Lead


Lay summary
Current climate change research is fundamentally challenged by three questions: (i) the characteristics of natural climate variability, (ii) the discrimination of anthropogenic forcing, and (iii) ecological, societal and economic risks when natural variability and anthropogenic forcing are superposed in a future climate. Insight into the regional (here Alpine) expression of climate change and changes of variability is critically important for two reasons: (1) regional trends (e.g. in the Alps), amplitudes and statistics of extremes strongly exceed values reported for the global scale, and (2) latest modelling results (IPCC AR4) suggest that Europe is globally the hotspot for a future increase in the inter-annual variability (e.g., summer temperatures), which will be the greatest challenge.
This project will examine varved (annually laminated) lake sediments and provide seasonally to annually resolved quantitative time series for temperature and precipitation for the eastern and north-western Swiss Alps (Engadine, Berner Oberland) back to ca 3300 years. Varved lake sediments are unique paleoclimatic archives and most suitable for very long records since they preserve the low-frequency (>10^2 yrs) climate signal.
More specifically, this project will extend the record of interannual quantitative autum SON temperature reconstructions (biogenic silica flux, r=0.70), summer precipitation reconstructions (mica/chlorite ratios, r=0.59) and autum precipitation (mica/plagioclase ratios, r=0.68) in Lake Silvaplana back from 1580 AD to 1300 BC. The applicability of the methods will be tested for Lake Seeberg and Lake Oeschinen in the limestone province and the climate regime of the northwester Swiss Alps. These time series will provide insight into (i) the structure and absolute amplitudes of decadal-century scale climate variability, (ii) quantified multi-decadal climate trends and rates of change, (iii) the hypothesis of greater interannual climate variability during warm periods of the past (e.g. Iron/Roman Age, Medieval ), as it is suggested for Central Europe in the future (“global hotspot of variability”).
This project develops in the core theme of IGBP and WCRP PAGES / CLIVAR Intersection. Our data are made available to the NOAA WDC data base for Paleoclimatology.