Recent air and ground temperature increases at Tarfala Research Station, Sweden

• Main Authors: Ulf Jonsell, Regine Hock, Martial Duguay
• Format: Article
• Language: English
• Published: Norwegian Polar Institute 2013-07-01
• Series: Polar Research
• Subjects: Air temperature; climate change; permafrost; lapse rate; degree-days; NAO
• Online Access: http://www.polarresearch.net/index.php/polar/article/download/19807/pdf_1

Long-term data records are essential to detect and understand environmental change, in particular in generally data-sparse high-latitude and high-altitude regions. Here, we analyse a 47-year air temperature record (1965–2011) at Tarfala Research Station (67° 54.7′N, 18° 36.7′E, 1135 m a.s.l.) in northern Sweden, and a nearby 11-year record of 100-m-deep ground temperature (2001–11; 1540 m a.s.l.). The air temperature record shows a mean annual air temperature of −3.5±0.9°C (±1 standard deviation σ) and a linear warming trend of ±0.042°C yr−1. The warming trend shows large month-to-month variations with the largest trend in January followed by October. Also, the number of days with positive mean daily temperatures and positive degree-day sums has increased during the last two decades compared to the previous period. Temperature lapse rates derived from the mean daily Tarfala record and an air temperature record at the borehole site average 4.5°C km−1 and tend to be higher in summer than in winter. Mean summer air temperatures at Tarfala explain 76% of the variance of the summer glacier mass balance of nearby Storglaciären. Consistent with the observed increase in Tarfala's air temperature, the ground temperature record shows significant permafrost warming with the largest trend (0.047°C yr−1) found at 20 m depth.