Air temperature changes in SW Greenland in the second half of the 18th century

Abstract. The thermal conditions of south-western Greenland in the second half of the 18th century were estimated using two unique series of meteorological observations. The first series (Neu-Herrnhut, 1 September 1767 to 22 July 1768, hereinafter 1767–1768) is the oldest long-term series of instrumental measurements of air temperature available for Greenland. The second (Godthaab, September 1784 to June 1792) contains the most significant and reliable data for Greenland for the study period. The quality-controlled and corrected data were used to calculate daily, monthly, seasonal and yearly means. The daily means were further used to calculate day-to-day temperature variability (DDTV), thermal seasons, growing degree days (GDDs), the air thawing index (ATI), positive degree days (PDDs) and air freezing index (AFI) degree days. Air temperature in Godthaab (now Nuuk) was, on average, warmer than the present day (1991–2020) in 1767–1768 and colder in 1784–1792. Compared to the early 20th-century Arctic warming (ETCAW) period, the data for the two sub-periods show that the late 18th century was as warm or even warmer. Except winter 1767/1768, winters and springs in the study period were longer, while summers and autumns were shorter than at present. The analysed climate indices usually did not exceed the maximum and minimum values from 1991–2020. Mean daily air temperature in the studied historical periods rarely exceed ±2 SD (standard deviation) of the long-term mean calculated for the contemporary period. Air temperature distribution was usually close to normal, in both historical and contemporary periods.