Artificial tree rings from climate simulations - Assessment of uncertainties of temperature reconstructions of the last millennium

• Applicant: Dr. Traute Crüger
• Subject Area: Atmospheric Science
• Term: from 2010 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 164010014

Zusammenfassung (deutsch)To assess anthropogenic climate change, the natural past climate and its variability have to be understood. Tree rings record environmental variation via their growth and are commonly used to reconstruct past temperatures prior to the instrumental period. Reconstructions of large-scale temperature show a remarkable spread. Current debate is centred around possible error sources in reconstructions. Reconstructions are based on the assumption that presently observed relationships between tree ring chronologies and temperatures are also valid in historical eras. This approach neglects potential multicausality and non-linearity between tree ring growth and environmental conditions. In addition, lowfrequency variability is difficult to preserve in dendrochronological reconstructions, due to relatively short observational calibration periods and the procedures to establish long tree ring chronologies. We aim to assess uncertainties and errors in temperature reconstructions. To consider biases inherent to tree-ring archives, we propose a novel approach: forward modelling of tree-ring variation. The project is based on simulations of the past 1200 years performed at the MPI for Meteorology with the MPI Earth- System Model including a vegetation module (ESM). These ESM data will be used to drive an ecophysiological forest model to derive artificial tree ring data. Applying state-of-the-art reconstruction techniques, the artificial tree ring data can be utilized to reconstruct large-scale temperatures of the climate simulations. The virtual world of ESM simulations and artificial tree ring data supplies an entire system knowledge allowing detailed investigations of reconstruction uncertainties and their sources, notably, the quantification of non-linearity and non-stationarity in the growth response to climate variation.

• DFG Programme: Research Grants
• Participating Person: Dr. Christian Reick