Climate Shift Index alert

Climate Central analysis shows that human-caused climate change made the record-breaking spring heat forecast in parts of the western U.S. and Canada up to 5 times more likely.

• Extended forecasts indicate record heat is likely over large areas of Washington, Oregon, California, Idaho and Montana in the U.S., and Alberta, British Columbia, and the Yukon Territory in Canada, from this Saturday, May 13, through Monday, May 15  2023. 

• Daily temperatures over this period are expected to reach Climate Shift Index levels of 2 to 5, indicating that human-caused climate change made this excessive heat two to five times more likely.

• By Sunday, May 14, temperatures could rise to levels not typically experienced until July and August. In parts of the Pacific Northwest, daytime temperatures are forecast to reach the upper 80s to mid 90s. Temperature records in the region for May 14 include  77°F (Vancouver, BC in 1997), 88°F (Seattle, WA in 2018), 89°F (Calgary, AB in 1924), and 95°F (Yakima, WA in 1973).

• These temperatures could present heat safety risks, particularly given the rapid increase in temperatures  following a cooler-than-average start to the week. Populations most vulnerable to high temperatures include older adults, young children, pregnant women, individuals with chronic conditions, members of low income and historically marginalized communities, athletes, and outdoor workers.

• For more information on heat and the related human health implications refer to our Climate Matters brief, More Risky Heat Days in 232 U.S. Locations, that found an increase in annual days above local risky heat thresholds throughout the Pacific Northwest. Seattle and Portland now experience 26 and 23 more risky heat days per year than in 1970, respectively.

This upcoming event is the latest in a string of unusual heat waves for this region, including a 2021 record-breaking heatwave that was made more than 1000 times more likely by human-caused climate change.

Quote from Dr. Andrew Pershing, director of climate science, Climate Central: "The Climate Shift Index reveals clear fingerprints of climate change on the high temperatures forecast for the Northwest. This heat represents a potentially serious human health risk for millions, and scientific analysis shows that these conditions would have been far less likely without the influence of carbon pollution."

Reporting resources as this heat event unfolds:

• Exposure to risky heat can trigger heat-related illnesses, including heat exhaustion and heat stroke, a life-threatening condition. For more information on heat safety, visit the National Integrated Heat Health Information System’s Planning and Preparing guide.

• The U.S. Climate Shift Index map tool has free maps showing the fingerprint of climate change on local average, maximum, and minimum temperatures. 

• The influence of climate change on daily average temperatures across the globe is available on the global Climate Shift Index map.

• Explore quick facts and local analyses on the links between climate change and extreme heat in Climate Central’s Extreme Weather Toolkit: Extreme Heat, World Weather Attribution’s guide to reporting on extreme heat and climate change, and a summary of the connection between heatwaves and climate change from Yale Climate Connections.

About the Climate Shift Index™

Climate Central’s Climate Shift Index™, grounded in the latest peer-reviewed science, maps the influence of climate change on temperatures across the globe, every day. 

Climate Shift Index™ levels indicate how much human-caused climate change has altered the frequency of daily temperatures at a particular location. Level 1 indicates that climate change is detectable in that day’s temperature. Level 2 means that climate change made exceptionally warm temperatures in a given location at least twice as likely. Level 5 is the maximum and indicates temperatures at least 5 times more likely because of climate change.

For this analysis, temperatures come from NOAA’s Global Forecast System model.