Chuine, Isabelle

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French records of grape-harvest dates inBurgundy were used to reconstructspring–summer temperatures from1370 to 2003 using a process-based phenol-ogy model developed for the Pinot Noirgrape. Our results reveal that temperaturesas high as those reached in the 1990s haveoccurred several times in Burgundy since1370. However, the summer of 2003appears to have been extraordinary, withtemperatures that were probably higherthan in any other year since 1370.Biological and documentary proxyrecords have been widely used to reconstructtemperature variations to assess the excep-tional character of recent climate fluctua-tions1–3. Grape-harvest dates, which aretightly related to temperature, have beenrecorded locally for centuries in many Euro-pean countries. These dates may thereforeprovide one of the longest uninterruptedseries of regional temperature anomalies(highs and lows) without chronologicaluncertainties1.In Burgundy, these officially decreeddates have been carefully registered in parishand municipal archives since at least the earlythirteenth century. We used a corrected andupdated harvest-date series4 from Burgundy,covering the years from 1370 to 2003, toreconstruct spring–summer temperatureanomalies that had occurred in easternFrance. To convert historical observationsinto temperature anomalies, we used aprocess-based phenology model for PinotNoir, the main variety of grape that has beencontinuously grown in Burgundy since atleast the fourteenth century5 (for details, seesupplementary information).Our yearly reconstruction is significantlycorrelated (Table 1) with summer tempera-tures deduced from tree rings in centralbrief communicationsNATURE | VOL 432 | 18 NOVEMBER 2004 | www.nature.com/nature 289France6 (correlation coefficient, r0.53), theBurgundy part of a spatial multi-proxy recon-struction2 (r0.69) and observed summertemperatures in Paris7 (r0.75), central England8 (r0.53) and the Alps9 (r0.45).Figure 1 shows two early warm decadalfluctuations: one in the 1380s (0.72 °C)and one in the 1420s (0.57 °C), both abovethe 95th percentile. The warm period of the1420s was followed by a cold period that lasted from the mid-1430s to the end of the1450s (0.45 °C,under the 10th percentile).Our series also reveals particularly warmevents, above the 90th percentile, in the1520s and between the 1630s and the 1680s.These decades were as warm as the end of thetwentieth century. The high-temperatureevent of 1680 was followed by a cooling,which culminated in the 1750s (under the5th percentile) — the start of a long coolperiod that lasted until the 1970s.The inferred anomaly for the summer of2003 represents an unprecedented event. Itwas 5.86 °C warmer than the referenceperiod (1960–89), whereas the next highestanomaly during the whole period was4.10 °C in 1523. This confirms and refinesthe conclusions of previous studies2,10 aboutthe exceptional warmth of the 2003 summerin France.Grape-harvest dates offer the potentialto trace geographical variations in tempera-ture over large parts of Europe and the Middle East over past centuries. This climate, history and phenology synergy canbe used to reconstruct temperatures thatwill substantially add to the long proxy-record databases and provide insight intoregional-scale climate variations.Isabelle Chuine*, Pascal Yiou†, NicolasViovy†, Bernard Seguin‡, Valérie Daux†,Emmanuel Le Roy Ladurie§Grape ripening as a past climate indicatorSummer temperature variations are reconstructed from harvest dates since 1370.YearTemperature anomalies (ºC)–2.0–1.00.01.02.03.04.05.06.01400 1450 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 20000510152   (1901 – 2003)σNumber of stationsFigure 1 April–August temperature anomalies in Burgundy, France, as reconstructed from grape-harvest dates from 1370 to 2003.Yearly anomalies are in black and the 30-year gaussian filter is in yellow. Confidence intervals due to vineyard differences, with an 11-year smoothing, are shaded in blue; these are estimated from the inter-station variability upper 90th and lower 10th percentiles, andare determined when there are more than three available observations in a year. Orange line (number of stations) represents the numberof observed harvest dates for each year, indicating where the confidence intervals are computed. Confidence intervals with two s.e., dueto the regression between observed and reconstructed temperature in Dijon, are in purple. These were obtained by regressing the recon-structed temperature with the observed temperature over 1880–2000. Green horizontal (zero) line is determined from the 1960–89 reference period. Red horizontal lines represent the 2 interval of the reconstructed temperature for the twentieth century (1901–2003).Vertical arrows indicate warm decadal periods (red) above the 90th percentile and the cold trends (blue) under the 10th percentile.A fifteenth-century depiction of the grape harvest from Les TrèsRiches Heures du Duc de Berry, a medieval book of hours.Table 1 Linear correlation coefficients between reconstructed temperaturesSeries Tree rings Multi-proxy Multi-proxy Paris Central England Alps(JJA) (JJA) (AMJJA) (AMJJA) (AMJJA) (JJA)Time range 1750–1975 1500–1998 1659–1998 1787–2000 1663–1992 1760–1998Linear correlation 0.530.09 0.570.06 0.690.06 0.750.07 0.530.08 0.450.09coefficient, r(grape-harvest date)Linear correlation coefficients between temperatures reconstructed from grape-harvest dates in Burgundy and other observed or reconstructed temperaturesare shown. Comparison with temperatures reconstructed from a tree-ring database6 used the closest grid point to Burgundy in the data set. Comparison withmulti-proxy reconstructed temperatures2 used the four closest grid points to Burgundy in the data set. The Paris7, central England8, and Alps9 series areobserved temperatures (instrumental series). Correlations were computed on the common time intervals between two time series. 95% confidence intervalsare shown. JJA, June to August; AMJJA, April to August.V&A MUSEUM/WWW.BRIDGEMAN.CO.UK18.11 brief comms 289 newnew  15/11/04  10:16 am  Page 289© 2004 Nature Publishing Group*CEFE–CNRS, 1919 route de Mende, 34293Montpellier, France †LSCE–CEA–CNRS CE Saclay l’Orme desMerisiers, 91191 Gif-sur-Yvette, Francee-mail: pascal.yiou@cea.fr‡INRA Site Agroparc, domaine Saint-Paul, 84914Avignon Cedex 9, France§Collège de France, 75231 Paris Cedex 05, France1. Pfister, C. Wetternachhersage. 500 Jahre Klimavariationen undNaturkatastrophen 1496–1995 (Haupt, Bern, Stuttgart andWien, 1999).2. Luterbacher, J., Dietrich, D., Xoplaki, E., Grosjean, M. &Wanner, H. Science 303, 1499–1503 (2004).3. Jones, P. D. & Mann, M. E. Rev. Geophys. 42,doi:10.1029/2003RG000143 (2004).4. Le Roy Ladurie, E. Histoire du Climat depuis l’An Mil (ChampsFlammarion, Paris, 1983).5. Robinson, J., Dinsmoor, A. & Smart, R. E. The OxfordCompanion to Wine (Oxford University Press, 1999).6. Briffa, K. R., Jones, P. D. & Schweingruber, F. H. Quat. Res. 30,36–52 (1988).7. Renou, E. Ann. Bur. Centr. Météorol. B 195–226 (1887).8. Manley, G. Q. J. R. Meteorol. Soc. 100, 389–405 (1974).9. Boehm, R. et al. Int. J. Climatol. 21, 1779–1801 (2001).10.Schär, C. et al. Nature 427, 332–336 (2004).Supplementary information accompanies this communication onNature’s website.Competing financial interests: declared none.more than 27% of global land area) in1958–99.For 1950–2000,the trends of globalannual average Tmin for windy, calm and allconditions were identical (0.190.06 °C perdecade; Fig. 1a). So, urbanization has not systematically exaggerated the observedglobal warming trends in Tmin. The same canbe said for poor instrumental exposure andmicroclimatic effects,which are also reducedwhen instruments are well ventilated5.When the criterion for ‘calm’ waschanged to the lightest decile of windstrength, the global trend in Tmin wasunchanged. The analysis is therefore robustto the criterion for ‘calm’. To assess the effectof time differences between the reanalysis4daily-average winds and Tmin, I repeated the analysis using 26 stations in NorthAmerica and Siberia that have hourly or six-hourly reports of simultaneous temper-ature and wind. Again, windy and calmnights warmed at the same rate, in this caseby 0.20 °C per decade.Because a small sample was used, I com-pared global trends for the reduced period1950–93 with published all-conditionstrends for that period based on a sample ofover 5,000 stations6. All differences werewithin 0.02 °C per decade.This robustnessarises because of the spatial coherence of sur-face temperature variations and trends7.The global annual result conceals a relative warming of windy nights in winter in the extratropical Northern Hemisphere(Fig. 1b), mainly in western Eurasia. Theobserved tendency to an increased positivephase of the North Atlantic Oscillation8implies that the windier days in westernEurasia had increased warm advection fromthe ocean9, yielding greater warming. Insummer in the extratropical NorthernHemisphere (Fig. 1c), there was no relativechange in Tmin on windy nights. At that timeof year, atmospheric circulation changes areless influential, but an urban warming signalis still absent. In the