A 1540 ist ein uberaus hitziger somer gewesen, als in manicher zit nehe gehort ader gesehen war.1)

A debatable European summer temperature since 1500

by Hans Erren, Posted 13 August 2004, revised 15 August 2004 (typographical corrections), relocated 1 Jan 2005, second relocation and broken links fixed 5 august 2005

On 5 March 2004 Luterbacher et al published a paper 2) in Science which states that "2003 was by far the hottest summer". The paper contains the following figure, which is reproduced on the website commenting the paper 3)

On several internet forums (eg www.ukweatherworld.co.uk/forum I showed a comparison between the above figure and the Pfister summer index,
arguing that the reconstruction prior to c 1750 has a cold bias. In particular the extraordinary year 1540 is not well represented in the reconstruction of summer temperatures.

On 29 july 2004 I received an email message from Jürg Luterbacher 4). Below I reply one by one to his statements .

"1.) The Pfister data are included in the Luterbacher et al. 2004 temperature reconstructions, thus it cannot be taken for any comparison since it is not independent. This could have been seen from the suppl. online material.
2.) The Pfister data is an index for Switzerland whereas the Luterbacher et al. 2004 reconstructions cover the entire of Europe. Consider local versus continental temperature variability at different time scales. This is all mentioned in the Science paper."

There is a strong correlation of observed annual averaged temperature in central Europe from 1780-2000.

unadjusted Hohenpeissenberg and Vienna, Giss adjusted Basel, my own adjusted De Bilt and Uccle

The correlation is so strong that (carefully homogenised) individual stations may act as predictor for the regional average

same, compared with GHCN and Jones grid cell 0E-15E 45N-55N using data from http://www.co2science.com/temperatures/temps.htm(dataset is now subscription only...)

As such the Pfister index may serve as a predictor for at least the area of Central Europe: Low Countries, Germany, Switzerland and Austria.

"3.) The Pfister data used in the figure is an old version and does not capture the important last decades with a strong warming in Switzerland as well, where would the 2003 summer be? A careful reading of the Schär et al. Nature paper in January 2004 would have been necessary. There it clearly comes out, that the summer 2003 in Switzerland exceeded the 1961-90 mean by around 3decC, corresponding to an excess of up to 5 standard deviations."

I do not question the extreme nature of the summer of 2003, however, using the Pfister index, this summer would rank 3 only in June and August, the 2003 summer index so equals 1536, 1540 1616 and 1947. The first three hot summers are are notably absent in your reconstruction. Compare the year 2003 using the nearby Hohenpeissenberg statistics:

data from GISS and DWD

As well kept observation data exists such as Hohenpeissenberg for the last decade, the absence of Pfister data is not a problem. Furthermore, as all climate indices are bins of fat tail distributed temperature data5). All extreme high values are lumped together in the top bin, extreme values are therefore notably undervalued using climate indices,

"4) The reason of loss of variance on the continental scale in summer temperature is cleary explained and documented in the Science paper."

Indiscriminate use of treering data is demonstrably introducing noise, reducing variance.
As Esper et al. say:

"Die Zusammenfassung von lokalen Jahrringchronologien, die aufgrund der Standardisierungsverfahren keine mehrhundertjährigen Trends enthalten, um niederfrequente Klimaphänomene wie Mittelalterliches Optimum oder Kleine Eiszeit zu studieren (CROWLEY & LOWERY 2000; MANN et al. 1999), sollte vermieden werden."
First there is the memory effect: Extreme years have damaging results lasting for years (Rob Wilson, pers comm) Besides that there is the cold bias: As moisture and temperature both are growth stimulators, a lack of moisture in an extreme warm year will result in retarded growth. As an extreme hot summer in Europe is caused by high pressure blockade, this also prevents rain arriving from the Atlantic. As a consequence, peak years like eg 1540 are not recorded in eg the Larch dataset of Berchtesgaden, whereas a cold summer like 1542 is clearly present.

"5.) Another mistake. The Pfister et al. data are indexed values (ranging from -3 to +3), whereas our y-axes refers to anomalies from the 1901-1995 average. Thus it is useless to compare the two time series anyway."

