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)
There are three factors that affect the temperature of the Earth: the intensity of solar radiation, the albedo and the greenhouse effect. Various events that have occurred on Earth (such as volcanoes or the lack of volcanoes just to mention possibility) can affect at least two of these variable. We do not know as well as we do today what was happening over the entire planet say 1,000 or so years ago. So it is therefore quite possible that temperatures were either higher or lower than today and it is also very possibly that we cannot know why because of a lack in relevant information concerning the past. From the Ice Core Record, however, we do know that CO2 levels did not differ then from their preindustrial levels – so just perhaps a warming was caused by lower particulate matter in that atmosphere, a possibility that we cannot assess because of a lack of information concerning that period.
My points is: today we know many times more about existing conditions and events around our planet. We do not have comparable knowledge concerning the past – only bits and pieces in comparison. Thus we should not let our lack of understanding of past climates diminish our confidence in what we do know about our present climate and that of the last 100 years during which modern science bloomed and has provided an unprecedented abundance of information pertaining to climate.
This study is excellent confirmation of what geologists have been saying for years based on the oxygen istotope measurements made by Stuiver and Grootes (1997) on the Greenland GISP ice cores. The past really is the key to the future! In order to understand where climate is heading, we need to know where it’s been. This study should put to rest any doubts about the natural variability of climate, independent of CO2. Most of the warm and cool periods show up well in the ice core record and have been confirmed by historic records, both human and glacial.
if AGW is true, should we not see a drop in warming in Europe following the Black Plague in the 1st half of the 14th Century? Just askin
OK proxies are OK. Bad proxies, such as Mann used, aren’t.
A tad disingenuous, don’t you think? The original hockey stick proxies were twelve trees from one site in Siberia, and the addition of one particular tree created the blade. This paper uses “91 in total, comprising ice-cores, tree-rings (density and width), lake and sea sediments, historical records, speleotherms, and pollen.” The samples were also taken from all over the extra-tropical Northern Hemisphere. Apparently they also did not tack on the observed temperature record when the proxies diverged from what they wanted to see.
I have my doubts about proxies as well; however, when you use so many different kinds from around the globe, I’d hope that you’d get something other than red noise.
“The reconstruction of past climate has improved significantly in the past few years due to the availability of more proxies and better statistical analysis.”
Isn’t this pretty much what you get with Mann’s data when short-centered principal component analysis is not used?
Don J. Easterbrook says:
October 17, 2012 at 8:59 am
This study is excellent confirmation of what geologists have been saying for years based on the oxygen istotope measurements made by Stuiver and Grootes (1997) on the Greenland GISP ice cores. The past really is the key to the future! In order to understand where climate is heading, we need to know where it’s been. This study should put to rest any doubts about the natural variability of climate, independent of CO2. Most of the warm and cool periods show up well in the ice core record and have been confirmed by historic records, both human and glacial.
Former geology student here…. Yep!. It always annoyed me that the climate gurus were so insistent to swipe away all evidence of the past based on sound geologic methodologies, and substitute that with their own brand of short-term /short sighted science. Note that I’m not referring to all of climate science and scientist, but the ones who came to dominate the political landscape… You know the names.
PS. Just wanted to throw this out, that I agree with this post by Gavin. We can only be effective if we make sure we also are skeptical of claims that might favor our skeptic bent.
Fred, your equation’s proof says that 0 = 0, not 3 = 2. Regardless if you divide or multiply by 0. The integer 3 or 2 can be replaced with x = any value, because the value of that integer doesn’t matter. They could even be the same value. Therefore, when your calculation is simplified, it will be 0 = 0. The “logic” your statement tried to use is not logic but is an emotional trick that can be played on simpler minds.
ob says:
October 17, 2012 at 7:31 am
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.
We can be pretty sure that it wasn’t SUVs or power stations 😉 Apart from that, how dare you suggest that something affecting climate might be “not understood”? Remember, the whole of current climate science is built on “it must be … because we don’t know what else it might be”.
In standard published research, inclusion criteria are set to determine which studies merit meta-analysis. That Mann’s study was not is an idictment against it. Burn!
Somehow, all the climate variation up to 1979 or so was natural. Everybody knows that.
Most people think a Warm Globe is a better globe, and they are right. The warming of the globe ended years ago.
Alan the Brit, I fit that demograph, I was lucky enough to attend a grammar school before the left killed them, we were taught, from print (that is why the lefts big heroes burned all the old thought books) about the Romans growing grapes over all of England and the Vikings naming Greenland, and not because they were colourblind ! Then we had lithographs of the thames ice fairs climate changes without our help! I have noticed the lack of common sense in most things green (not the least when I lived in Cornwall and we had one of our usual gales the only thing stationary in the whole county was the wind turbines !)
I think that was kind of his point Pamela. The analogy was that you can prove anything true if you use faulty logic. If I choose to only analyze data with a strong statistical correlation to x, should I be surprised that the logical conclusion is analyzing the data shows it has a strong statistical correlation with x. If I use the 3*0 = 2*0 example to prove 3=2, it is faulty logic. It may be different faulty logic than confirmation bias, but both are still logical fallacies in the end.
ericgrimsrud:
Your post at October 17, 2012 at 8:50 am repeats a falsehood that you know is a falsehood because I have explained the matter to you on two other WUWT threads. I won’t bother to refute it again.
STOP SNOWING THREADS WITH FALSEHOODS THAT YOU KNOW ARE FALSEHOODS.
Richard
Mann doesn’t need to have a twitfest. He can claim
1. New data, new view. Mine was valid with the data I had.
2. If not for my prodding, this new work would not have been done. I initiated Good Things.
3. Yesterday doesn’t matter. Today the situation is different. Yesterday the sun did what human beings are doing today.
4. I have research grants pending to expand on my previous work. Talk to you later when I have gone beyond what doofus has done. I expect validation of what I did.
