A 'record-shattering' marine heatwave has pushed ocean temperatures at nearly every location to records for this time of year, and scientists are concerned about coastal flooding as the heatwave is expected to persist.
The stretch of coast from Sonoma County south to Ensenada, Mexico, is 10 degrees warmer than average. During a webinar Thursday, Swain described the event as 'mind-boggling' and 'record-shattering,' adding, 'I'm using all the superlatives in the book because I think they're appropriate.'
The water temperatures at nearly every location are higher than any recorded during the cold season, and are warmer than any point after November 1 and before May in any previous year, Swain said.
Warmer oceans cause water to expand, leading to high tides like those Long Beach and Orange County have experienced in recent months. Scientists are particularly focused on king tides expected around Thanksgiving, Christmas, and late January. Any significant rainstorms, which El Niño could bring, would worsen the flooding.
Swain explained that marine heatwaves take longer to develop and are more persistent because water takes longer to heat or cool than air, and wind can generally move air faster than ocean currents. 'Marine heat waves take a lot longer to develop, and they're a lot more persistent,' he said.
Analysis
Why This Matters
- The persistent warmth could lead to repeated coastal flooding during king tides, threatening homes, businesses, and infrastructure along the California coast.
- El Niño conditions may bring heavy rain on top of already high water levels, amplifying flood risks.
- The event is a stark example of how climate change interacts with natural variability to produce extreme conditions.
Background
Marine heatwaves are periods of unusually warm ocean temperatures that can last weeks to months. They have become more frequent and intense globally in recent decades, driven by climate change. California's current event is occurring during an El Niño, which itself tends to warm the eastern Pacific.
Key Perspectives
Daniel Swain, UC climate scientist: called the marine heatwave 'mind-boggling' and 'record-shattering,' noting that water temperatures are warmer than any recorded for the period after November 1 and before May. He warned that the event is likely to be persistent because marine heatwaves develop and dissipate more slowly than atmospheric ones.
What to Watch
- Thanksgiving week king tides: the first major test of how the warm water interacts with high tides.
- Any El Niño-driven rainstorms that could combine with elevated sea levels to cause urban flooding.
- Whether the heatwave persists into late January, when the next king tide cycle arrives.
Checked
11 claims in this story checked against 1 source: 9 supported.
Show each claim
- SupportedThe record-shattering marine heat wave means California’s coastal flood threat will stick around.LAist: “California’s 'record-shattering' marine heat wave means threat of coastal flooding will stick around.”
- Partly supportedOcean temperatures along the coast are 10 degrees warmer than average.LAist: “The ocean temperatures along a stretch of coast from Sonoma County down to Ensenada, Mexico, are 10 degrees warmer than average.”
- SupportedScientists are watching for king tides around Thanksgiving, with more expected around Christmas and late January.LAist: “Scientists are especially watching for king tides during Thanksgiving week . (King tides are also expected around Christmas and in late January.)”
- Partly supportedThe marine heat wave pushed ocean temperatures at nearly every location to records for this time of year.LAist: “The water temperatures in nearly every location are higher than any measured during the cold season in recorded history.”
- SupportedScientists are concerned about coastal flooding as the heat wave is expected to persist.LAist: “El Niño is making the California coast much warmer than usual, and scientists are concerned about coastal flooding.”
- SupportedThe stretch from Sonoma County south to Ensenada, Mexico, is 10 degrees warmer than average.LAist: “The ocean temperatures along a stretch of coast from Sonoma County down to Ensenada, Mexico, are 10 degrees warmer than average.”
- SupportedDuring a Thursday webinar, Swain called the heat wave “mind-boggling” and “record-shattering” and said, “I'm using all the superlatives in the book because I think they're appropriate.”LAist: “In a webinar Thursday, University of California climate scientist Daniel Swain stressed how unusual the current heat wave is, describing it as “mind-boggling” and “record-shattering.” “I'm using all the superlatives in the book because I think they're appropriate,” Swain said.”
- SupportedTemperatures in nearly every location are higher than any measured during the cold season in recorded history and warmer than at any point after November 1 and before May in any previous year, Swain said.LAist: “The water temperatures in nearly every location are higher than any measured during the cold season in recorded history. “Not only is the water warmer than it's ever been at this time of year, but in fact it is warmer than it has ever been at any point after Nov. 1 and before May in any previous year,” Swain said.”
- SupportedWarmer oceans expand, leading to high tides like those Long Beach and Orange County have experienced in recent months.LAist: “Warmer oceans mean that the water expands, leading to high tides like the ones Long Beach and Orange County have experienced in recent months.”
- SupportedSignificant rainstorms, which El Niño could bring, would make flooding worse.LAist: “And any significant rainstorms — which El Niño could bring — would also make flooding worse.”
- SupportedSwain said marine heat waves take longer to develop and are more persistent because water heats or cools more slowly than air and wind generally moves air faster than ocean currents.LAist: ““ Marine heat waves take a lot longer to develop, and they're a lot more persistent,” Swain said. That’s because water takes longer to heat up or cool down than air, and because wind can generally move air faster than ocean currents.”
