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.
Zctek,
Thanks for your reply. I am an Engineer, not a PhD Climate Scientist or Physicist, and wouldn’t attempt to answer your question authoritatively. I don’t agree one can judge the validity of ACC (Anthropogenic Climate Change) by looking at the political nature of the IPCC. It is of course political, as are most large bureaucracies. But that doesn’t mean it’s wrong on the Science. I am looking instead to statements issued by World premier Scientific Societies, calling the IPCC conclusions “compelling”, and the 10s of thousands of Peer Reviewed papers supporting ACC vs the couple of dozen according to an article in Science, that question ACC. To moderate my earlier comment, all I suggest is skeptics publish to establish Scientific credibility for their case. Since there are so few “anti ACC” peer -reviewed papers around, it makes one wonder about the strength of their case.
@Bill Illis- I found a couple more.
After a good kick in the pants last nite to not assume just because everyone else was saying it, I dug in.
To the extent that I could within my limited expertise, I started picking things apart. First I tried to find a description of where the data for the “blade” came from.
I learned “BP” was 1950 as many correctly commented. I manually identified by reading each data set there are only a handful of the data sets that cover the period after approx. 1900. In skimming these data sets temp records for the 1900 and onward period, where the “blade” shows up, nothing jumped out at me.
I learned Marcott’s graphs showed their “Temperature Stacks” data. While some of the details are over my head ( like how they calculated the numbers) I have a rough idea of what they were talking about.
As I looked at the “Global (°C)” data for the appx 1900 onward period the “blade” started to become clear. There are a handful of the data sets with large changes upward from appx 50 yrs BP (1900) to 10yrs BP (1940). I graphed in Excel each of the temperature stack data sets and there are a number of blades shown.
So the blade is clearly there the last 50-70 years or so before 1950 using the authors temperature stack data. How they computed that data is over my head. One of the stats guys will need to look at that.
I wasn’t ready to give up so I went back thru the records that included data for the 1900 and later period. There were roughly 25 data sets that covered some time period after 1900 or so.
About 8 jumped right from 1950 back 200 or more years for their next measurement – it appeared to me these offered essentially no relevant “blade” data – as you can’t calculate the increase for the 1900 onward period, even though they report a 1950 or so data point.
7 more had decreasing temps during the time period – although generally relatively small. 6 had smaller temp increases – from 0.08 to 0.31C during the time period. One – Vostok Ice – has no data for the first 6 periods going back to 150 years BP and thus no useful information re: the blade..
The remaining 3 data sets did see large warming swings during the “blade” period – these include:
MD98-2181 – Published age 1947 (BP-2.60), had a 1.16 C warming 1897 to 1947
Agassiz & Renland Ice Core – Published age 1960 (BP-10), had 1.58 C warming 1880 to 1940
TN057-17TC – Published age 1950 (BP 0), had a 2.14 C “mean” warming 1904 to 1950
These are the only 3 data records out of 73 with a large “blade” during the 1900 and later period.
Plotting the Temperature Stack data for the different columns shows a blade pattern for appx 1900 and later in the following sets:
“Standard5x5Grid”; “Standard”; “Jack30”; “Jack50” … only the Jack 30 and Jack 50 show the +0.6 blade.
A blade also appears with the “Standard30x30Grid” and “Standard10-lat” but it begins its rise about 300 years BP.
All of these sets track fairly uniformly until appx 370 yrs BP.
Someone with stats knowledge and an idea of how they created the temp stack data sets will have to decipher what that means – but the “blade” data is there if you plot the data.
The graph I did of the Marcott Temperature Stacks Global data:
http://tinyurl.com/MarcottTempStacks
One more note – per this link from above:
http://www.iceandclimate.nbi.ku.dk/data/Temperature_Reconstruction.pdf/
The Agassiz-Renland data shown in the Marcott data tab is already the 20 year average temperature deviation.
Warren, Thanks for replying. Like you I have an engineering background in computer development, but I also have an interest in most of the sciences.
The reason theat I am became very sceptical about AGW is because the original “Hockey Stick” managed to get rid of the all the variations before the Little IceAge.
See my earlier post: March 11, 2013 at 7:51 pm
The “Hockey Stick” used an algorithm developed by Michael Mann and he claims that his method used proprietary information the he refuses to disclose. Not the way for a scientist to behave!
Zcetek: Thus you seem justified in asking if this is bad science. If it passed the peer review process, it might be useful to see if his Peers raised questions about his statistical methods, and if he answered. Maybe there’s a way to search online for the authors response to this issue. Worth a try perhaps.
…information that he refuses to disclose.
I think that the reviewers found nothing wrong. However, try googling
statisticians slam random global warming hockey stick graph.
Zcetek:
Yes, indeed. Your suggestion was fruitful. There is a peer reviewed paper coming (or perhaps already out) by a penn state statistician that claims that a statistically valid statement that the industrial age hockey stick is different from the prior historical record cannot be made. It’s a Big deal. If the statisticians claims stand the test of peer review, and are generally accepted, then perhaps the next question might be “if the hockey stick is combined with the physics of global warming gas increases in the Industrial Age, and associated modeling, does this combination have validity as a confident statement about AGW?”
Steve Mc has interesting email exchange with Marcott:
http://climateaudit.org/2013/03/13/marcott-mystery-1/#comment-404356
No need to justify study results trumpeted by the media so long as you say they are “not robust” — so remind me of why his article was published in SCIENCE to get all this media hype over results which are “not robust”??
YouAreWrongAgain says:
“You are comparing regional (greenland temps) to a global average temperature reconstruction. This is inherently wrong.”
YouAreWrongAgain. Greenland, Antarctica, and the Arctic all show strong correlation, proving that temperature changes were global in extent.
Thanks to A. Scott for some fascinating insights.
DB,
Both hemispheres appear to correlate well.
In phase, perhaps, but not in amplitude. A cautionary demonstration of the problems of comparing in one one location with another (or global temperature) to make implication about global behaviour. This is the problem with comparing GISP wityh global data – GISP, being localised, is going to show much more variance. Warm periods will be warmer, cool periods cooler (see MWP and LIA for that). Long-term temperature changes in the North Pole are larger than global, too, as we can see in any data set in recent times (eg, UAH – 3 times as much warming as global, same for the geological record).
Not to mention that the GISP graph up top only goes to 1889, and the Marcott graph to 1950. Apples and oranges in several ways.
bmcburney @ur momisugly here.
From what I’ve read, Marcott says current temperatures are warmer than most of the last 2000 years, that what is unprecedented is the rate of change, and that yes, he says that if temps continue to rise they will be warmer than any in the last 11,300 years by 2100.
Do you have a cite to corroborate your interpretation (I’m genuinely curious)?
zctek @ur momisugly here
We are still recovering from the Little Ice Age
Global climate rebounds like a piece of elastic? There is some fixed neutral state around which it oscillates?