1. a Department of Environmental Science Policy and Management , University of California , Berkeley, CA, 94720-3312, USA
2. b Energy and Resources Group , University of California , Berkeley, CA, 94720-3050, USA
3. c National Geophysical Data Center , US National Oceanographic and Atmospheric Administration , 325 Broadway, Boulder, CO, 80303, USA
4. d Cooperative Institute for Research in Environmental Sciences , University of Colorado , Boulder, CO, 80303, USA