Climate conditions in SW Greenland in the second half of the 18th century

To determine the climate conditions of SW Greenland in the second half of the 18th century, two series of meteorological observations have been used. The first series (Neu-Herrnhut, 1st Sep 1767−22nd Jul 1768) is the oldest long-term series of instrumental measurements of air temperature and atmospheric pressure made by Christopher Brasen (1738−1774). The second (Godthab, Sep 1784−Jun 1792) contains the most significant and reliable data for Greenland for the study period. Observations were made by Danish Reverend Andreas Ginges (1754–1812) using methodology and instruments provided by the Meteorological Society of the Palatinate. Sub-daily or daily data exist for the following periods: Sep 1784−Jun 1785, Jan−Jun 1787, Nov−Dec 1788, Jan 1790−Jun 1792 and are available in the manuscript entitled Astronomiske og meteorologisk Iagttagelser, anstillede i Godthaab i Grønland 1782–1792 and in the society’s yearbook Ephemerides Societatis Meteorologicae Palatinae, which contains data for 1787. All available historical data were quality controlled and corrected prior to being used to calculate daily (MDAT), monthly, seasonal and yearly means. Daily means have been used to calculate less typical climate statistics such as day-to-day temperature variability, thermal seasons, growing degree days (GDD), air thawing index (ATI), positive degree-days (PDD) and air freezing index degree-days (AFI).             Compared to present day (1991–2020), air temperature in Godthab was, on average, warmer in 1767–68 and colder in 1784–92. In 1767–68, the turn of December to January was exceptionally warm, with positive MDAT reaching even 5 °C. So too was summer significantly warmer than today. On the other hand, in 1784–92, autumn and particularly winter were markedly colder than today, while temperatures in the rest of the year were comparable to present day. The GDD and ATI in each month in the expedition year 1767–68 were equal to or higher than the norm observed in 1991–2020. No important changes were observed for PDD, while AFI was usually lower than the present-day norm. The GDD and ATI in the period 1784–92 usually (except 1787) do not exceed the maximum and minimum values from 1991–2020. The PDD during the cold season (from October to April) in the period 1784–92 is close to the average and minimum PDD in 1991–2020, but the AFI values in 1784–92 are between the average and maximum AFI values calculated for 1991–2020. The work was supported by the National Science Centre, Poland project No. 2020/39/B/ST10/00653.