Surprise in Western Europe: Hot Summer of 1540 Was Significantly Hotter Than Assumed Record Holder 2003
By Dr. Sebastian Lüning and Fritz Vahrenholt
In Western Europe the summer of 2012 was for the most part pretty lousy (see our blog report “When are we ever going to have a summer?“). It wasn’t until mid August that summer showed its stuff and sent thermometers shooting upwards for a few days.
Things were much different in 2003 when Western Europe baked under a heat zone. Back then the heat wave ground everyday living to a halt. During the first two weeks of August new records were set in Great Britain (38.1°C), Germany (40.2°C), and Switzerland (41.5°C) and Portugal (47.5°C).
For a long time it was assumed that the heat wave of 2003 was unique for the last 1000 years, and that there had never been such a heat wave in Europe during that time. It turns out that this was an error. At the end of July, 2012, Oliver Wetter and Christian Pfister of the University of Bern in Switzerland published a new study in the Journal Climate of the Past Discussion. The study shows that temperatures during a Swiss heat-wave summer in the year 1540 was significantly hotter than the summer of 2003. The two scientists write a short summary of their work:
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.”
(Translated with permission by P Gosselin)