Waves Along California’s Coast Are Getting Bigger, Study Says

Early this year, severe storms battered California, bringing huge waves that damaged infrastructure and forced people away from the coast. That may be the new norm, as climate change fuels severe weather that is making waves bigger, according to a study published this month.

The study, published in the Journal of Geophysical Research: Oceans, uses nearly a century of seismic records to show that mean winter wave heights, as well as the frequency of big waves, have significantly increased along California’s coast since the 1970s.

In recent decades, the number of waves taller than 16 feet has more than doubled, according to the paper, which showed that the Aleutian Low, an area of low pressure over the Aleutian Islands in southwest Alaska, has also intensified, likely increasing storms. The findings add to a growing body of research linking climate change with extreme weather, including the storms that generate colossal waves.

“If the storms increase in intensity, you have stronger winds, and stronger winds make bigger waves,” said Peter D. Bromirski, the author of the paper and an oceanographer at the University of California, San Diego.

In order to determine the wave heights, Dr. Bromirski analyzed 90 years of seismic records archived at a lab that monitors earthquake activity at the University of California, Berkeley. Ocean waves can generate signals, not unlike those of earthquakes, when two collide as they are moving in opposite directions collide (one as it is approaching the shore, the other, as it is moving away). That collision sends a signal to the ocean floor, generating seismic waves that can be detected by seismographs — the same instruments used for monitoring earthquakes.

In the 1980s, the National Oceanic and Atmospheric Administration installed buoys that can determine wave height using an accelerometer, which measures how much a buoy moves up and down. But those records did not go back far enough. Understanding the effects of climate change requires several decades of information, including those preceding the 1970s, when the world began to heat up, Dr. Bromirski said.

The records showed a “significant increase in both the mean winter wave heights and the number of large, strong wave events,” he said, noting that extended lulls in strong winter wave activity have also largely disappeared.

While the study’s methodology is unique, it is not the first to explore the effect of climate change on the ocean’s waves. In 2014, Canadian researchers used sea level pressure to model future wave heights, finding that the frequency of extreme waves could double or triple in several coastal regions around the world. A 2019 study by researchers at the University of California, Santa Cruz, found that the rising sea-surface temperatures were influencing global wind patterns, and making waves stronger. Another 2019 study showed that high emissions could create the conditions for bigger waves.

Some researchers who were not involved in the latest study said that while the connections between climate change and sea-level rise have been well established, Dr. Bromirski’s paper added to research showing that waves, too, can contribute to worsening flooding, erosion and damage along the coast.

“What this shows is that in addition to flood risks being amplified by sea level rise, it can also be amplified by the fact that waves are increasing,” said Patrick Barnard, a research geologist with the United States Geological Survey. “That’s a factor that we have to consider as well as we plan to create resilient communities in the face of rising — not just sea levels but also rising levels during storms.”

Ian Young, a professor of oceanography at the University of Melbourne, in Australia, said that Dr. Bromirski’s conclusions were consistent with previous research using satellite data from the 1980s to study wave heights, and helped to show that the changes had been occurring over a longer period. “There is clearly a long-term trend,” he said.

Those changes were apparent early this year, when one atmospheric river after another battered the West Coast. The severe weather left homes in Santa Cruz, Calif., damaged by flooding and wind. Several months later, a landslide caused homes in one of Los Angeles County’s most affluent neighborhoods to collapse into a canyon. And when it comes to the waves, a sudden deluge can overwhelm coastal areas, destroy infrastructure and contribute to erosion.

Even pro surfers worry: Bigger is not always better.

“If the waves are huge, but it’s stormy and windy with chop, surfers are not going to be able to surf those waves,” Tyler Fox, a big wave surfer in Santa Cruz, said of ocean conditions that can include many small waves that make the water’s surface rough.

Mr. Fox, 42, has been surfing for more than three decades, and said that there are some spots where, at high tide, it is no longer possible to enter the water. In other places, he said, sections of cliff have calved off into the water, creating new hazards. Violent storms can also hurl the debris from damaged trees, homes and other structures into the ocean, he said, “basically into my sanctuary, a place that I love.”

Livia Albeck-Ripka is a reporter for The Times based in California. She was previously a reporter in the Australia bureau. More about Livia Albeck-Ripka

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