Overview of the California climate change scenarios project

In response to an Executive Order by California Governor Schwarzenegger, an evaluation of the implications to California of possible climate changes was undertaken using a scenario-based approach. The “Scenarios Project” investigated projected impacts of climate change on six sectors in the California region. The investigation considered the early, middle and later portions of the twenty-first century, guided by a set of IPCC Fourth Assessment global climate model runs forced by higher and lower greenhouse gas emission scenarios. Each of these climate simulations produce substantial impacts in California that would require adaptations from present practices or status. The most severe impacts could be avoided, however, if emissions can be held near the lower end of global greenhouse gas emissions scenarios. It is increasingly apparent that the rising atmospheric concentration of greenhouse gases (GHGs), resulting from human activities, is changing the climate in ways that pose serious risks to California’s health, economy, and environment. Furthermore, the more GHGs accumulate in the Earth’s atmosphere, the more the climate is likely to change and the greater the risks that Earth’s system processes and society will face (IPCC 2007). If actions are not taken soon, substantial impacts are likely to happen sooner and grow to larger magnitudes. Climatic Change (2008) 87 (Suppl 1):S1–S6 DOI 10.1007/s10584-007-9352-2 D. R. Cayan (*) Climate Research Division, Scripps Institution of Oceanography, UCSD, U.S. Geological Survey, 201 Nierenberg Hall, La Jolla, CA 92093-0224, USA e-mail: [email protected] A. L. Luers Union of Concerned Scientists, Berkeley, CA, USA G. Franco California Energy Commission, Sacramento, CA, USA M. Hanemann University of California, Berkeley, Berkeley, CA, USA B. Croes California Air Resources Board, Sacramento, CA, USA E. Vine California Institute for Energy and Environment, Sacramento, CA, USA Recently a number of U.S. local and regional efforts have begun to join the international community to address the increasing risks of climate change and have set policies to reduce GHG emissions. Amongst these actions, California has begun to consider the need to manage climate change through a combination of mitigation and adaptation strategies. California has been a leader in both supporting research on the science of climate change as well as in identifying solutions for reducing GHG emissions. In 2002, the California Legislature passed the first law to regulate GHG emissions from passenger vehicles. In the following year, the state established the California Climate Change Center, which is one of the first and perhaps the only state-sponsored research institution in the nation dedicated to regional climate change research. On June 1, 2005, Governor Arnold Schwarzenegger signed Executive Order S-3-05, which called for specific emission reductions and a periodic update on the state of climate change science and the emerging understanding of potential impacts on climate-sensitive sectors including the state’s water supply, public health, agriculture, coastal areas, and forestry. In response to this Executive Order, the California Energy Commission (Energy Commission) and the California Environmental Protection Agency (Cal/EPA) commissioned an assessment of the potential impacts of climate change on key state resources (“the Scenarios Project”). This special issue presents the results of the Scenarios Project. The Scenarios Project was conceived in early summer 2005 out of discussions among State administrators and scientists from various California Universities, federal and state agencies, and non-governmental organizations. The project was directed by a team of state government staff and non-governmental scientists, including those from the California Climate Change Center (the “Center”), an effort engaged to study long-term climate issues in California. The political, scientific and organizational landscape that led up to this effort is described in this volume by Franco et al. The Scenarios Project builds upon previous efforts to assess potential climate change impacts in California (e.g., Field et al. 1999; Barnett et al. 2004; Hayhoe et al. 2004). Explicitly, it extends the work of Hayhoe et al. 2004, which compared the projected impact of climate change in California under differing emissions scenarios. The Scenarios Project drew upon experts within and outside of the Center to produce a collection of reports on the projected impacts of climate change under multiple scenarios across six different sectors: coasts, water resources, agriculture, public health, forestry, and electricity production and demand. These reports are posted electronically on a State of California web page: http://www.climatechange.ca.gov/ climate_action_team/reports/index.html. The articles in this special issue are based upon these reports. The climate projections for the Scenarios Project are from three global climate models (PCM, GFDL, HadCM3) for three greenhouse gas emissions scenarios – a lower emissions (SRES B1), a medium-high emissions (SRES A2), and a higher emissions scenario (SRES A1fi). As described by Cayan et al. (in this issue), these projections contain increases in temperature that range from about +2°C to about +6°C by the end of the century, but contain relatively little change in precipitation. Statistical techniques were used to downscale these climate projections to incorporate in sector-specific assessments. These global climate models and emission scenarios bracket the potential climate outcomes expected from the full range of models and scenarios available from the IPCC. And as noted by Bonfils et al. (in this issue), the observed regional warming over the twentieth century during winters and springs in California lies on the outside edge of trends that could be attributed to estimated natural variability, and, therefore, the findings suggest that the warming over the twentieth century is associated with human-induced changes. Sea level rise due to climate change is a priority concern for California which has one of the longest coasts in North America. Cayan et al. (in this issue) show that projected sea S2 Climatic Change (2008) 87 (Suppl 1):S1–S6