tropics, calm nightswarmed relative to windy nights on an annu-al average, but only by 0.020.01 °C perdecade, which is much less than the overalltropical warming in Tmin (0.160.03 °C).This analysis demonstrates that urbanwarming has not introduced significant biasesinto estimates of recent global warming.The reality and magnitude of global-scalewarming is supported by the near-equality oftemperature trends on windy nights withtrends based on all data.David E. ParkerHadley Centre, Meteorological Office,Exeter EX1 3PB, UKe-mail: david.parker@metoffice.com1. Kalnay, E. & Cai, M. Nature 423, 528–531 (2003).2. Peterson, T. C. J. Clim. 16, 2941–2959 (2003).3. Johnson, G. T. et al. Bound. Layer Meteorol. 56, 275–294 (1991).4. Kalnay, E. et al. Bull. Am. Meteorol. Soc. 77, 437–471 (1996).5. Parker, D. E. Int. J. Climatol. 14, 1–31 (1994).6. Easterling, D. R. et al. Science 277, 364–367 (1997).7. Jones, P. D., Osborn, T. J. & Briffa, K. R. J. Clim. 10, 2548–2568(1997).8. Folland, C. K. et al. in Climate Change 2001: The Scientific Basis.Contribution of Working Group I to the Third Assessment Reportof the Intergovernmental Panel on Climate Change (edsHoughton, J. T. et al.) 99–181 (Cambridge Univ. Press,Cambridge, UK, 2001).9. Hurrell, J.W. & van Loon, H. Climat. Change 36, 301–326(1997).10.Diggle, P. J., Liang, K. Y. & Zeger, S. L. Analysis of LongitudinalData (Clarendon, Oxford, 1999).Competing financial interests: declared none.brief communications290 NATURE | VOL 432 | 18 NOVEMBER 2004 | www.nature.com/natureClimateLarge-scale warming is not urbanControversy has persisted1,2 over theinfluence of urban warming onreported large-scale surface-air tem-perature trends. Urban heat islands occurmainly at night and are reduced in windyconditions3. Here we show that, globally,temperatures over land have risen as muchon windy nights as on calm nights, indicat-ing that the observed overall warming is nota consequence of urban development.Observations of the minimum tempera-ture (Tmin) over 24 hours at 264 stationsworldwide since 1950 were expressed asanomalies, relative to the period 1961–90where possible. Coverage of Tmin data wasgood north of 20° N, in Australasia and inthe western tropical Pacific, but poor inAfrica, South America, Antarctica and partsof southern Asia. Reanalysed4 daily-averagenear-surface wind components were used to classify the Tmin anomalies into ‘windy’(upper tercile) and ‘calm’ (lower tercile)conditions. Daily average wind speeds wereused because the timings of temperatureextremes are not known. For stationsbetween 140° E and the dateline, Tmin —which occurs most frequently in the earlymorning — was matched with the previousday’s speed. This is because the early morn-ing in terms of universal time (equivalent to Greenwich Mean Time) is still in the previous day in the Far East.Annual and seasonal anomalies of Tminwere gridded on a 5°5° resolution forwindy, calm and ‘all’ conditions. Coveragewas at least 200 grid boxes (equivalent to1950–1.5–1.0–0.50.00.51.01.5–1.0–0.50.00.51.01.5–3.0–2.0–1.00.0T min (ºC)Year1.02.04.03.01960 1970 1980 1990 2000abcAtmospheric scienceEarly peak in Antarcticoscillation index The principal extratropical atmosphericcirculation mode in the SouthernHemisphere, the Antarctic oscillation(or Southern Hemisphere annular mode),represents fluctuations in the strength ofthe circumpolar vortex and has shown atrend towards a positive index in australsummer in recent decades, which has beenlinked to stratospheric ozone depletion1,2and to increased atmospheric greenhouse-gas concentrations3,4. Here we reconstructthe austral summer (December–January)Antarctic oscillation index from sea-levelpressure measurements over the twentiethcentury5 and find that large positive values,and positive trends of a similar magnitudeFigure 1 Anomalies in Tmin for windy (red) and calm (blue) conditions. a, Annual global data; b, winter data (December toFebruary) for Northern Hemisphere land north of 20° N; c, sum-mer data (June to August) for Northern Hemisphere land north of20° N. The linear trend fits, and the 2 error ranges given inthe text, were estimated by restricted maximum likelihood10,taking into account autocorrelation in the residuals. As expectedfrom the reduced stratification of the boundary layer, Tmin is, onaverage, warmer on windy nights than on calm nights.18.11 brief comms 289 newnew  15/11/04  10:16 am  Page 290© 2004 Nature Publishing Group

Grape ripening as a past climate indicator: summer temperature variations are reconstructed from harvest dates since 1370 /

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