We study high-resolution climate variability through the analysis of tree-rings and other palaeoclimate archives at regional to global scales. Instrumental climate data are evaluated and used for the calibration of these archives to reconstruct climate over the past couple hundred to thousand years. We teach introductory and methodological courses on climatology with emphasis on spatial patterns and long-term changes of climate and ecological variability.

Trees are an excellent archive as they record environmental changes and impacts in a high temporal resolution by forming an annual distinct ring each year. Dendrochronology, or tree-ring analysis, is applicable to a variety of climatological and ecological research questions, including, inter alia, climate reconstructions, growth responses to extreme climatic events, and insect outbreaks. In this new study we expand the disciplinary boundaries of tree-ring research and introduce warfare dendrochronology.
We used annual growth rings of pine and birch trees as witnesses of the deployment of the German battleship Tirpitz at the Kåfjord in northern Norway. The Tirpitz was the target of several Allied air attacks, but the Kriegsmarine (German navy from 1935 to 1945) used artificial smoke, consisting of chlorosulfonic acid and zinc/hexachloroethane, to hide the ship. These smoke-screen actions throughout 1944 caused pine forests surrounding the Kåfjord to exhibit a strong and unusual growth decline during the following year. The tree damage extended up to 4 km away from the Tirpitz and in the most extreme case, growth was interrupted for nine years.