Why an immense marine heatwave off the US west coast has alarmed scientists

An unprecedented marine heatwave off the US west coast has scientists deeply concerned as new data reveals its ecological and environmental impacts are worsening. The warm water mass, which peaked in September 2025, now stretches thousands of miles from California to Hawaii, British Columbia, and Mexico, covering a vast oceanic region. Recent NOAA projections indicate the heatwave will expand and intensify in the coming months, coinciding with the development of El Niño in the tropical Pacific. The heatwave’s persistence has already triggered extreme land-based temperatures, with March 2026 seeing record-breaking warmth across the US. Abnormally warm Pacific waters retain and re-release atmospheric heat, altering weather patterns and contributing to unprecedented conditions. In March, temperatures soared over 30°F above seasonal norms in regions like Minnesota, Colorado, and Idaho, with hundreds of US weather stations—from San Francisco to New York—setting new all-time March records. Robert Rohde, lead scientist at Berkeley Earth, noted the heatwave would have been impossible without climate change’s influence. Some areas, including Phoenix, recorded temperatures higher than any previous April readings, a rare occurrence in modern records. Rohde compared the event to the Dust Bowl era, when record-setting was more common due to limited monitoring. Climate scientists are revisiting their assumptions about ocean-atmosphere interactions, as ocean temperatures in the eastern Pacific have surged to levels typically seen during peak hurricane season. Kim Wood, a University of Arizona atmospheric scientist, expressed shock at the data, emphasizing the heatwave’s role in accelerating climate crisis effects. The event follows the warmest winter on record in the western US, signaling deeper environmental shifts ahead.