A composite monthly temperature record from Tornedalen in northern Sweden, 1802–2002



Previously unexplored observational temperature data for the period 1802–62 from Övertorneå and Kalix in the Tornedalen area in subarctic Sweden (∼66 °N), have been analysed. These early data have been combined with the temperature series from the synoptic weather station in Haparanda, beginning in August 1859, to develop a continuous Tornedalen temperature series with monthly means 1802–2002. The temperature data between 1802 and 1859 have been adjusted to correspond to Haparanda temperatures using information from time periods with overlapping observations, both in the early period and in recently made observations at the original sites. Additional information for homogenizing the series was obtained from temperature series for Vardø, Oulu, and Helsinki. Our judgement is that the reconstructed Tornedalen temperature record is reliable back to November 1832. Before this, the summer (June–August) temperatures in particular are less reliable, whereas data for the other seasons seem to be realistic, at least on decadal time scales. The annual mean temperatures are judged as realistic back to the start of the record.

Between 1802 and 2000 there has been a warming trend in Tornedalen at an average rate of 0.099 °C decade−1 or 1.97 °C in total. The total warming explained by linear trends was greatest in winter (2.83 °C) followed by spring (2.17 °C), autumn (1.87 °C) and summer (0.88 °C). The annual warming trend during 1802–1900 was slightly greater than that for 1901–2000. Warming in winter contributed most to the rise in annual temperatures during the 19th century, whereas spring contributed most in the 20th century. The warmest decade was the 1930s, after which a strong cooling trend occurred until the 1970s (−0.325 °C decade−1, 1941–70). Warming then set in again to the end of the series (0.227 °C decade−1, 1971–2002). Copyright © 2003 Royal Meteorological Society