This paper presents a reconstruction of the summer temperatures over theGreater Alpine Region (44.05°–47.41° N, 6.43°–13° E) duringthe last millennium based on a network of 38 multi-centennial larch andstone pine chronologies. Tree ring series are standardized using anAdaptative Regional Growth Curve, which attempts to remove the age effectfrom the low frequency variations in the series. The proxies are calibratedusing the June to August mean temperatures from the HISTALP high-elevationtemperature time series spanning the 1818–2003. The method combines ananalogue technique, which is able to extend the too short tree-ring series,an artificial neural network technique for an optimal non-linear calibrationincluding a bootstrap technique for calculating error assessment on thereconstruction. About 50% of the temperature variance is reconstructed.Low-elevation instrumental data back to 1760 compared to their instrumentaltarget data reveal divergence between (warmer) early instrumentalmeasurements and (colder) proxy estimates. The proxy record indicates coolconditions, from the mid-11th century to the mid-12th century, related tothe Oort solar minimum followed by a short Medieval Warm Period (1200–1420).The Little Ice Age (1420–1830) appears particularly cold between 1420 and1820 with summers that are 0.8 °C cooler than the 1901–2000 period. Thenew record suggests that the persistency of the late 20th century warmingtrend is unprecedented. It also reveals significant similarities with otheralpine reconstructions.
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