Das Projekt "Klima- und Umweltphysik" wird vom Umweltbundesamt gefördert und von Universität Bern, Physikalisches Institut, Abteilung für Klima- und Umweltphysik durchgeführt. In this proposal four streams 'Climate Modelling', 'Ice Core Analysis', 'Isotopes in the Environment' and 'Development of New Techniques' are presented with the motivation to contribute to the understanding of our global environment using a broad palette of physically based methods. The global ocean circulation and biogeochemical cycles will be simulated in dynamical models of the climate system. With these models we investigate the stability of the thermohaline circulation, natural variability and abrupt climate change and their effect on these cycles. This should contribute to a better understanding of the causes of glacial-interglacial CO2 variations and the atmospheric CO2 increase due to anthropogenic emissions. The GRIP ice core will be analysed and yield a high-resolution history of climate changes during the past 250000 years. Timeseries of various constituents in the ice core are being constructed and interpreted. Isotopic concentrations are measured in various environments in order to obtain a better understanding of processes such as the transfer of substances from the atmosphere into snow and ice of the transport of tracers in the ocean. Furthermore, isotopic ratios of oxygen and carbon in ice cores, tree rings and sea sediments are additional means to reconstruct past climatic conditions and determine time scales of climate variability. We work on a new method of measuring rare radionuclides in the environment. Leading Questions: What is the role of the deep ocean circulation during rapid climate change and during transitions from a glacial to an interglacial? What is the detailed sequence of climatic changes in different locations during the last 100'000 years? Are global climate changes always triggered in the Northern Hemisphere or is also the opposite sequence possible and what is the coupling between the two hemispheres? How did the different carbon reservoirs evolve during the last few hundred years and how are they influenced by future perturbations, and what is the effect of rapid and anthropogenic climate change on the carbon cycle? How can the measurements of different stable and radioactive isotopes be best combined to yield information about the hydrological cycle and the processes in groundwater systems?