1. Wegener Center for Climate and Global Change and IGAM/Institute of Physics; University of Graz; Graz Austria
2. Austrian Polar Research Institute; Vienna Austria
3. Lamont-Doherty Earth Observatory; Columbia University; Palisades New York USA
4. Department of Applied Physics and Applied Mathematics; Columbia University; New York New York USA
5. Department of Earth and Environmental Sciences; Columbia University; New York New York USA
6. Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA