Yesterday I highlighted the paper 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 which showed that using a multitude of proxy samples in the norther hemisphere, that:
“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.”
Now another paper, by Esper et al published in the Journal of Global and Planetary Change, shows that not only was the summers of the MWP equal or greater than our current warmth, but that the summers of the Roman Warm Period of 2000 years ago were significantly warmer than today.
Variability and extremes of northern Scandinavian summer temperatures over the past two millennia
Jan Esper, Ulf Büntgen, Mauri Timonen, David C. Frank
Abstract
Palaeoclimatic evidence revealed synchronous temperature variations among Northern Hemisphere regions over the past millennium. The range of these variations (in degrees Celsius) is, however, largely unknown. We here present a 2000-year summer temperature reconstruction from northern Scandinavia and compare this timeseries with existing proxy records to assess the range of reconstructed temperatures at a regional scale. The new reconstruction is based on 578 maximum latewood density profiles from living and sub-fossil Pinus sylvestris samples from northern Sweden and Finland.
The record provides evidence for substantial warmth during Roman and Medieval times, larger in extent and longer in duration than 20th century warmth.
The first century AD was the warmest 100-year period (+0.60 °C on average relative to the 1951–1980 mean) of the Common Era, more than 1 °C warmer than the coldest 14th century AD (−0.51 °C). The warmest and coldest reconstructed 30-year periods (AD 21–50=+1.05 °C, and AD 1451–80=−1.19 °C) differ by more than 2 °C, and the range between the five warmest and coldest reconstructed summers in the context of the past 2000 years is estimated to exceed 5 °C. Comparison of the new timeseries with five existing tree-ring based reconstructions from northern Scandinavia revealed synchronized climate fluctuations but substantially different absolute temperatures. Level offset among the various reconstructions in extremely cold and warm years (up to 3 °C) and cold and warm 30-year periods (up to 1.5 °C) are in the order of the total temperature variance of each individual reconstruction over the past 1500 to 2000 years. These findings demonstrate our poor understanding of the absolute temperature variance in a region where high-resolution proxy coverage is denser than in any other area of the world.
[…]
Discussion and Conclusions
The MXD-based summer temperature reconstruction presented here sets a new standard in high-resolution palaeoclimatology. The record explains about 60% of the variance of regional temperature data, and is based on more high-precision density series than any
other previous reconstruction. Importantly, MXD sample replication prior to the Little Ice Age, during Medieval times and throughout the first millennium AD, is much better than in any other record, and we demonstrated – based on calibration trials using reduced
datasets – that these early sections of the N-Scan record likely still contain useful climate information. This persistent climate signal allowed an estimation of temperature variability throughout the Common Era, revealing warmth during Roman and Medieval times were larger in extent and longer in duration than 20th century conditions.
According to this new record, summer temperatures varied by 1.1 °C among the 14th and 1st centuries, the coldest and warmest 100-year periods of the past two millennia. Temperatures ranged by more than 5 °C among the five coldest and warmest summers of the past 2000 years. These estimates are, however, related to the approach used for proxy transfer, i.e. figures would change, if the calibration method, period, and/or target were modified (Frank et al.,2010b). For example, variance among the 30 coldest and warmest N-Scan summers (Table 3) increases from 3.92 °C to 5.79 °C, if scaling (i.e. adjustment of the mean and variance) instead of OLS regression is used for proxy transfer. These differences between scaling- and regression-based approaches are proportional to the unexplained variance of the calibration model (Esper et al., 2005), and we suggest
smoothing the proxy and instrumental timeseries prior to calibration, as this procedure decreases the unexplained variance in all Scandinavian tree-ring records and thus minimizes the differences between various calibration methods (Cook et al., 2004).
Our results, however, also showed that these methodological uncertainties are dwarfed by the variance among the individual reconstructions.
Differences among six northern Scandinavian tree-ring records are>1.5° in 30-year extreme periods and up to 3 °C in single extreme years, a finding we didn’t expect, as the proxy records: (i) all calibrate well against regional instrumental data, (ii) partly share the same measurement series (or use differing parameters – TRW and MXD – from the same trees), and (iii) originate from a confined region in northern Scandinavia that is characterized by a homogeneous temperature pattern. Since we here calibrated all reconstructions using the same method, between-record differences are likely related to varying data treatment and chronology development methods, measurement techniques, and/or sampling strategies, as well as the remaining uncertainty typical to such proxy data. For example, splicing of MXD data on recent TRW trends as done in Briffa92 might have caused this reconstruction to appear at the lower (colder) end of the ensemble, whereas the combination (and adjustment) of novel digital MXD measurements with traditional X-ray based MXD data as done in Grudd08 might have caused this reconstruction to appear at the upper (warmer) end of the ensemble. Other differences are likely related to the combination of sub-fossil material from trees that grew in wet conditions at the lakeshores with material from living trees growing in dryer ‘inland’ sites. Also varying variance stabilization (Frank et al., 2007) and detrending techniques (Esper et al., 2003) in association with temporally changing sample replications and age distributions of the underlying data (Melvin, 2004) likely impacted the variance structure of the long-term records and consequently the absolute levels of reconstructed temperatures.
Between-reconstruction variance as revealed here represents a pending challenge for the integration of proxy records over larger regions and the development of a single timeseries that represents the Northern Hemisphere (e.g., Mann et al., 2008), for example. The composition of such records commonly relies on the calibration statistics derived from fitting regional proxy records against instrumental data (D’Arrigo et al., 2006). However, the records analyzed here would all easily pass conventional calibration-based screening procedures. Yet our analysis revealed that choosing one Scandinavian record instead of another one can alter reconstructed temperatures by 1.5-3 °C during Medieval times, for example. On the other hand, consideration of all records presented here would likely promote a less variable climate history, as the combination of diverging records tends to reduce variance in the mean timeseries (Frank et al., 2007). If such a mean is then combined with instrumental data covering the past 100–150 years, this approach might facilitate hockey stick-shaped reconstructions (Frank et al., 2010a). This seems to be a tricky situation in which expert teams including the developers of proxy records might need to be involved to help assessing timeseries beyond the typical ranking based on calibration statistics.
Our results showed that introducing an improved temperature reconstruction does not automatically clarify climate history in a given region. In northern Scandinavia, we now arrive at a situation where a number of high-resolution proxy records – all passing classical calibration and verification tests – are available within a confined region that is characterized by homogeneous temperature patterns. These records, however, differ by several degrees Celsius over the past two millennia, which appears huge if compared with the 20th Century warming signal in Scandinavia or elsewhere. We conclude that the temperature history of the last millennium is much less understood than often suggested, and that the regional and particularly the hemispheric scale pre-1400 temperature variance is largely unknown. Expert teams are needed to assess existing records, and to reduce uncertainties associated with millennium-length temperature reconstructions, before we can usefully constrain future climate scenarios.
Full paper here (PDF -link fixed)
h/t to WUWT reader Gordon Pye and Tory Aardvarrk
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icarus62:
Your post at October 18, 2012 at 1:53 pm is such a total load of baloney that I copy all of it to ensure that nobody thinks I am addressing anything out of context. It says to me
We do NOT “know that anthropogenic global warming is accelerating”. Indeed, nobody has managed to detect any AGW let alone measure its rate.
There are NO observed effects of anthropogenic global warming (AGW) “accelerating”. The recent reduction in Arctic ice certainly is NOT an indication of AGW “accelerating”. Indeed, polar caps are NOT “reducing worldwide”. Antarctic ice is growing and very recently achieved a record amount. If Arctic ice decline is evidence that AGW is “accelerating” then the growth in Antarctic ice to its recent record level is evidence that AGW is NOT happening.
The changes to glaciers et al. only indicate that the Earth has been recovering from the Little Ice Age (LIA) back towards the temperatures of the Medieval Warm Period (MWP). The glaciers started to recede centuries prior to any significant AGW.
Global warming cannot “continue” because it stopped 16 years ago. Indeed, very recently there has been global cooling. At issue is whether the present flat-line of global temperature will end with resumption of warming towards the temperatures of the MWP or is a transition to cooling towards temperatures of the LIA. I suggest you pray for the benefits of warming and not the horrors of cooling because prayer is the only thing we can do to affect either.
Importantly, all your suggested activities are outrageous and horrific. For example, if you think “population control” is desirable then there is only one way you can reduce the size of the population without harming others and that would only reduce it by one. Perhaps you will work out what it is and do what you say is required.
Richard
Best I can tell from the responses here, the party line is, in essence: “It’s different this time”
icarus62 says:
“We know that anthropogenic global warming is accelerating, as are many of its consequences such as disappearing Arctic sea ice and melting glaciers and ice caps worldwide, validating many decades of predictions by climate scientists.”
So many false statements in just one sentence.
Luval wrote: “Prediction for climate changes in the next 30 years are quite accurate . . .”
You must be a wizard. I don’t know why we even bother to have models if you have magical powers that let you see the future, Why don’t you be the climate king and just tell us what to do.
