According to the assessment report of the Intergovernmental Panel on Climate Change (IPCC) global warming is undoubtedly occurring. Moreover the dynamics of regional and seasonal climate changes will differ significantly. Model comparisons indicate that some parts of the globe and some seasons experience stable or in some cases even declining temperatures. In order to more comprehensively understand such particular regional and seasonal trends, palaeoclimatology directs its attention towards long-term climate reconstructions. Tree-ring based temperature reconstructions form the major part of the data base used for the IPCC report. Temperature reconstructions so far indicated a rise in temperatures during the last decades. One major criticism, however, is that the bulk of the tree-ring chronologies used were from trees growing near the latitudinal or altitudinal limits, e.g., Alpine regions and northern Scandinavia. This is especially true for all tree-ring chronologies longer than 500 years. In contrast, long-term reconstructions derived from trees growing well within their latitudinal or altitudinal limits are missing. Thus they are not part of the IPCC data base, which we believe is a crucial gap in the palaeoclimate database. For instance, no tree-ring-based temperature reconstructions of millennial scale are available as yet for the temperate lowlands in Europe! Preliminary studies, however, indicate that such reconstructions may reveal long-term trends that substantially differ from those obtained for the high latitudes and altitudes, thus leaving doubts concerning the representativeness of large hemispherical and global reconstructions concerning the temperate lowlands in Europe. This gap in the data base still exists until today because dendroclimatology at temperate lowland sites has been upset for three main reasons, i.e., diffuse climate-growth relationships, only short chronologies because long-living trees were rare and the potential loss of low-frequency signals due to short sample segment lengths. This dilemma can be solved by analysing tree-ring parameters, other than width, e.g., stable isotopes or cell structures, but measuring these parameters is very time-consuming. Recently, we have developed a new method applying confocal laser scanning microscopy which reduces the efforts for obtaining chronologies of cell-structure measurements. First analyses have shown that such chronologies contain strong climate signals indicating the great potential for climate reconstructions for the temperate lowlands in Europe. Therefore, the core objective of this project is to develop multi-centennial chronologies of cell-structure measurements for NE-Germany and N-Poland, which will be utilized for long-term reconstructions. Subsequent analyses will examine the climate dynamics and underlying modes, such as the North Atlantic Oscillation by means of climate simulations.

Partner:
Deutsches Archäologisches Institut, Referat Naturwissenschaften/Dendrochronologie, Berlin, Deutschland (Karl-Uwe Heußner)
Nicolaus Copernicus Universität, Institute for the Study, Restoration and Conservation of Cultural Heritage, Torun, Poland
University of Arizona, Laboratory of Tree-Ring Research, 1215 E Lowell St, Tucson, AZ 85721 USA (Tomasz Wazny)
Humboldt University Berlin, Geographisches Institut, Klimageographie, Berlin, Deutschland (Christoph Schneider)

Funding:
German Research Foundation (DFG),  259353585