Problems
http://en.wikipedia.org/wiki/Milankovitch_cycles
Tim asks to see Marcott’s Greenland data.
The only Greenland data listed seems to be the Agassiz-Renland ice core series from Vinther et al., “Holocene thinning of the Greenland ice sheet” Nature, 461, 385-388, 2009, doi:10.1038/nature08355
Pic here:
http://oi49.tinypic.com/15zo40h.jpg
As I said above, there’s a bunch of high-temp records with peaks around 1-3 C mixed in with a whole bunch of basically flat ‘random noise’ records. The flat records dilute the size of the peak without changing its shape – the argument is presumably that the Holocene Optimum only occurred in some places, and therefore the global average is much lower than local averages.
Mann’s treering data looked similar – there were a few lumpy records and a lot of series that looked like flat random noise. In that case, they emphasised the lumpy records because they had big spikes upwards at the end, but the suspicion was that none of them were measuring temperature and the lumpy ones were simply corrupted.
Whether you choose to believe that some parts of the world rose in temperature up to 3 C while others saw no change at all, or that some of the proxies are not very good thermometers is up to you. But there’s no big surprise that if you average data with a bunch of flat series then the result will flatten out. And if you sample at long intervals then any blips happening on timescales of less than a thousand years will simply not show up.
The sin is splicing in the modern temperature record, and claiming that a 30-year spike is shown to be ‘unprecedented’ by comparing it with a reconstruction in which spikes shorter than 3000 years are attenuated, and those shorter than 300 years eliminated entirely.
Please keep in mind that us ignorant amateurs are trying to learn from WUWT and things on the charts that are obvious to you need a little explanation. For example. -31.00 C?? Dang! It was cold during the Roman Warming period.
Funny they didn’t use the famous GISP2 temperature proxy. Famous that is.
You know what, only 1 of the proxies used (out of 73 of them) show anything like the 0.6C spike at the end of the chart (which is 1940).
Theonly proxy which has this is Agassiz-Renland ice cores (dO18 calibrated to borehole thermometry again).
So, this reminds me of the 1 tree in Briffa’s reconstruction.
Here is Agassiz Renland against the main temperature stack from the paper (which appears to be the only proxy which made the 0.6C at the end ).
http://s2.postimage.org/j4zwjyxmh/Marcott2013_Ag_Ren_ice_core.png
(see if you can find another one which would contribute to the end spike – Excel file of the data)
http://www.sciencemag.org/content/suppl/2013/03/07/339.6124.1198.DC1/Marcott.SM.database.S1.xlsx
Agassiz-Renland temperature reconstruction which appears to be the same as in the data file.
http://www.iceandclimate.nbi.ku.dk/data/Temperature_Reconstruction.pdf/
I’ve posted this before, but no-one seems to see the importance of it, and it seem relevant here:
The main researcher telling us there was no Medieval Warm Period is Mann, and his publications are oft cited on the matter. He published world maps showing colour coded temperatures compared with the recent 1960 to 1990 reference mean and most of his MWP world comes up blue (colder)…
But he has based it on a couple of dozen variously weighted proxies, most of which show warming.
Here are my thoughts on it again, for what they are worth:
It is really worth going back to assess Mann’s original contention that the MWP was ‘cooler than the present’ (of course, he has to rename it the MCA, the Medieval Climate Anomoly, as otherwise the whole thing would fail the Orwellian test).
Available here: (needs a log in – no cost) Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly. Michael E. Mann, Zhihua Zhang, Scott Rutherford, Raymond S. Bradley, Malcolm K. Hughes, Drew Shindell, Caspar Ammann, Greg Faluvegi, Fenbiao Ni
http://www.sciencemag.org/content/326/5957/1256.short
http://www.sciencemag.org/content/326/5957/1256.full.pdf
Note Figure 2 – the top figures showing the temperature anomaly map of the world for the MCA (compared to the 1961 to 1990 period) ..and the weighted proxies on the right…to me it is an incredible construct: Note all the blue (cooler than recent times) on the map.
However, most of the proxies used show warming in their immediate area!!
Starting in northern America we see a cluster of proxies – by the temperature anomaly map, all apparently warmer than now, except for one cooler site. Down to the Caribbean … neutral, but heavily weighted.
Peru, Ecuador, looks like it was warm there…. back up to Greenland … a very warm spot…, across to Europe, only two proxies, one heavily weighted, but both warmer, across to northern Russia …one isolated proxy with an isolated warmer spot … to central China, there is a cooler spot …then head a bit east in China..another very hot spot…then all the way down to Tasmania and New Zealand – Tasmania is cooler, NZ is warmer than now…… Back to Africa, 3 proxies, one cooler (and heavily weighted) and one very lightly weighted and warmer, and one neutral…
Then look at all the modeled cooling on the map … right across central Asia, based on 4 proxies (!!), all of which were warmer except one…
ALL of the Southern Ocean, the southern Indian Ocean, and southern Atlantic oceans were supposedly much cooler, (based on Tasmania, and three proxies in Africa?!!) All of the eastern Pacific is shown as cooler, … based on a string of proxies in the western Americas, which were mainly warmer, and perhaps eastern China ..which was warmer anyway?
