Working Paper Series

Emissions pathways, climate change, and impacts on California


  • Michael W. Hanemann, Goldman School of Public Policy, University of California, Berkeley
  • Katharine Hayhoea, ATMOS Research and Consulting
  • Daniel Cayan, The Scripps Institution of Oceanography
  • Christopher B. Field, Carnegie Institution of Washington
  • Peter C. Frumhoff, Union of Concerned Scientists, Two Brattle Square
  • Edwin P. Maurer, Santa Clara University
  • Norman L. Miller, Lawrence Berkeley National Laboratory
  • Susanne C. Moser, National Center for Atmospheric Research
  • Stephen H. Schneider, Stanford University
  • Kimberly Nicholas Cahill, Carnegie Institution of Washington
  • Elsa E. Cleland, Carnegie Institution of Washington
  • Larry Dale, Lawrence Berkeley National Laboratory
  • Ray Drapek, U.S. Department of Agriculture Forest Service
  • Laurence S. Kalkstein, University of Delaware
  • James Lenihan, U.S. Department of Agriculture Forest Service
  • Claire K. Lunch, Carnegie Institution of Washington
  • Ronald P. Neilson, U.S. Department of Agriculture Forest Service
  • Scott C. Sheridan, Kent State University
  • Julia H. Verville, Union of Concerned Scientists, Two Brattle Square


  • Goldman School of Public Policy Working Paper (June 2004)


The magnitude of future climate change depends substantially on
the greenhouse gas emission pathways we choose. Here we
explore the implications of the highest and lowest Intergovernmental Panel on Climate Change emissions pathways for climate
change and associated impacts in California. Based on climate
projections from two state-of-the-art climate models with low and
medium sensitivity (Parallel Climate Model and Hadley Centre
Climate Model, version 3, respectively), we find that annual temperature increases nearly double from the lower B1 to the higher
A1fi emissions scenario before 2100. Three of four simulations also
show greater increases in summer temperatures as compared with
winter. Extreme heat and the associated impacts on a range of
temperature-sensitive sectors are substantially greater under the
higher emissions scenario, with some interscenario differences
apparent before midcentury. By the end of the century under the
B1 scenario, heatwaves and extreme heat in Los Angeles quadruple
in frequency while heat-related mortality increases two to three
times; alpinesubalpine forests are reduced by 50–75%; and Sierra
snowpack is reduced 30–70%. Under A1fi, heatwaves in Los
Angeles are six to eight times more frequent, with heat-related
excess mortality increasing five to seven times; alpinesubalpine
forests are reduced by 75–90%; and snowpack declines 73–90%,
with cascading impacts on runoff and streamflow that, combined
with projected modest declines in winter precipitation, could
fundamentally disrupt California’s water rights system. Although
interscenario differences in climate impacts and costs of adaptation
emerge mainly in the second half of the century, they a

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