Climate Scenarios and Models Used For Developing the 2005 Pacific Northwest Climate Change Scenarios

Climate Scenarios

As part of the global effort to quantify future changes in climate, the Intergovernmental Panel on Climate Change (IPCC) has developed different scenarios of change in greenhouse gas and sulfate aerosol emissions for use in global climate modeling efforts. These scenarios are grouped in four categories, or storylines, based on different assumptions about demographic, social, economic, technological, and environmental change.

The CIG chose two scenario families for its most recent update of the Pacific Northwest climate change scenarios:

• A2 Scenario Family. The A2 scenario family lies near the upper limit of future greenhouse gas emissions as projected in different emissions scenarios, particularly beyond 2050. The A2 scenario assumes continuously increasing population growth, slower adoption of non-fossil fuel sources, and slower technological change than other scenarios.
• B1 Scenario Family. The B1 scenario family lies near the lower limit of projected changes in greenhouse gas emissions. The B1 scenario assumes global population growth peaks by mid-century and then declines, a rapid economic shift towards service and information economies, and the introduction of clean and resource-efficient technologies.

Both scenario families are considered equally probable. For more information on these and other scenario families, please see the IPCC's Special Report on Emissions Scenarios (2000).

Climate Models

The Climate Impacts Group has analyzed the climate response for the Pacific Northwest simulated by several climate models. These simulations were prepared by climate modeling centers worldwide for the Fourth IPCC Assessment (also referred to as AR4). For consistency with prior CIG work, we include the current versions of models used previously: HadCM3, ECHAM5, CCSM3, and PCM1 (CCSM3 is the successor to both the NCAR CSM and DOE PCM). To these we added five additional models to better represent the range of models participating in AR4. These are: CNRM_CM3, CSIRO_MK3 Miroc_3.2, IPSL_CM4, CGCM_3.1, and GISS_ER.