Air temperature changes in Wrocław (southwestern Poland) in 1773–1781 based on recently discovered early-instrumental meteorological measurements

Abstract. The article presents a description of an early-instrumental series of meteorological measurements made in Wrocław (SW Poland) in 1773–1781 and its importance for improving knowledge of climate and climate change in Silesia, Poland, and Central Europe. The series is the third-oldest available for Wrocław and is based on observations made by Johann Ephraim Scheibel on the premises of the Gymnasium that belonged to the Church of St. Elizabeth (central Wrocław). Meteorological observations of air temperature were made three times a day: in the morning immediately after sunrise; in the afternoon between 1 and 2 o'clock; and in the evening 1 or 2 h after sunset and were published in the newspaper Oekonomische Nachrichten der Patriotischen Gesellschaft in Schlesien, issued weekly in Wrocław in the years 1773–1781. The quality of the original sub-daily temperature data was assessed in accordance with WMO recommendations. In addition, mean daily and monthly values were compared and validated against time series from other sites located near Wrocław (Żagań, Jelenia Góra, Prague, Berlin and Warsaw). Air temperatures in Wrocław during the period 1773–1781 were 1.4 and 0.5 °C warmer than in the respective equivalent periods 100 and 200 years later (i.e., 1873–1881 and 1973–1981) but 1.9 °C colder than in the most recent period (2013–2021). The increase in temperature between the study period and the most recent period was greatest in summer (2.7 °C) and winter (2.4 °C) and smallest in autumn (0.8 °C).