Seems to be desperation from the warmistas, judging from the mount of new trolls pouring in with the usual inane comments. The missing heat seems to have been discovered. It’s all turning up at the warmistas. Feeling the heat, losers?
richardscourtney says:
October 18, 2012 at 12:11 pm
The Null Hypothesis says it must be assumed a system has not experienced a change unless there is evidence of a change.
The Null Hypothesis is a fundamental scientific principle and forms the basis of all scientific understanding, investigation and interpretation. Indeed, it is the basic principle of experimental procedure where an input to a system is altered to discern a change: if the system is not observed to respond to the alteration then it has to be assumed the system did not respond to the alteration.
It was Charles Darwin who said that doing science without a hypothesis is like going to a gravel pit and counting the stones in it. I think the principle extends to the null hypothesis also – for every hypothesis there is the reciprocal null hypothesis. A “hypothesis” is in a sense an epiphenomenon, the counter null hypothesis actually has more reality and substance. A “hypothesis” is established by refuting the corresponding null hypothesis.
The null hypothesis flows directly from Karl Popper’s assertion that science can only be deductive, not inductive. Popper states this in a way that sounds extreme and dogmatic (“there are no inductive inferences, any that appear to be so are illusory”) but the logic he develops around this seems unassailable. You cannot prove a hypothesis, but you can disprove a null hypothesis.
(See “Conjectures and Refutations” by Popper.)
Esper et al. – YET ANOTHER paper that shows the overwhelming ordinariness of our recent climate history of the last century or two.
icarus62 says:
October 18, 2012 at 1:53 pm
so the big money needs to go on adaption to the growing climate chaos, disaster management, population control and so on.
And there you have the money quotes from the Warmistas. I especially like the population control one.Stalin,Mao,Pol Pot,etc would be so proud.
mods….anyway to track just where all these canned eco-cultists are showing up from?
Holy Roman Empire.
Jan Esper continues to do some of the best Paleo work I’ve seen.
Seems that Icarus has forgotten, (again) the advice he was given by his father. The wax must be softening quickly…
I do not see how demonstrating that in the northern Scandinavia ,summer temperatures 1000 years or 2000 years ago were warmer than Scandinavia’s current warmest summer ‘links’ to Global warming (Or cooling for that matter) as this article is supposedly suggesting. There had always been variations. Indeed there are millenia that were warmer than today but this does not necessarily mean that our current warming situation (If we all agree there is warming after all) is totally natural and nothing of concern. To the comments that are questioning the validity, representiveness and accuracy of this data from tree trunks, I say even though IPCC might not take this warnings as an alarm, truth almost always come from the corners least expected and therefore we must treat every data with equal caution and consideration. A cold millenium or two ( little Ice age or current era) after a warmer one ( Roman era) suggests nothing about Global warming. We need to do a lot of maths and look at trends, general trends not mere variation.
Just because there were warmer summers in the past doesn’t mean it’s OK to have warmer summers now. 1000 and 2000 years ago if there was increased flooding in rural areas, less people would have been affected. In the Roman era, the population was estimated to be 200 million (source). We are currently over 7 Billion… that means there are 35 times more people, taking up 35 times more space, with an even larger than 35 times bigger carbon footprint. During the Roman era, it can be argued that the warming was part of a natural cycle, but one cannot argue now that our massive increase in GHG emissions is causing the global temperature to rise, which will result in more extreme weather events, and as there are now more people, more people will be negatively affected, and in turn it will affect everyone, whether you’re safe in your home in Switzerland or living in a shack in India.
Sources:
http://www.vaughns-1-pagers.com/history/world-population-growth.htm
Interesting historical parallel with the history of the Roman Empire, which reached its peak around the first century AD and fell apart completely in the fifth.
Of course, I am not suggesting that climate drove the entire history of the Empire. But, it was largely agrarian-based economically. If the seasons got progressively colder, yields would have fallen. Nothing like a bit of hunger among the peasantry to undermine support for the rulers.
phlogiston:
At October 18, 2012 at 9:10 pm, in response to my explanation of the Null Hypothesis at October 18, 2012 at 12:11 pm, you conclude saying
Yes. That is why my explanation says
Of course, and as you say, one needs to decide the observation which would indicate the system under study has changed. And my explanation includes that for consideration of AGW saying
Richard
Muzi:
Your muddled and illogical post at October 19, 2012 at 1:12 am concludes saying
Maths done. Trends analysed.
There has been NO global warming for the last 16 years and a very slight cooling trend over very recent years. Global warming is “an ex-parrot”.
Next false scare please.
