A bi-proxy reconstruction of Fontainebleau (France) growing season temperature from A.D. 1596 to 2000

Abstract

Abstract. In this paper, we develop a new methodology to estimate past changes of growing season temperature at Fontainebleau (northern France). Northern France temperature fluctuations have been documented by homogenised instrumental temperature records (at most 140 year long) and by grape harvest dates (GHD) series, incorporated in some of the European-scale temperature reconstructions. We have produced here three new proxy records: δ18O and δ13C of latewood cellulose of living trees and timbers from Fontainebleau Forest and Castle, together with ring widths of the same samples. δ13C data appear to be influenced by tree and age effects; ring widths are not controlled by a single climate parameter. By contrast, δ18O and Burgundy GHD series exhibit strong links with Fontainebleau growing season maximum temperature. Each of these records can also be influenced by other factors such as vine growing practices, local insolation, or moisture availability. In order to reduce the influence of these potential biases, we have used a linear combination of the two records to reconstruct inter-annual fluctuations of Fontainebleau growing season temperature from 1596 to 2000. Over the instrumental period, the reconstruction is well correlated with the temperature data (R2=0.60). This reconstruction is associated with an uncertainty of ~1.1°C (1.5 standard deviation), and is expected to provide a reference series for the variability of growing season maximum temperature in Western Europe. Spectral analyses conducted on the reconstruction clearly evidence (i) the interest of combining the two proxy records in order to improve the power spectrum of the reconstructed versus observed temperature, (ii) changes in the spectral properties over the time, with varying weights of periodicities ranging between ~6 and ~25 years. Available reconstructions of regional growing season temperature fluctuations get increasingly divergent at the interannual or decadal scale prior to 1800. Our reconstruction suggests a warm interval in the late 17th century, with the 1680s as warm as the 1940s, followed by a prolonged cool period from the 1690s to the 1850s culminating in the 1770s. The persistency of the late 20th century warming trend appears unprecedented.

Multiple tree-ring proxies (earlywood width, latewood width and δ13C) from pedunculate oak (Quercus robur L.), Hungary

“…Consequently the shared common climatic signal emerged in the correlation analysis likely smeared by noncorrelated noise components so common signal is amplified and the noise is quenched when proxies were combined. This agrees with Etien et al (2008) who found more comparable spectral properties with instrumental record in combined proxy. To establish climate reconstruction from these proxies in the future it is useful to get preliminary information about the potential spatial signature of the climate signal.…”

Extreme grape harvest data of Austria, Switzerland and France from A.D. 1523 to 2007 compared to corresponding instrumental/reconstructed temperature data and various documentary sources

“…Pertaining to the temperature reconstructions of Casty et al (2005) and Etien et al (2008), an agreement with our extreme year evaluation can be found in 27% and 31% of possible years, i.e. extreme years according to our criteria, where a respective temperature reconstruction is available and also yields an outstanding value.…”

“…Tables 2 and 3 list 36 years according to the criteria mentioned. We compared the extreme phenological and mean temperature values of these years to each other and to descriptive entries in historical chronicles and manuscripts (Tables 4 and 5) as well as to recent results found by Brázdil and Kotyza (2000), Casty et al (2005), Brázdil et al (2008) and Etien et al (2008). The chronicles of Retz (Puntschert 1894; Löschnig and Stefl 1935) and the accounts of the Retz Buergerspital, considered in addition to the records of Klosterneuburg and Vienna-Buergerspital, constitute a more or less independent possibility of comparison.…”

“…The year 2007, the last year in Table 3, exhibits three positive temperature extremes and a remarkable negative grape harvest extreme in Burgundy of nearly 50 days (5.3σ). Table 5 Comparison of the extreme years of the "historical" instrumental period as listed in Table 3 to diverse documentary sources as well as to extremes defined by Casty et al (2005) and Etien et al (2008) 1 Gulden (fl. )=60 Kreuzer (kr.)…”

“…Casty et al (2005) list of years (1500-2004) with extreme warm mean summer (JJA) and annual mean temperatures exceeding the two-sigma threshold of the 20th century mean, is based on reconstructions (1500-1900, henceforward, CRU temperatures) for the European Alps, using a combination of long instrumental station data and documentary evidence. Etien et al (2008) list of extremely warm reconstructed AMJJAS mean temperatures, exceeding the 1.5 standard deviation of the centennial average, was compiled using δ 18 O records of Fontainebleau (France) latewood cellulose of both living trees and timber and the Burgundy grape harvest records in a bi-proxy reconstruction from A.D. 1596 to 2000. Brázdil et al (2008) dealt with historical observations of the Czech lands before A.D. 1500 and in the 16th to 18th centuries.…”