Temperature sensitivity of Swiss and British plant phenology from 1753 to 1958

Recent changes in springtime plant phenological records are likely unprecedented and have been attributed to anthropogenically induced temperature change. In Europe, a major synchronous break in phenological time series in the 1980s was found in numerous studies; however, few of these studies put these breaks into a historical perspective. We present evidence from 2 historical plant phenological records from northern Switzerland and the UK from 1753 to 1958. Monthly mean temperature measurements are available for the same regions. We assess whether synchronised changes in temperature and plant phenological records and recent temperature impacts are unprecedented at the end of the 20th century. We compare the temporal evolution of plant phenological spring indices (PPSI) and temperature series, search for common shifts and change-points by applying Pettitt's test and a Bayesian model comparison approach, and discuss changing temperature sensitivity for both localities. Results show that the Swiss records contain half the phenological variability (SD = 5 d), compared to the UK observations, but higher temperature variability in winter and spring. There is a lack of synchronous shifts and one-point-changes in phenological and temperature series prior to 1958 in contrast to the widespread changes in Europe since the 1980s. However, there are indications of phenological shifts between 1840 and 1870 (Pettitt's test) and changes in 1930 (highest change-point probability). Finally, we found a greater and more variable temperature sensitivity of change in the UK PPSI with respect to seasonal temperatures (2 to 15 d °C^-1) than in Switzerland (-2.5 to -5 d °C ^-1).