Richard
Matt:
Your post at October 19, 2012 at 2:10 am is an outrageous call for genocide on an unprecedented scale. I quote it all because it is so extreme that people reading a rebuttal of it could think the rebuttal exaggerates.
Firstly there is no evidence – none, zilch, not any – that anthropogenic GHG emissions are causing any global warming and much evidence refutes it; e.g.
Missing ‘Hot Spot’
Missing ‘Trenberth heat’
Missing ‘committed warming’
No warming for the last 16 years while the emissions have continued to increase
etc..
And the anthropogenic GHG emissions are NOT “massive increase in GHG emissions”. Nature emits 34 molecules of CO2 for every molecule emitted by all human activities.
Also, “35 times more people, taking up 35 times more space, with an even larger than 35 times bigger carbon footprint” is all trivial on a global scale. Humans inhabit a small part of the fifth of the world which is not covered in water.
But, as you say, “one cannot argue now that our massive increase in GHG emissions is causing the global temperature to rise, which will result in more extreme weather events,”. One cannot argue it because it all baloney.
(a) anthropogenic GHG emissions are NOT causing the global temperature to rise: it has not risen for the last 16 years
and
(b) there is reason to think that if global temperature were to rise then that would REDUCE both the frequency and severity of extreme weather events because it would reduce the temperature differences which cause weather events.
Importantly, reducing “our carbon footprint” would be the greatest crime against humanity which is imaginable. It would probably be worse than thermonuclear war.
People die when starved of adequate energy supply because all human activity requires adequate energy supply for
1. production of food,
2. manufacture of goods,
3.provision of services,
4. heating and cooling,
5. cooking, and
6. transport of food, goods and services from where they are produced to where they are needed.
At present adequate energy supply is provided by fossil fuels and nuclear power. The power available from wind, solar and muscles was abandoned when the greater energy intensity in fossil fuels became available by use of the steam engine. The greater availability of energy enabled more people to survive so human population growth dramatically accelerated.
Human population is now conservatively estimated to be 6.6 billion and continues to grow. The population is estimated to peak around the middle of this century when it will be at least 8 billion.
That additional 2.4 billion people requires additional energy supply to survive. And the only possible sources of the needed additional energy are fossil fuels and nuclear power. A return to wind, solar, animal power and slavery cannot provide anywhere near enough energy.
Most of the needed additional energy must be from fossil fuels because not everything can be powered from the end of a wire. And the use of fossil fuels increases GHG emissions with resulting increase to “our carbon footprint”.
So, holding our “carbon footprint” at its present level would kill at least 2.4 billion people, mostly children, in the next few decades. And reducing our “carbon footprint” would kill more millions or billions.
In other words, on the basis of falsehoods which you assert you are advocating an atrocity which would make relatively trivial the combined activities of Gengis Khan, H1tler, Stalin and Pol Pot.
As someone much wiser than me once said, I say to you, “Get thee behind me, Satan”.
Richard
johanna:
re your post at October 19, 2012 at 2:17 am.
Learn some history before posting such bollocks.
Richard
Any increase or decrease in observed global temperatures are a very likely and inherent part of the climate system given the multitude of external (e.g. solar flares) and internal (e.g. volcanic eruptions) climate forcing factors that influence such temperatures.
What has changed is the growth of the human population and the extent of our influence in the atmosphere that surrounds and, together with the geosphere and hydrosphere, supports human life. Therefore any change in say internal forcing factors, such as the undeniable increase in greenhouse gases, will illicit a response on proportions that weren’t previously measurable i.e. across geographic space largely because these changes affect A LOT more of the population.
Our capacity to adapt to changing patterns can only go so far and like other species with which we share our complex planet a change in habitable space (our distribution) will be affected.
Let’s not forget the spread of the ranges of species that would occur given an increase in temperatures reported by the bodies such as the IPCC. The range of malarial-vector mosquitoes is closely linked to temperature distributions, as this increases so will the spread of malaria areas affecting more and more people throughout the globe.
We have it in our capacity to acknowledge and take measures against the very real threat of a changing climate, be that warming or cooling. The evidence available today certainly shows a general warming trend and the increased occurence of extreme weather certainly warrants adaptive attention.
Perhaps it is time to adopt the PRECAUTIONARY PRINCIPLE wholeheartedly for the benefit of all mankind. After all, the cost of ignoring the issues far out way any (if there are any) negative implications of taking long-term sustainable measures to mitigate and adapt to changes in the climate system.
