“Yamalia” tree ring temperature trends.

A new paper from  (Briffa et al., 2013) presents an updated chronology of temperature anomaly series from Siberia (Yamal and Polar Urals) derived from tree ring data. Their results are also discussed on a realclimate post which responds to past criticism and compares the new results to their 2000 result. The original Yamal data caused huge controversy because they showed  a large 20th century warming at northern latitudes – see here. The new results are based on more trees and combine data from both the Yamal peninsula and Polar Urals. The data also have been made available from CRU  website for anyone to download, which is a welcome development. They show 20th century warming but no sharp final peak as in 2000.  I have been looking at the data to study general trends and the “anthropogenic” signal based on different time interval smoothing. Figure 1 shows the derived  yearly  temperature anomalies relative to 1961-1990.

Fig1: Temperature anomalies (relative to 1961- 1990) for  "Yamalia chronology . Red curve is a 30 year FFT filter smooth.

Fig1: Temperature anomalies (relative to 1961- 1990) for “Yamalia chronology . Red curve is a 30 year FFT filter smooth.

First we notice a fairly large large year to year standard deviation which the authors give as ~ 1.4C. A multi-annual averaging reduces the error on trends by approximately 1/sqrt(N). I have used a 30 year FFT smoothing algorithm rather than a running average so as to continue trends to the end points. I chose 30 years for the interval because one often hears that 20-30 years interval is needed to isolate any net CO2 induced warming from short term “natural variations”. The  Briffa et al. paper use a spline fit to the data with a “stiffness” parameter of n-years. They show results for 15 and 100 year filters. The FFT smoothed results for these time periods are shown in Figure 2. Thanks to a courteous reply on realclimate by Tim Osborn I was later able to locate  the code they used for their filter (see below).

Fig 2: Temperature anomalies derived from Yamalia chronology. Blue curve is a 15year smoothing FFT filter. Red curve is a 100y FFT filter.

Fig 2: Temperature anomalies derived from Yamalia chronology. Blue curve is the 15 year smoothing FFT filter and the Red curve is a 100y FFT filter.

I was then able to compare these filters with  the 100 year spline filter presented in the Briffa paper.  This appears to show a significant uptick in the 20th century although they qualify this with the statement. “Note that the smoothed values at the ends of the series are much more uncertain due to the presence of end effects on the spline filters”. They use a Fortran routine for the spline fit to the data with a stiffness factor equal to to 100 years. I was then able to use the same algorithm (see code from this paper) and reproduce their results.  Figure 3 compares the spline 100 year smoothing with that from the 30 year FFT smooth as used in Figure 1. They are remarkably similar and differ only at the end points.

Fig 3a: Comparison of the Briffa 100year spline filter and the 30year FFT filter

Fig 3a: Comparison of the Briffa 100year spline filter (in black) and the 30year FFT filter (in red)

and in detail for the last 300 years.

Fig 3b: Detail for the end point of both fits

Fig 3b: Detail for the end point of both fits

The particular form of the 100y spline filter indeed exaggerates the end points to  imply  net warming of ~2C since 1900. If instead the 30year FFT filter is used then the uptick is reduced to a net warming since 1900 of ~1C.  This also agrees more with their averaged anomalies given in Table 1 of the paper :

1981-2005     Temperature anomaly = 0.9±0.4 deg.C

Conclusion: There is an impressive amount of work presented in the new “Yamalia” paper – (ref 1). The general conclusion that the 20th century shows a warming trend is confirmed but  can no longer be termed as being “unprecedented” since a similar sized peak occurs ~250AD.  The 100 year spline filter used to smooth the data in Fig 13 exaggerates the final uptick. A 30 year FFT filter shows the same trends but avoids this end point problem reducing the apparent uptick by about a half.

References

1. K.R. Briffa, T.M. Melvin, T.J. Osborn, R.M. Hantemirov, A.V. Kirdyanov, V.S. Mazepa, S.G. Shiyatov, and J. Esper, “Reassessing the evidence for tree-growth and inferred temperature change during the Common Era in Yamalia, northwest Siberia”, Quaternary Science Reviews, vol. 72, pp. 83-107, 2013.

2. K.R. Briffa, “Annual climate variability in the Holocene: interpreting the message of ancient trees”, Quaternary Science Reviews, vol. 19, pp. 87-105, 2000.

