Expanding Pacific Marine Heatwave Threatens West Coast Climate and Ecosystems

A marine heatwave that peaked in September 2025 now covers a triangular zone from Hawaii to British Columbia and south to Mexico. NOAA’s May 2026 forecast expects further expansion and intensification.

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The heatwave overlaps a developing El Niño, a pairing that drove severe impacts during the 2015 “Blob.” Research links the combined events to the human-driven climate crisis, and models assign a > 2/3 chance of a strong or extreme El Niño later in 2026.

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Atmospheric scientist Kim Wood (University of Arizona), Berkeley Earth lead Robert Rohde, Oregon State climatologist Larry O’Neill, NOAA Fisheries researcher Elizabeth Phillips, and marine ecologist Hilary Hayford have spoken. NOAA and the federal drought status report provide official assessments.

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Eastern Pacific sea-surface temperatures now exceed typical peak-hurricane values. In March 2026, temperatures in Minnesota, Colorado and Idaho rose >30 °F above normal, reaching 88 °F (31 °C). Over one-third of U.S. stations set all-time March records. Federal data show the 2026 snowpack at low elevations in Oregon, California and Colorado melted completely, establishing a new benchmark low for Wyoming, Utah, Colorado and New Mexico.

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The heatwave intensifies land heat, fuels drought, and raises humidity that may trigger dry thunderstorms and wildfire. Marine shifts include great-white sharks off British Columbia, brown pelicans abandoning Mexican nests months early, and seabird migration linked to declining sardine and anchovy stocks. Krill, a key food source, has dropped similarly to the 2014-2016 Blob, threatening salmon and higher trophic levels.

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NOAA projects the heatwave will expand and strengthen, interacting with the anticipated El Niño, and will conduct an offshore ecosystem assessment June-September using the RV Reuben Lasker’s sonar to map krill, plankton and other base-level organisms. The federal drought status report warns the 2026 snowpack will set a new low benchmark, increasing water challenges.

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Researchers caution that even without further heatwave persistence, the region faces a severe wildfire season and strained water supplies. Hayford notes a lack of tools to address frequent, intense events, while O’Neill warns higher humidity may produce dry thunderstorms rather than beneficial rain.

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Sources agree on heatwave expansion, but quantitative forecasts of its duration and the magnitude of associated El Niño effects remain uncertain.

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• “I’m out of superlatives,” — Kim Wood, atmospheric scientist, University of Arizona

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• “would have been impossible without a boost from climate change” — Robert Rohde, lead scientist, Berkeley Earth

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• “incredibly long lasting” — Larry O’Neill, climatologist, Oregon State University

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• “The last six months have been really concerning,” — Elizabeth Phillips, research scientist, NOAA Fisheries

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The NOAA offshore ecosystem assessment begins in June 2026, with the RV Reuben Lasker conducting sonar surveys through September to track krill, salmon and the interaction of the heatwave with the projected strong El Niño.

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