1. Climatic Research Unit; School of Environmental Sciences; University of East Anglia; Norwich; NR4 7TJ; UK
2. Department of Earth and Environment; Boston University; Boston; MA,; USA
3. Laboratory for Climate Sciences and the Environment (LSCE); Joint Unit of CEA-CNRS; Gif-sur-Yvette; France
4. Biospheric Sciences Branch, NASA Goddard Space Flight Center; Greenbelt; MD; 20771; USA