Thermal conditions on the coast of Labrador during the late 18th century

Abstract. In this article, we present research results on the air temperature changes on the Labrador coast at the end of the 18th century (1771–87). This important climatic variable was studied on the basis of valuable instrumental meteorological observations made by Moravian missionaries. The data were taken from meteorological registers available in three major archives: the Moravian Archives in Herrnhut (Germany) and the Moravian Archives at Muswell Hill and the Archives of the Royal Society, both located in London (United Kingdom). The series of meteorological observations we used in the paper are the oldest and longest long-term meteorological observations available not only for Labrador, but for anywhere in the entire Arctic. Moravian missionaries measured not only air temperature (analysed here) but also atmospheric pressure and wind (force and directions) two, three or even four times a day. These unique data allow us to better understand the climate variability and trends in the region during the study's historical period. We have analysed sub-daily air temperature readings from three sites: Okak (1776–87), Nain (1771–86) and Hopedale (1782–86). The data were converted into more relatable present-day units and have undergone rigorous quality control. Original mean daily air temperature data calculated using different numbers of measurements per day were corrected to the “real” mean daily values. The corrected values were subsequently used for statistical analysis. The historical temperatures documented during our specified study period along the Labrador coast were compared with those experienced today. The analysis shows a significant warming from historical to present times. Historical data from Nain, Okak, and Hopedale, representing different periods were, on average, about 0.5 to 2.3 °C colder than in the modern period of 1990 to 2020, especially in winter and autumn. Most monthly mean air temperatures in historical times lie within two standard deviations of the modern mean. The frequency of temperature occurrence in one-day intervals suggests a shift towards more stable and less extreme temperature distributions in contemporary times, implying substantial changes in climate patterns over time in this region. The continentality of the Labrador climate, as well as year-to-year variability of mean monthly temperatures, were greater in historical times than at present.