All proxies are indices, so in your reasoning you also couldn't compare tree rings with temperature? The pfister6) dataset can be calibrated using the rural Hohenpeissenberg7) temperature record:

I also came across the van Engelen Low countries summer index8), which can be calibrated using the revised Labrijn9) series by Van Engelen and Nellestijn10).

Both Pfister and van Engelen agree that the early part of the 16th century was above average, with the year 1540 clearly standing out.

The written records of 1540 tell likewise:

I therefore stick with my conclusion that


I thank prof. Hantsche and Dr Huiskes for providing the reference to the Weinsberg diary, and Aryan van Engelen for giving permission to distribute his revised Labrijn series via my website. Helpful information was received from Stephen McIntyre, Ferdinand Engelbeen, Rob Wilson and prof. Wolfgang Behringer. No funding from any source was sought or received for this research.


1) Herrmann von Weinsberg, Das Buch Weinsberg. Kölner Denkwpürdigkeiten aus dem 16. Jahrhundert Bd. 1 Leipzig 1886 (Nachdruck Düsseldorf 2000) p150&151.
Scan page 150 "Vom Hitzigen Somer"
Scan Page 151 "Angefangen Vil zu drinken"

2) Jürg Luterbacher, Daniel Dietrich, Elena Xoplaki, Martin Grosjean and Heinz Wanner, European Seasonal and Annual Temperature Variability, Trends, and Extremes Since 1500, Science, Vol 303, Issue 5663, 1499-1503 , 5 March 2004

3) European Hotties, World Climate Alert 14b http://www.greeningearthsociety.org/wca/2004/wca_14b.html

4) http://home.casema.nl/errenwijlens/co2/emailluterb.pdf

5) Christopher Essex and Ross McKitrick, Taken by Storm The Troubled Science, Policy and Politics of Global Warming, Key Porter Books (May 2003) , 320 pages

6) Pfister, C., 1993, Historical Weather Indices from Switzerland. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series # 93-027. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. ftp://ftp.ncdc.noaa.gov/pub/data/paleo/historical/switzerland/clinddef.xls

7) Monthly temperature data at Hohenpeissenberg 1781-2003. Sources: GISS, Werner Schulz and DWD http://home.casema.nl/errenwijlens/co2/t_hohenpeissenberg_200306.txt at http://home.casema.nl/errenwijlens/co2/europe.htm

8) AFV Van Engelen, J Buisman and F. IJnsen, 2001, A Milennium of Weather Winds and Water in the Low Countries in: History and Climate Memories of the Future, pp 101-123 Ed. Jones et al, KluwerAcademic/Plenum Publishers http://home.casema.nl/errenwijlens/co2/engelen.xls (1500-2000 only)

9) Labrijn, A., 1945, Het klimaat van Nederland gedurende de laatste twee en een halve eeuw., KNMI mededeelingen en verhandelingen 49.

10) A van Engelen and Nellestijn, JW, 1996: Monthly, seasonal and annual means of air temperature in tenths of centigrades in De Bilt, Netherlands, 1706-1995. KNMI report from the Climatological Services Branch http://home.casema.nl/errenwijlens/co2/LABRIJN.xls

Note added 1 Jan 2005: Since the publication of Luterbacher et al. a new proxy from Pinot grape harvest dates in Burgundy has been published by Chuine et al. Although this data suggest an unprecedented hot summer of 2003, this conclusion does not follow from the data Luterbacher et al use.

update 2 july 2007:
Here is a comparison of Luterbacher Chuine and De Bilt
De bilt is available as monthly observed dataset (1706-2006)
Chuine as AMJJA seasonal modeled temperature (1370-2003)
Luterbacher as MAM and JJA seasonal modeled temperature (1500-2004)

Data sources:
A van Engelen and Nellestijn, JW, 1996: Monthly, seasonal and annual means of air temperature in tenths of centigrades in De Bilt, Netherlands, 1706-1995. KNMI report from the Climatological Services Branch http://home.casema.nl/errenwijlens/co2/LABRIJN.xls extended with giss data (2001-2006) http://data.giss.nasa.gov/gistemp/station_data/
see also:
D. J. Keenan, Grape harvest dates are poor indicators of summer warmth, Theor. Appl. Climatol. 87, 255–256 (2007) DOI 10.1007/s00704-006-0197-9 http://www.informath.org/pubs/TAC06a.pdf