Mike Mann will have a twitfest on Twitter trying to knock this one down. Data from 91 Northern Hemisphere proxies was used to reconstruct temperature. See reconstruction graph (figure 5) below.
Via The GWPF:
A new paper, looking back at the climate of the past two thousand years, published in the journal “Climate of the Past,” will either cause something of a stir, or provide confirmation of what some regard as having already emerged from the peer-reviewed scientific literature. The title of the paper is, “The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability,” by B Christiansen of the Danish Meteorological Institute and F C Ljungqvist of Stockholm University.
The climate of the past few hundred years is of clear importance because it allows scientists to put today’s warm period into context, and provides some evidence of the influence of the quantity of greenhouse gasses that mankind has injected into the atmosphere. In much literature and during many debates statements to the effect that it is warmer now than it has been for thousands of years are frequently used.
As the authors point out the major problem with reconstructing the climate of the past few thousand years is that the so-called instrumental period – for which we have direct measurements – only stretches back as far as the middle of the 19th century. To overcome this researchers in this paper compile an impressive number of temperature proxies situated in the extra-tropical Northern Hemisphere. There are 91 in total, comprising ice-cores, tree-rings (density and width), lake and sea sediments, historical records, speleotherms, and pollen. All of them go back to 1500 AD and 32 go back as far as 1 AD.
The reconstruction of past climate has improved significantly in the past few years due to the availability of more proxies and better statistical analysis. The authors acknowledge this and point out the differences that are emerging from the reconstructions conducted about a decade ago. They mention two such reconstructions performed by Michael Mann that they say, perhaps typically for the period, show little variability. They add they display, “little evidence for previous temperature anomalies comparable to those of the 20th century.” The authors conclude that previous climate reconstructions “seriously underestimate” variability and trends in the climate record of the past two millennia.
This new analysis shows that the warming we have seen in the late-20th century is not unprecedented, as can be seen in figure 5 (from the paper). Seen in the reconstruction is a well-defined peak of temperature between 950–1050 AD. They also find that the first millennium is warmer than the second.
The researchers conclude:
“The level of warmth during the peak of the MWP (Medieval Warm Period) in the second half of the 10th century, equaling or slightly exceeding the mid-20th century warming, is in agreement with the results from other more recent large-scale multi-proxy temperature reconstructions.”
Ljungqvist et al. also show that, “on centennial time-scales, the MWP is no less homogeneous than the Little Ice Age if all available proxy evidence, including low-resolution records are taken into consideration in order to give a better spatial data coverage.”
In conclusion this impressive piece of research makes a significant contribution to a growing body of evidence that both the global extent of the MWP, and the temperature was similar, or even greater than the Current Warm Period, even though the atmospheric CO2 concentrations today are some 40% greater than they were during the MWP.
Some argue that without anthropogenic greenhouse gasses the world would have cooled in the past few decades. That might be the case, but the statement that it is warmer now than it has been for thousands of years is untrue. The rate of warming seen recently is also not unprecedented.
In the context of climate sensitivity – the real world climatic reaction to increasing greenhouse gasses – and climate model uncertainty, it is an interesting question to ask: if Nature alone in the past can produce temperatures like those we see today, why can’t she do so again?
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The link to the journal is here. Abstract below.
The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability
B. Christiansen1 and F. C. Ljungqvist2
1Danish Meteorological Institute, Copenhagen, Denmark
2Department of History, Stockholm University, Stockholm, Sweden
Abstract. We present two new multi-proxy reconstructions of the extra-tropical Northern Hemisphere (30–90° N) mean temperature: a two-millennia long reconstruction reaching back to 1 AD and a 500-yr long reconstruction reaching back to 1500 AD. The reconstructions are based on compilations of 32 and 91 proxies, respectively, of which only little more than half pass a screening procedure and are included in the actual reconstructions. The proxies are of different types and of different resolutions (annual, annual-to-decadal, and decadal) but all have previously been shown to relate to local or regional temperature. We use a reconstruction method, LOCal (LOC), that recently has been shown to confidently reproduce low-frequency variability. Confidence intervals are obtained by an ensemble pseudo-proxy method that both estimates the variance and the bias of the reconstructions. The two-millennia long reconstruction shows a well defined Medieval Warm Period, with a peak warming ca. 950–1050 AD reaching 0.6 °C relative to the reference period 1880–1960 AD. The 500-yr long reconstruction confirms previous results obtained with the LOC method applied to a smaller proxy compilation; in particular it shows the Little Ice Age cumulating in 1580–1720 AD with a temperature minimum of −1.0 °C below the reference period. The reconstructed local temperatures, the magnitude of which are subject to wide confidence intervals, show a rather geographically homogeneous Little Ice Age, while more geographical inhomogeneities are found for the Medieval Warm Period. Reconstructions based on different subsets of proxies show only small differences, suggesting that LOC reconstructs 50-yr smoothed extra-tropical NH mean temperatures well and that low-frequency noise in the proxies is a relatively small problem.
The paper is not paywalled and be read in its entirety here. (PDF)
Notice that the bulk of warming occurred in the first half of 20th century and present warm peak is not different from that in 1940s. Sorry, no anthropogenic fingerprint there..
When I was twelve, I knew it was warmer a thousand years ago than it is now..
But then, I was reading the Viking sagas. Perhaps Michael Mann should do likewise.
“That might be the case, but the statement that it is warmer now than it has been for thousands of years is untrue. The rate of warming seen recently is also not unprecedented.”
That one tree Mann loves so much has a great deal to answer for!
Nice big dip at AD540 – should please Mike Baillie and catastrophists.
