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Emissions pathways, climate change, and impacts on California
Katharine Hayhoe1, Daniel Cayan, Christopher B Field
1ATMOS Research and Consulting, 809 West Colfax Avenue, South Bend, IN 46601, USA. hayhoe@atmosresearch.com
Summary
Future climate change impacts in California depend on emission pathways. Higher greenhouse gas emissions significantly increase extreme heat, reduce forests, and diminish snowpack, threatening water resources.
Area of Science:
- Climate Science
- Environmental Science
- Impact Assessment
Background:
- Future climate change magnitude is contingent on greenhouse gas emission pathways.
- The Intergovernmental Panel on Climate Change (IPCC) outlines various emissions scenarios.
Purpose of the Study:
- To explore climate change and impact implications in California under the highest (A1fi) and lowest (B1) IPCC emissions pathways.
- To assess the influence of different climate models on projected impacts.
Main Methods:
- Utilized climate projections from two state-of-the-art climate models: Parallel Climate Model (low sensitivity) and Hadley Centre Climate Model, version 3 (medium sensitivity).
- Analyzed implications across different emissions scenarios (B1 and A1fi).
Main Results:
- Annual temperatures nearly double from B1 to A1fi scenarios before 2100.
- Extreme heat and associated impacts are substantially greater under the A1fi scenario.
- By end-century under B1: heatwaves quadruple, heat mortality triples, alpine forests decrease 50-75%, Sierra snowpack reduces 30-70%.
Conclusions:
- Under A1fi scenario: heatwaves increase 6-8x, excess mortality 5-7x, alpine forests decrease 75-90%, snowpack declines 73-90%.
- Cascading impacts on water resources and potential disruption of California's water rights system are projected.
- Interscenario differences in impacts and adaptation costs emerge later in the century but depend on earlier emissions.