5. It’s all in my book. Buy another today.
This work is not a problem for Mann, there is always the fall-back of claiming that becasue the data does not cover ever square inch of the planet it means nothing , of course proof of ‘the cause ‘ only requires one magic tree but that is the way climate ‘science ‘ works .
Juraj V. says:
October 17, 2012 at 7:06 am
“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.
Yes… and no need to invoke the special ‘Nature Trick’ as perfected by the IPCC CAGW consensus cabal of climatologists.
It is also becoming obvious that without some serious ‘bending’ of the modern instrument global temperature data-sets that real temperature is much cooler than indicated. We are already over the global peak and on the toboggan ride of the decline. All the extra CO2 seems to have had little or no impact.
The Earth and the sun do it together.
From the paleomagnetic data (far more accurate then tree rings) it is possible to go back 2 millennia with an error of plus/minus 25 years around 0 BC. We don’t exactly know intensity of the solar activity (10Be and C14 are both affected by precipitation – climate factor, with a danger of circular reasoning).
Thus to take an even solar output (Dr. S would approve) than we are left with the paleomagnetics as a single factor giving reasonable correlation
http://www.vukcevic.talktalk.net/LL1.htm
In the more recent times we have good sunspot count and the accurate geomagnetic records (actual measurements initiated by Gauss) from which a more accurate reconstruction is possible:
http://www.vukcevic.talktalk.net/GSC1.htm
ericgrimsrud says:
October 17, 2012 at 8:50 am
[…] My points is: today we know many times more about existing conditions and events around our planet. We do not have comparable knowledge concerning the past – only bits and pieces in comparison. Thus we should not let our lack of understanding of past climates diminish our confidence in what we do know about our present climate and that of the last 100 years during which modern science bloomed and has provided an unprecedented abundance of information pertaining to climate.
Eric, there’s a huge logical disconnect in your statement.
While we may well “know many times more” about current conditions, the conditions that (by your own admission) we DON’T know about from the past are still able to influence climate by as much, if not more, than the recent warming. Since that demonstrate clearly that we DON’T know about all the natural factors capable of producing such warming, the logical conclusion is that information like this seriously damages any confidence we can have about what’s happened recently.
Remember, the only reason the science places such high confidence on the effect of CO2 is because there’s “no natural explanation” for warming of this speed or magnitude. Clearly, if this work withstands scrutiny, there ARE natural explanations. The fact we don’t know what they are, or how they work, doesn’t mean they don’t exist!
My word. The GWPF are on fire.
I want to caution everyone about these results. Besides the fact that there is no such thing as a reasonable temperature proxy that I am aware of, there is a clear pattern of regressomatic sorting in this curve.
The curve is nonsense.
ericgrimsrud says:
October 17, 2012 at 8:50 am
There are three factors that affect the temperature of the Earth: the intensity of solar radiation, the albedo and the greenhouse effect… Thus we should not let our lack of understanding of past climates diminish our confidence in what we do know about our present climate and that of the last 100 years during which modern science bloomed and has provided an unprecedented abundance of information pertaining to climate.
Pretty simplistic way at looking at the climate. You ignore for instance ozone variability. Ozone is warming from direct solar radiation influencing the energy budget of the atmosphere. Ozone can be influenced by natural variation or by solar UV – which can have huge variations even with stable solar radiation intensity.
You ignore the multidecadal natural oscilations like AMO
http://upload.wikimedia.org/wikipedia/commons/b/b4/Atlantic_Multidecadal_Oscillation.svg
or Arctic Oscilation or ENSO.
What do you mean with albedo? Hopefully not an “albedo constant” – see also Earthshine project:
http://www.bbso.njit.edu/Research/EarthShine/
The albedo is variable and we do not know many factors that are influencing it, let alone measure it properly.
Yes we know more then in the past, but our knowledge is far from being complete, as Richard explained you before, repeating again something that has been shown to you to be wrong does not make it right. So trying to understand what caused the climate variability in the past does have a lot of importance for our understanding of what can cause the climate variability today.
Luke, meta-analysis studies set inclusion criteria on study design, not study outcome. That is if they are attempting to be blind to study results. To get a good idea of study criteria for meta analysis done well, visit:
http://ies.ed.gov/ncee/wwc/DocumentSum.aspx?sid=19
That is not a well-taken point. The idea that we “know” more about the present is mistaken. We have more contemporary measurement. The principle of uniformitarianism has not been suspended, so while Lyell argued that we could, based upon observations of present geological processes, understand much about the past, the converse must be true as well. Any processes operating in the past must also be operating now. No physics or chemical laws have been recently suspended in nature.
In order to sort out natural effects from anthropogenic effects, we need to understand HOW those natural effects operate. Any evidence of a recent anthropic effect must be superimposed upon the standing natural signal. The sole justification that Mann and the team had for stating that recent warming was “unprecedented” was founded on the assumption that they had actually discovered the signal of anthropic influence and had a valid physical theory to explain it. This is why in the Climategate emails there is concern that the MWP is not disappearing neatly in new data. If it doesn’t vanish with “better” data, then the argument that current warming is unprecedented is unsupported under the uniformitarian principle. If the rates of change are not importantly different between past and present episodes of warming, then rate changes or speeds are not “unprecedented” either. In short, there is then no demonstrable evidence of an anthropic signal in the climate and climate proxy data.
The fact is that over any geological span of time there is no indication of a strong correlation between CO2 and temperature that indicates a causal linkage, other than evidence that warming oceans discharge CO2 and cooling oceans absorb it, which is what ice core data appears to show during the Pleistocene. At significantly longer or shorter time frames even that mostly vanishes into the effects of other, not so well identified processes at other scales.