Reconstruction of the extra-tropical NH mean temperature (C) based on the gray-shaded proxies in Table 1 reaching back to at least 300 AD. Calibration period 1880–1960AD. Only proxies with positive correlations and a p-value less than 0.01 are used.
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This still leaves open the question of selection bias which has been shown to create hockey sticks.
Just because a proxy correlates during the period 1880-1960 doesn’t mean it will continue to correlate outside this period. The correlation could simply be accidental, which means that the selection process is amplifying the noise instead of reducing it.
This was the criticism of the Mann methodology and the more recent Southern hemisphere hockey stick that was withdrawn prior to publication after the problems were identified on Climate Audit.
It is a statistical error that is well recognized in fields outside of climate science, such as statistics. Formally it is known as “Selection on the Dependent Variable”. It is a statistical no-no. It is like division by zero, you can prove anything true. 3/0 = 2/0, therefore 3=2.
correction:
It is like multiplication by zero, you can prove anything true. 3*0 = 2*0, therefore 3=2.
A slightly different way to look at
http://www.colderside.com/Colderside/Temp_%26_CO2.html
with the same result. – – – All you have to do is juxtapose the 280 ppm CO2 flatline with land temperature over the past thousand years. Then it is stunningly obvious that the any linkage between temperatures and CO2 is clearly absent from the recent record.
Mike should have had his twitfest back in April when this article actually came out :-p
new? if you call 6 to 12 months new. Did Mann try to knock the previous C&L or L papers down? I can’t remember? C&L12 isn’t too different from some of the previous reconstructions. Furthermore, if you look at their Figures 2,3 and 10, you see that their results are far from claiming “universal northern hemispheric warmth”. You also see the obvious mismatch with the observations. The most important point of the paper is: It shows that we really don’t understand the origin of the century of (regionally rather extreme) warmth at the change of the millennia.
Inconvenient.
it is a shame that we are only now rediscovering what we already knew decades ago. Climate is hugely variable with these apparent peaks and troughs and todays temperatures are nothing out of the ordinary.
We must assume that the non warming of today over historic temperatures is because the concentration of co2 ceases to matter after around 280/300 ppm. In other words that apears to be the high spot of the logarithmic curve.
tonyb.
Their plot looks much like what I found in just the ice core data. See slide 49 in http://www.kidswincom.net/climate.pdf. Atributing the temperature rise since 1850 solely to anthropogenic emissions is not statistically probable because the rise in anthropogenic emissions is covarient with natural longterm cycles that the authors are attempting to identify. Quantifying the relative contributions is more difficult. http://www.retiredresearcher.wordpress.com.
That’s easy to sort out. The crew at SkS have a little trick to deal with misbehaving MWPs; see what they did to Ljungqvist’s last effort.
One thing that strikes me about this proxy is the speed of the temperature increase 1000 years ago. We have been told that it is not just the warming but the rate of increase that is alarming.
It seems from the graph that the warming 1000 years ago, looks just like the modern warm period.
Anybody who read history either professionally, or as an ameteur, or was taught it in schools, who is 40+ years of age, knows it was warmer a thousand years ago than it is today! People have short memories indeed! It is really something when in a 16 year old’s science GCSE paper they get a multiple choice question about what burning fossil fuel causes, of course the box against “Global Warming” is the required answer. Frankly, the question is generally irrelevent as the question is one of many in the examination, & is indeed only there to promote the propaganda of AGW into vulnerable & easily shaped young minds! In this country brainwashing with political propaganda is illegal, just don’t tell the Guvment that & never mention it to the 13 year long Imperiously Socialist New Labour from 97-2010!
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The level of warmth during the peak of the MWP (Medieval Warm Period) in the second half of the 10th century, equaling or slightly exceeding the mid-20th century warming….
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I don’t think that’s going far enough. Greenland & other N Atlantic regions (at least) were much warmer during the MWP than now.
If you look at it like a stock chart, there is a range-bound downward trend line. Around 1950 the curve breaks the trend and escapes the range. If I were a momentum investor, I’d buy that stock.
So…proxies are ok now.
There is so much anecdotal evidence of both the Medieval Warm Period and the Little Ice Age, both in contemporaneous accounts and literature, that Mann’s work should have been called into question just based on that evidence. The fact that it wasn’t, the fact that it was embraced whole heartedly by the majority of climate scientists and the greenie leftists, shows just how unscientific climate science is.
But they didn’t use the sacred bristlecones, and nor did they process the data with the holy algorithm of Mann.
As others have mentioned above, it is too bad that what we used to know is now a revelation in the context of the false Mannian climate perspective that is the alleged current consensus..
Ooooops. Yamal is there and prominent. Fortunately, the methodology apparently doesn’t mine for hockey sticks does’it? I’m wondering what weights is assigned to Yamal?
I bet Craig Loehle is pleased with this study. High 5s.
Juice says:
October 17, 2012 at 8:05 am
So…proxies are ok now.
Proxies and anecdotal evidence are all that we have and both have their limitations. Yet, using a wide variety of proxies over a wide area with good statistical analysis makes proxies more valuable and scientifically meaningful. When they match with the anecdotal evidence, proxies become even more reliable.
The problem with Mann and the Team is not that they used proxies, but that they primarily relied on tree rings and very bad statistical analysis. Plus they simply dismissed the anecdotal (historical accounts) evidence that indicated they were wrong. Oh…and Mann was extremely arrogant and obnoxious in defending his horrible science work!
I recall a divergence controversy on the location of Viking North America settlement during the MWP based on narratives. Their estimate of latitude, they sailed by latitude, put the settlement in Massachusetts or maybe a little north. The description of the flora and fauna put it in New Jersey or a little south. This difference has never been reconciled which made the search for physical evidence of the settlement even more difficult.