Daily temperature observations in Florence at the mid-eighteenth century: the Martini series (1756-1775)

In the framework of the meteorological observations in Florence after the Medici Network (1654-1670), the earliest surviving record by Pietro Gaetano Grifoni (1751-1766) was followed and partially overlapped by the temperature series by Luca Martini (1756-1775), which has been recovered from different sources and analyzed in this paper. Martini series should be divided in two periods, the turning year being 1765, when he changed house, still in Florence. A critical data analysis and the comparison with the Grifoni contemporary series in Florence clarify the thermometric liquid and scale used in the different periods. The reconstruction of the 1756-1775 daily average temperatures is carried out here following a methodology that includes the conversion from the apparent solar time to the Central Europe Time; the transformation from single/double readings to a daily average; the analysis of the hourly temperature variation during the calendar year in the 1961-1990 reference period in Florence; the test made with the snow benchmark; and the correction of the bias due to the local microclimate in the first period. The final series (1751-1775) has been composed combining Grifoni and Martini observations, covers one quarter of the eighteenth century, and constitutes the only surviving outdoor temperature record in Florence. The comparison with other periods from the mid-seventeenth to the early-twenty-first century confirms that in the mid-eighteenth century, the temperature reached the lowest levels and that a marked warming has characterized the most recent decades. Information on the pre-industrial climatology in Florence can be useful for climatic change study.