National and international reports on climate change, like the National Climate Assessment (NCA5) and Intergovernmental Panel on Climate Change’s 6th assessment report (IPCC AR6) provide broad information on climate change impacts for the nation and globe. Though useful, this information is often too broad to inform local-scale climate resilience efforts in Washington state. The IPCC AR6 includes regional climate impacts summaries for large regions of the United States, using global climate models that are coarse in their resolution. The NCA5 uses data that is more detailed, but does not include climate impact indicators that are relevant to Washington, like changes in snowpack and streamflow. Additional information is needed to understand the risks associated with specific greenhouse gas targets in Washington state.

Previous reports on climate impacts for Washington state have focused on assessing changes at future time periods (e.g., 2050s) and under specific future climate scenarios. In contrast, the recent IPCC AR6 and NCA5 reports included an assessment of climate impacts for specific global warming levels (GWLs). This perspective directly connects climate impacts with global warming targets, making it easier to assess climate risks associated with specific greenhouse gas emissions limits.

The Washington state legislature tasked the Washington state Department of Ecology, with support from the Climate Impacts Group, to analyze recent national and international climate reports and provide recommendations to Washington lawmakers on whether to amend Washington state’s statutory limits on greenhouse gas emissions (RCW 70A.45.040). As part of this effort, the Climate Impacts Group investigated future climate impacts in Washington state at multiple GWLs (1.5°, 2.0°, 3.0°, and 4.0°C). This work culminated in both a white paper that is included as an appendix to the Washington State Department of Ecology’s 2025 Summary Report on the Science of Human Caused Climate Change and Recommendations for Washington State’s Greenhouse Gas Emission Reduction Limits (Appendix C) and a fact sheet displaying some select results.

Read the report

View the fact sheet