"The goal of this project is: • to develop a comprehensive description of the climatic and environmental changes in the Eastern Taimyr [72N-102E] for the warmest periods during the Holocene using tree ring width, latewood density, cell size, carbon and oxygen isotope data in wood and cellulose; • to improve our understanding of the physiological response of larch trees to environmental changes in the Eurasian north. We propose to investigate three periods, which are characterized by high temperatures during the Holocene: • the natural warm period BC 3700-3800, with an average temperature, which was three degrees higher than at present; • the Medieval Warm period AD 950-1150, with a similar rise in temperature compared to today; • the current period AD 1945-2006, which is characterized by the highest level of atmospheric carbon dioxide due to anthropogenic activities besides a temperature increase. The work will be conducted in three major fields: 1. Climatology – analyses of statistical relationships between climatic parameters (temperature, precipitation, relative humidity, and vapor pressure deficit) and carbon, oxygen isotope data during the current period. Comparison of isotope chronologies along the Subarctic latitudes from Yakutia to Sweden with Greenland ice core and pollen data. 2. Physiology - investigation of the physiological response of trees to environmental changes during the current and past periods based on a combined carbon and oxygen isotope fractionation model developed by Scheidegger et al. (2000). 3. Modeling – the new isotope and tree ring chronologies will be used to verify the ecophysiological model [Hemming et al. 2001; Vaganov et al. 2006] for the current period and to extend the model for the past to infer new environmental information (e.g. on water use efficiency)."