Richard: The latest 16-year warming trend is 0.12°C per decade according to GISTEMP. Here are some other recent 16-year trends in GISTEMP:
1982 to 1998: 0.15°C per decade
1983 to 1999: 0.18°C per decade
1984 to 2000: 0.19°C per decade
1985 to 2001: 0.17°C per decade
1986 to 2002: 0.16°C per decade
1987 to 2003: 0.17°C per decade
1988 to 2004: 0.20°C per decade
1989 to 2005: 0.21°C per decade
1990 to 2006: 0.23°C per decade
1991 to 2007: 0.26°C per decade
1992 to 2008: 0.28°C per decade
1993 to 2009: 0.21°C per decade
1994 to 2010: 0.17°C per decade
1995 to 2011: 0.14°C per decade
1996 to 2012: 0.12°C per decade
Over the whole period of 30 years, the warming trend is 0.17°C per decade, but 16-year trends range from 0.12 to 0.28°C per decade (average 0.19°C per decade) – there is simply too much short-term variability to claim that a 16-year trend of 0.12°C per decade represents a genuine reduction in global warming. If the 30-year trends started to show a significant decline, then we could agree that global warming was slowing down, but that hasn’t happened.
As Feynman said, the easiest person to fool is yourself – don’t get bogged down in short-term climate variability, and miss the wood for the trees (so to speak).
The geological record reveals great fluctuation in Earth’s climate throughout time. One must keep in mind however that just because the climate alters due to natural means (solar variability, volcanism and changes in the oceans conveyor belt for example) it does not in any way diminish the pressing impact of anthropogenic influenced climate change. It is clear that scientists have not fully understood the magnitude of man made influences vs natural influences on climate, but it is clear that we indeed influence climate. While how much we influence future climate is up for debate, it becomes an ethical debate as to whether a bit of uncertainty is enough for inaction. Regardless of the degree of influence we have on future climate, the fact that we do indeed change the climate should be enough to set forth mitigation policies. A better understanding of past climate such as is put forth by this paper will only help scientists differntiate man made vs natural forcings as well as to help better predict future climate.
Definition of ‘Null Hypothesis’
A type of hypothesis used in statistics that proposes that no statistical significance exists in a set of given observations. The null hypothesis attempts to show that no variation exists between variables, or that a single variable is no different than zero. It is presumed to be true until statistical evidence nullifies it for an alternative hypothesis.
Investopedia explains ‘Null Hypothesis’
The null hypothesis assumes that any kind of difference or significance you see in a set of data is due to chance.
For example, Chuck sees that his investment strategy produces higher average returns than simply buying and holding a stock. The null hypothesis claims that there is no difference between the two average returns, and Chuck has to believe this until he proves otherwise. Refuting the null hypothesis would require showing statistical significance, which can be found using a variety of tests. If Chuck conducts one of these tests and proves that the difference between his returns and the buy-and-hold returns is significant, he can then refute the null hypothesis.
Read more: http://www.investopedia.com/terms/n/null_hypothesis.asp#ixzz29kRpofpP
Null Hypothesis: Null Hypothesis is one of the confusing terms that most students really struggle with, so get comfy, grab a cup of coffee, and we’ll get through it together….
The simplistic definition is that the null hypothesis is the opposite of the hypothesis being tested. The researcher suspects the hypothesis to be true (and thus is doing research to support the hypothesis), but the null hypothesis is the hypothesis the researcher tries to disprove. The researcher never proves or accepts the null hypothesis, but can only reject it or not reject it. Confused? How about an example?
Hypothesis: Roses exhibit greater rate of growth when planted in soil rather than compost.
Null Hypothesis: Roses do not exhibit greater rate of growth when planted in soil rather than compost.
Ok, these are lame, but they make the point. Let’s say the researcher collects and analyzes the data, and the results are statistically significant at the 99% level (the data show that roses do grow better in soil with 99% confidence) – in this case, the researcher would reject the null hypothesis and accept the hypothesis.
Read more: http://www.alleydog.com/glossary/definition.php?term=Null%20Hypothesis#ixzz29kTmKvZq
Matt says:
Just because there were warmer summers in the past doesn’t mean it’s OK to have warmer summers now.
The problem is, if it was warmer in the past, then we are well within the limits of natural variability. If you think warmer summers aren’t OK, and the warming is completely natural, what can we possibly do about it?
Oh, that’s right – this time it’s different.
Johanna
There was a lot of infighting in the Western Roman Empire and they left themselves weak and open to attack from outsiders and so called allies. The Eastern Romam Empire at the other end of the Mediterranean contnued sucessfully for another 1000 years.
We are fortunate to have their climate references and can indeed see considerable fluctuations in climate and the means with which they coped with it
tonyb