Reconstructions of climatic conditions in Greenland and Labrador/Nunatsiavut ca. 1770 to 1939 from Moravian Missionary Observations (MORCLIM)

This study presents a reconstruction of climatic conditions (air temperature and pressure, wind speed and direction) in coastal Greenland and Labrador/Nunatsiavut (Canada) for 1771–1939, with particular emphasis on thermal variability along the coasts of Greenland and Labrador/Nunatsiavut. The analysis is based on long-term instrumental meteorological observations systematically recorded by the Moravian Brethren, whose measurements provide rare and valuable early climate data from remote Arctic regions. Some of these observations were conducted on behalf of the Deutsche Seewarte. The historical records, preserved in major archival collections including the Moravian Archives in Herrnhut (Germany) and London (UK), and additionally sourced from the Deutscher Wetterdienst (Germany), constitute one of the longest continuous documentary sources of instrumental weather observations in the North Atlantic Arctic. Some of the data were also taken from other sources, e.g. old journals.

The Moravian missionary observations provide sub-daily instrumental measurements, typically recorded two to four times per day, forming one of the longest and most consistent early instrumental datasets available for the North Atlantic Arctic-subarctic region. By examining these records in a detailed and systematic manner, we aim to reconstruct regional thermal variability and long-term trends from the late eighteenth century through the early twentieth century.

All available historical data were quality-controlled and converted to present units (°C, hPa, ms ¹). The necessary corrections to all studied variables were introduced. For example, the original daily air temperature means (calculated from different measurement times) were corrected to real means calculated from 24-hourly measurements. Monthly corrections were calculated from hourly temperatures in the contemporary data (1991–2020). The corrected daily mean data have been used to calculate monthly, seasonal and yearly means and other statistics such as:  number of categories of cold/warm days, the growing degree-day sum (GDD), the air thawing index degree-day sum (ATI), the positive degree-day sum (PDD), and the air freezing index degree-day sum (AFI). Climate conditions during the study period in Greenland and Labrador were compared with present-day conditions (1991-2020). The results provide new insight into historical climate dynamics in the Arctic prior to the widespread establishment of modern meteorological networks. By extending the instrumental record back to the late eighteenth century, this research establishes an important historical baseline for assessing the magnitude and drivers of contemporary Arctic warming and contributes to a better understanding of long-term natural climate variability in coastal Greenland and Labrador/Nunatsiavut.

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