3. T.M.  Melvina et al. “Time-varying-response smoothing”, Dendrochronologia 25 (2007) 65–69.

 

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13 Responses to “Yamalia” tree ring temperature trends.

  1. feet2thefire says:

    Without the Medieval Warm Period, this study – like all of CRU’s – only goes to show us that the trees used do not represent global climate. Hundreds of climate studies around the world show the MWP. Those that do not show it have to be considered outliers. They should – before publishing – address within the paper what is the reason for the lack of the MWP in the data. THIS happens to be one of those real consensus issues – the MWP DID exist, so why is it not showing up?

    As far as that goes, the Roman Warm Period is also missing. I am under the serious impression that tree rings are unreliable as hell prior to about 1500, so if that is the reason for these missing warm periods, well and good, but do the authors address either one in the paper?

    Steve Garcia

    • Clive Best says:

      I would agree with you that it is surprising how flat the tree derived temperature series is. This means that either
      1) In that remote asian corner of the arctic the MWP didn’t leave any trace or
      2) Tree rings are not a very good proxy for temperature.

      The authors write:

      In the context of this review, if one defines the “Medieval Warm Period” (MWP) very loosely, as one of prolonged high tree growth (and implied summer warmth), assumed to occur sometime be- tween 800 and 1400 CE, neither the TRW or the MXD data, either as previously analysed or as reassessed here, support the conclusion that the MWP is strongly manifest in Yamalia. The exception to this statement is the RCS-processed Polar Urals TRW data produced in Esper et al. (2002) and Cook et al. (2004). The reanalysis of these data here show that the apparent evidence for high tree growth in medieval times in the Polar Urals region (circa 980e1040) was exaggerated due to inclusion of root-collar wood samples.

      They excluded these trees from the study.

  2. Euan Mearns says:

    Clive, simple and instructive. A frustrating thing for me is how the likes of Briffa put so much effort into detailed high quality data acquisition but then spoil this by applying a statistical technique that seems designed to show what they hoped to find. If you had time, I’d be interested to see how a 30 year running average (either trailing or centred) compares with the FFT filter.

    The surprising thing about the data is how uniform the series actually is with no sign of Roman and Medieval warming or Dark Ages and LIA cooling. These events, so clear in NW European historic records, I believe were global (see Plimer’s book Heaven and Earth) but not ubiquitous, i.e. some areas appear more prone to these second order climatic events than others. I dare say large tracts of The Tropics, deserts and evidently N Siberia had fairly stable “climate” for 2000 years whilst others experienced change (either warming or cooling). I believe these second order climatic events are possibly linked to changes in atmospheric circulation, at my latitude (57?N) that means the geometry and behaviour of the Polar Jet.

    Good to see that Osborn responded to your request;-)

    • Clive Best says:

      Thanks for the comments.
      I really think there is a change in attitude among climate scientists. There is more openness and less of the bunker mentality. The result is that we have a more objective chance of understanding climate.

      The new results already show about half the 20th century warming compared to their original 2000 paper – so the “consensus” is shifting.

      There is some (moderate) AGW but in no way is it catastrophic !

      Here is a comparison between Briffa 2013(black) and Briffa 2000(red) . The red numbers show deg.C anomalies. You can see that warming has more or less halved.

  3. Euan Mearns says:

    It seems possible that early 19th Century dip is a Tambora effect….

    (http://berkeleyearth.org/volcanoes/)

    …. account for that and get rid of the 100y spline and you are left with a barely measurable signal for the natural Modern Warm Period cycle.

  4. Kasuha says:

    Regarding Fig.3b, I wouldn’t say FFT filtering is any more reliable than spline. Spline enhances the final trend while FFT smoothing seems to be compensating for it.

    http://www.woodfortrees.org/plot/uah/from:1985/to:2002/plot/uah/from:1990/to:1998/plot/uah/from:1985/to:2002/fourier/low-pass:10/inverse-fourier/plot/uah/from:1990/to:1998/fourier/low-pass:10/inverse-fourier

    • Clive Best says:

      There is no “correct fit”. However a spline with a 100 year stiffness can only be driven by the last 50 years since the next 50 years lies in the future. This gives a problem at both end points. Global temperatures have been flat for about 15 years years and this does not show. I am not saying FFT is “correct” but because the wavelength is 30 years it does better represents recent data.

