The magnitude of future climate change depends substantially upon the greenhouse gas emission pathways we choose, as emissions during early decades establish the degree of climate change that will be experienced later in the century. Here we explore the implications of the highest and lowest IPCC emissions pathways for regional climate change and associated impacts in California. Based on HadCM3 and PCM climate projections, some differences in temperature projections and associated impacts emerge by mid-century. Greater differences are seen in the second half of the century, as increases in annual average temperature under the higher A1fi scenario are nearly double those under the lower B1 scenario. Substantial impacts for a number of temperature-sensitive sectors in California are projected to occur under both emissions scenarios, with more severe impacts occurring under A1fi towards the end of the century. More extreme and persistent summer heat could substantially increase the risk of heat-related mortality in both inland and coastal cities. Warmer winter and spring temperatures will likely reduce snowpack in the Sierra Nevada Mountains, with cascading impacts on winter recreation and summer water supply. Higher temperatures could also impact California’s leading agricultural products, reducing dairy production and diminishing the quality of growing conditions for wine grapes in all but the coolest grape-growing regions. A warmer and longer growing season and changes in moisture conditions is likely to alter the distribution of California’s natural vegetation types, with projected changes including a severe reduction the extent of alpine and subalpine forest and the widespread displacement of woodlands and shrublands by grassland. These findings support the conclusion that climate change and many of its impacts vary on a regional level scale with the quantity and timing of GHG emissions. As such, they represent a solid starting point for assessing the outcome of changes in GHG emission trajectories driven by climate-specific policies, and the extent to which lower emissions can reduce the likelihood and thus risks of “dangerous anthropogenic interference with the climate system”.