The Pacific Ocean off the California coast was experiencing record-high temperatures well before the National Oceanic and Atmospheric Administration declared the onset of El Niño this month. The El Niño, now stirring offshore, will collide with the marine heat wave to create a rare convergence of warming conditions—the most powerful in decades, and one whose consequences are already unfolding.
A group that monitors waters off Marin County, Point Blue Conservation Science, recorded a 2°C to 3°C increase in average surface temperatures during the winter and early spring. Jaime Jahncke, the director of the nonprofit’s California Current Group, said such a rise is comparable to those seen in the 1997-1998 El Niño and the 2014-2015 marine heat wave, which scientists dubbed “the blob.”
The warming is already affecting coastal areas in Marin, San Francisco, and Santa Cruz Counties, where residents are seeing shifts in commercial fishing seasons.
“Each of these warm water events happens a little bit differently,” Pete Warzybok, the principal scientist and Farallon program leader at Point Blue, told the Light. “We tend to lump them all together, but each event is somewhat different, and that can impact what effect it has on marine life.”
Historically, these warm periods had lasting repercussions, depleting nutrients in the surface waters that coastal species and marine life depend on. Warm surface waters increase stratification and limit vertical mixing with colder water, creating less favorable conditions for phytoplankton growth.
What can start as a decrease in krill or range shifts of intertidal species can snowball, eventually affecting seabird mortality, large fish migrations, whales, humans, and coastal economies.
So far, West Marin has not seen dramatic effects from the marine heat wave due to a phenomenon especially productive in Northern California: seasonal upwelling.
Upwelling is a process in which strong winds push surface waters out, allowing for colder, nutrient-rich deep water to rise and replace them. The effect can be dramatic: In May, Point Blue observed a 3.2°C drop in water temperatures in just a couple of days. That month, northerly winds gusted up to 23 miles per hour—slightly higher than those measured in May 2025.
Mr. Warzybok said the early heat wave delayed the breeding activities of several seabirds, including common murres and Brandt’s cormorants, and pinnipeds around the Farallon Islands by roughly three or four weeks. But strong northerly winds led the waters to quickly turn murky with plankton blooms—a telltale sign of increased productivity.
Still, Mr. Warzybok said, coastal species are not yet in the clear. “We don’t yet know how this developing El Niño will interact with the ongoing marine heat wave,” he said. “We have relatively few examples of these events occurring simultaneously, so there remains considerable uncertainty about how marine wildlife and coastal ecosystems will respond in the coming months.”
When NOAA announced the development of El Niño on June 11, it cited a 63 percent chance that surface temperatures would exceed a threshold that would make the event notably strong.
El Niño conditions typically develop through summer, peak in winter, and interfere with the wind patterns that drive upwelling. Specifically, the eastward shift of warming water will gradually weaken the atmospheric pressure systems that drive northerly winds in the Pacific. For Northern California in particular, this could make for a warmer winter.
NOAA meteorologist Dylan Flynn said the success of upwelling and the persistence of northern winds throughout the summer will heavily influence the outcome of El Niño in West Marin.
The pattern’s effect on local ecosystems will depend on when it hits the coast. If upwelling subsides too early and surface waters are allowed to warm, food will become sparse for last spring’s seabird hatchlings.
In recent years, sea surface warming has been linked to widespread seabird “wrecks”: unusually high numbers of seabirds washing up on the California coast due to starvation. During the 2015 marine heat wave, 62,000 seabirds washed up across California beaches.
Point Blue, alongside the Greater Farallones National Marine Sanctuary beach watch program, will monitor the number of dead seabirds that wash up on beaches.
Other impacts are already visible.
Earlier this year, the California Department of Fish and Wildlife adjusted regulations for the commercial Dungeness crab fishery in Northern California in response to ongoing shifts in humpback whale migration patterns and increased risk of entanglement in fishing gear.
Warm waters have also compelled many other species, including tuna and salmon, to alter their migration schedules, prompting fisheries to adjust; this phenomenon is described by Michael Jacox, a research oceanographer at NOAA, as thermal displacement.
Dr. Jacox said that thermal displacement may be exacerbated around peninsulas such as Point Reyes in the years to come. In bays and lagoons, the source water available for upwelling is often relatively shallow, containing fewer nutrients than the colder, deeper waters that typically fuel coastal productivity.
These near-term disruptions, researchers say, are part of a longer-term shift in coastal productivity.
Looking decades into the future, model projections remain divided on how climate change will affect the strength of upwelling along the Northern California coast.
“The models in the Point Reyes area don’t agree on whether upwellings will become stronger or weaker,” Dr. Jacox said. “But what they do actually agree on is that the water will contain fewer nutrients.”
At the same time, advances in ocean monitoring and forecasting have improved scientists’ ability to anticipate marine heat waves, whale migration patterns, and changing ocean conditions. Better forecasting, Dr. Jacox said, could help managers adjust fishing practices before species move into areas where they are most vulnerable—minimizing avoidable impacts on marine life.