They call it “the Blob.”

A decade ago, sea surface temperatures in the Pacific shot up to 11 degrees Fahrenheit hotter than normal. A high pressure system parked over the ocean, and winds that churn cold, nutrient-rich water from the depths to the surface died down. Stagnant, warm water spread across the Northeast Pacific, in a marine heat wave that lasted for three years.

Under the surface, the food web broke down and ecosystems convulsed, at first unseen to humans on shore. But soon, clues washed up.

Dead Cassin’s auklets — small, dark gray seabirds — piled up on West Coast beaches. The auklets were followed by common murres, a slightly bigger black-and-white seabird. The carcasses were knee-deep in places, impossible to miss.

Researchers are still untangling the threads of what happened, and they caution against drawing universal conclusions from a single regional event. But the Blob fundamentally changed many scientists’ understanding of what climate change could do to life in the ocean; 10 years later, the disaster is one of our richest sources of information on what happens to marine life as the temperature rises.

And it is more relevant than ever. Last year, multiple “super-marine heat waves” blanketed parts of the ocean. Averaged together, global sea surface temperatures broke records, often by wide margins, for months in 2023 and 2024. As the climate warms, scientists expect extreme marine heat waves to become more frequent.

The Blob “was a window into what we might see in the future,” said Julia Parrish, a marine ecologist at the University of Washington who runs the Coastal Observation and Seabird Survey Team, a network of volunteers who survey beaches from Northern California to Alaska.

In a study published last year, Dr. Parrish and her colleagues estimate that the Blob eventually killed millions of seabirds, in waves of starvation.

More recently, researchers undertook a thorough post-mortem of the Blob in the Greater Farallones National Marine Sanctuary, off the California coast.

The sanctuary is one of 17 pockets of U.S. waters protected to varying degrees from development and industry. They are becoming test beds for ways people can try and help marine life — and the human livelihoods that depend on the ocean — adapt to climate change.

This summer, the National Oceanic and Atmospheric Administration published a “condition report” for the Greater Farallones, along with an accompanying climate vulnerability assessment that reveals just how shocking the Blob was for scientists.

A decade ago, marine heat waves were not a phenomenon sanctuary scientists were fully aware of, said Danielle Lipski, a NOAA ecologist who oversaw the condition report.

The foundation species that creates habitat for everything else in the Greater Farallones is bull kelp, a seaweed that grows from the seafloor to the surface in dense forests. Before the Blob, Ms. Lipski and her colleagues hadn’t thought bull kelp would be particularly vulnerable to climate change.

By the time the Blob dissipated, more than 90 percent of Northern California’s kelp forests were gone.

Historically, kelp has had booms and busts, Ms. Lipski said. “We just thought that’s the pattern for kelp — it’ll recover,” she said. “And it hasn’t.”