See Fig. 2. It shows reconstructed surface temperature pattern for MCA (950 to 1250 C.E.) and LIA (1400 to 1700 C.E.). Shown are the mean surface temperature anomaly and associated relative weightings of various proxy records used (indicated by size of symbols) for the low-frequency component of the reconstruction. Anomalies are defined relative to the 1961– 1990 reference period mean.
Now I do appreciate the vast effort and detailed measurements and complicated science which have gone into this effort, but thinking it is related to reality to me it is rather like building an intricate model of a Boeing 747 with Lego blocks (a truly mighty effort indeed) and then selling flight tickets to London.
Steven Mosher says “Oh and here is another thing to ponder: Imagine the Holocene was warmer than they suggest. That would imply a more sensitive climate since the change in forcing between Holocene and LIA isnt particularly big.”
Here’s something for Steven to ponder: If the polar jet switches from a fast polar flow to a weaker meridional flow, what is the effect at TOA? Typical modeler answer is that the polar jet is a feedback just like all other weather so can’t affect the TOA flux. Typical modelers in the early 2000’s said the Arctic polar jet would get stronger especially in winter due to the decrease in sea ice because of the increased longitudinal temperature contrasts. Sure enough the polar jet had generally strengthened through the 1990’s to match the models.
A typical modeler nowadays would say that the Arctic polar jet will become more meridional due to lower latitudinal temperature contrasts and that would make the jet weaker. Sure enough the polar jet got weaker through the 2000’s to match the models.
One thing to ponder is that the changes in the real world weather preceded the changes in the models. Another thing is that solar activity decreased through the 2000’s. The forcing didn’t change a lot like you say, but that’s only considering TSI which is does not affect weather very much. What is much more important is that the solar spectrum changed which caused weather changes such as lower UV connected to more blocking (e.g. Lockwood 2010).
So what you consider sensitivity of the climate may actually be long term changes in weather due to long term changes in solar activity. The next decade of changes will likely clarify the issue and there is obviously no need to do anything while the global temperature rise is so small.
Is there a complimentary (not behind paywall) online version of the Marcott et al 2013 paper?
Annoying not having ready access.
John
They do it for the headline. They don’t care if it is proven to be rubbish afterwards. They’ll ignore that part and assume the general public have moved on – no doubt to look at their next “shocking” headline.
Funding has got to be pulled on the enviro-whackos, right across the board. It’s the only way short of violence to stop these people. What they are doing is criminal. More than that, it’s treason. I’m surprised more people don’t see that their aim is the total destruction of everything that has gotten humankind out of caves and into civilization. And we’re PAYING them for this destruction??? I say, pull the plug.
Post (see below) on BH with link to standardized plot of all 73 proxies without statistical alchemy. This graphic, plus the geographical distribution of the 73 proxies (nearly all are coastal/marine locations, with large regions of both land and sea not represented), makes one want an especially thorough audit of the study methods that yield claims of such a distinctive hockey stick pattern as globally significant.
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rogerknights says: March 8, 2013 at 4:16 pm “How come the objections in this thread, and in the previous two On-Topic threads, didn’t occur to the peer reviewers?”
I doubt that comparing a global temperature reconstruction with part of a (flawed) drawing of temperatures high on an arctic ice sheet would have occurred to anyone else, not just the peer reviewers.
I always go back to the raw data to see how much massaging might be needed to arrive at the final synthesized plot. After looking closely at all data and plotting each of the 73 proxies, I make these observations:
The “blade” of the hockey stick is made up of a single point centered at the year 1940 (1930-1950 bin). The next point is at 1920 (1910-1930 bin) and is actually an anomaly of less the zero. The slope between these last two points is 0.35°C/decade.
None of the proxies remotely resembles the final synthesized plot shown in the Marcott paper. Most have temperature ranges much larger than the final chart. 24 of the 73 proxies contain data after 1910. Only 9 proxies have more than one data point in this region, permitting a slope determination. Of these, 5 end with a negative slope (decreasing temperature), 3 have a positive slope (increasing temperature) and 1 has a zero slope. The 9 proxies contain only 33 measurements beyond 1910. The average 1910-1950 slope for the 9 proxies is 0.13°C/decade, about 1/3 the value shown in Marcott’s overall plot – and barely enough to bring the final data point back to a zero anomaly – a much less dramatic plot. Hmmm….
None of this invalidates Marcott’s conclusions. I’m not a statistician and my analysis was quite simple. I have not looked at the spatial distribution of the data. However, I think a thorough examination of the statistical methods used by Marcott might be warranted.