Thermal conditions in Nain (Labrador) from the late 18th century to the Second World War based on Moravian missionaries’ observations

This study examines the long-term thermal conditions in Nain, located on the coast of Labrador, and their changes by utilising all available sub-daily meteorological observations from the Arctic. Systematic weather recording began in 1771, when Moravian missionaries established a station among Inuit communities in the region now known as Nunatsiavut. They conducted measurements until 1939, although these were likely not continuous throughout the entire period. The long-term series of sub-daily air temperatures is available for the following intervals: 1771–1786, 1882–1913, and 1926–1938. For comparison, we also include a recent period of temperature data from 1990 to 2020. Thus, the analysis focuses on four periods representing important climatic phases: the Late Little Ice Age (LIA, 1771–1786), the Transitional Period (TP, 1882–1913) from the LIA to the Early Twentieth-Century Warming (ETCW), the mature phase of the ETCW (1926–1938), and the Contemporary Warming (CP, 1990–2020).
All sub-daily temperature data (recorded two to four times per day during the first period and at higher frequencies in later periods) were digitised, converted to modern Celsius units, and subjected to quality control. Mean daily air temperatures (MDATs) were calculated from the prepared sub-daily readings using a simple arithmetic mean. Next, MDATs were corrected to the so-called real daily mean using adjustment functions derived from contemporary hourly observations (1991–2010). These corrected MDAT values were then used to compute monthly, seasonal, and annual averages, as well as day-to-day temperature variability and thermal indices, including growing degree days (GDD), positive degree days (PDD), the air thawing index (ATI), and freezing degree days (FDI). 
Preliminary analysis shows that the first two periods were the coldest, particularly the TP, with a mean annual temperature of -4.9°C. The winter temperature averaged -19.3 °C, while the summer temperature averaged 7.2 °C. In contrast, warming began with the onset of the ETCW, although it was clearly weaker than during the CP. In the most recent period, the mean annual, winter, and summer temperatures were -2.3°C, -15.4°C, and 9.3°C, respectively. From the late 18th century to the present, air temperature in Nain has increased by approximately 4 °C in winter and 2 °C in summer, while the annual temperature has risen by 2.6 °C. Other analysed characteristics (e.g., the frequency of MDATs in 1-degree intervals) show a significant decrease in cold events and an increase in warm events after the ETCW period.

The work was supported by the National Science Centre, Poland, project No. 2020/39/B/ST10/00653.