Clim. Past Discuss., 8, 2695-2730, 2012
© Author(s) 2012. This work is distributed
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
An underestimated record breaking event: why summer 1540 was very likely warmer than 2003
O. Wetter1,2 and C. Pfister1
1Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
2Institute of History, Section of Economic-, Social- and Environmental History (WSU), University of Bern, Bern, Switzerland

Abstract. This paper challenges the argument obtained from the analysis of grape harvest (GHD) and maximum latewood density (MXD) data that the 2003 heat-wave in Western Europe was the most extreme warm anomaly in the last millennium. We have evidence that the heat and drought in 1540 known from numerous contemporary narrative documentary reports is not adequately reflected in these estimates. Vines severely suffered from the extreme heat and drought which led vine-growers to postpone the harvest in hope for a rain spell. At the time of harvest many grapes had already become raisins. Likewise, many trees suffered from premature leaf fall probably as a result of a decreased net photosynthesis, as it was measured in 2003. To more realistically assess 1540's spring–summer (AMJJ) temperature we present a new Swiss series of critically evaluated GHD. Basing on three different approaches considering the drought effect on vines, temperatures were assessed between 4.3 °C and 6.3 °C (including the Standard Error of Estimate (SEE) of 0.52 °C) above the 1901–2000 mean which is significantly higher than the value of 2.9 °C measured in 2003. Considering the significance of soil moisture deficits for extreme heat-waves this result still needs to be validated with estimated seasonal precipitation from independent evidence.

Citation: Wetter, O. and Pfister, C.: An underestimated record breaking event: why summer 1540 was very likely warmer than 2003, Clim. Past Discuss., 8, 2695-2730, doi:10.5194/cpd-8-2695-2012, 2012.
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