      • Kasuha says:

        Global temperatures indeed have been flat for last 15 years but there’s not much of that in these data. First they end in 2005. And they’re anything but flat in the last 7 years, Period around 1998 is actually represented by large dip.

        Looking at their 15-year spline I could believe that if they did a 30-year spline, it would also end facing down (and that may be the reason why they didn’t make one). But the “flat” it would be following has nothing to do with the “global flat 1998-today” as that “flat” is all through 1980-2005 and looks more like artifact of noise to me.

        • Clive Best says:

          Yes – you are right. The data ends in 2005 and the trend has nothing to do with global temperature anomalies. However there is a small downturn for the last 5 years of data as shown by the 15 year FFT smoothing in Figure 1.

  5. Clive Best says:

    I seem to have got banned from realclimate again. It seems that only one side of the debate is permitted to express opinons there. So having been pilloried for objecting to the term “deniers” and suggesting that recent climate sensitivity results show that we actually have 50 years to solve low carbon power production – I tried to respond as follows :………

    First I would like to thank Tim Osborne (#32) for pointing me to the spline smoothing algorithm used in the paper. I implemented it and then compared the results to a 30 year FFT filter. The results are surprisingly similar apart from the end effects.

    To respond to some of the other remarks if I may:

    One of the problems of climate science is that it has all become rather too devisive. You are either with us or you are against us. This then leaves little room for any middle ground, which is where I feel I stand. There is AGW but there is also still uncertainty about feedbacks. The models do not make firm predictions on future warming, and recent temperatures are significantly less than those predicted in AR4. It is indeed prudent to reduce CO2 emissions, but drastic action is both dangerous to society and even illogical (IMHO).

    One should never propose a policy without proposing a realistic solution. To cut carbon emissions by say 80% in 30 years is fundamentally impossible through renewable energy. If you take for example the UK, power consumption averages around 40GW rising to a peak demand of ~70GW. This means that nationally we must have an installed capacity of 70GW, – perhaps rising to 100GW if electric transport takes off. However we will always need a 100% reliable base-load of 30GW. Currently there are 3700 wind turbines installed in UK receiving an annual subsidy of ~ 1.2billion. As I write – the sum total power being generated by ALL these turbines combined is 0.3GW (<1% of demand) – see http://www.gridwatch.templar.co.uk/. The maximum power generated on the windiest day this year was 5GW – but only for 2 days. The sums just don’t add up. Suppose we quadruple the number of turbines – ignoring the environmental impact on our small island. This massive effort would be to no avail because instead of 0.3GW we would instead be generating 1.2GW right now – which is still insignificant. Renewables really do cost the earth!

    Current energy policy is miss-conceived and physicists should stand up and say so. Myles Allen recently actually did stand up and say so! The only proven non-carbon energy source remains nuclear power. Nuclear Fusion could also work given the political will.

  6. nuclear_is_good says:

    1. MWP was not a global phenomenon.

    2. You claim

    “The general conclusion that the 20th century shows a warming trend is confirmed but can no longer be termed as being “unprecedented” since a similar sized peak occurs ~250AD.”

    and that is a complete misrepresentation of the situation (and the reason why so-called “skeptics” have zero scientific credibility):

    2a) it is deeply dishonest to make claims about the Earth climate based on a single REGIONAL reconstruction; it is extra-dishonest in the context where now there is extensive evidence that many of the sudden temperature changes in the past (like MWP) have been only REGIONAL with a very, very weak GLOBAL effect;

    2b) the actual GLOBAL reconstructions look like this:

    http://www.ncdc.noaa.gov/paleo/pubs/mann2008/fig3.jpg

    and it is very obvious that the current GLOBAL warming is completely unprecedented in the interval covered by that reconstruction!

    • Clive Best says:

      1. MWP was not a global phenomenon.

      I don’t think we know really that for sure. I am just surprised that the Yamal reconstruction doesn’t show any variation whereas other areas do.

      2. You claim etc…..

      I was actually ONLY referring to the regional reconstruction and did not intend to make any gereralized statements about global temperatures. The original YAMAL paper did claim that recent reconstructed temperatures were unprecedented (in Northern Siberia). The new paper can no longer make that claim. That is all I was saying.

      Regarding global reconstructions – check out my posts on Marcott’s proxies http://clivebest.com/blog/?p=4857 & http://clivebest.com/blog/?p=4833

      Incidentally – if your “nuclear_is_good” implies support for nuclear energy – then I agree with you !

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