California’s Winter Waves Getting Bigger Due to Climate Change, Study Finds

California is known for its consistently sunny weather, progressive politics, movie making and the gigantic, rolling waves that crash against its iconic coastline.

According to a new study, however, the climate crisis is making those waves even bigger.

The study, conducted by Peter Bromirski — University of California, San Diego (UCSD), Scripps Institution of Oceanography researcher emeritus — showed that, on average, California’s colossal winter waves have gotten bigger due to climate change, a press release from UCSD said.

“Waves ride on top of the sea level, which is rising due to climate change,” said Bromirski in the press release.

Bromirski used data collected over almost a century to demonstrate the winter wave height increases. The changes will affect coastal communities, infrastructure and biosystems, the study said.

“As sea level rise progresses, the impacts of wave activity will be aggravated, resulting in increased coastal erosion and flooding of low lying regions. These issues are particularly problematic along the California coast, where vulnerable sea cliffs will experience increasing wave impacts. Because of sea level rise, projections at the end of the twenty-first century indicate that even moderate waves will produce coastal impacts comparable to recent extreme winter wave events,” Bromirski wrote in the study.

The study, “Climate-Induced Decadal Ocean Wave Height Variability From Microseisms: 1931–2021,” was published in the Journal of Geophysical Research: Oceans.

Previous research suggests that climate change has caused an increase in North Pacific Ocean storm activity, according to the press release. Bromirski looked at seismic records from 1931 to 2021 in order to infer the height of waves, a technique Bromirski developed.

The acceleration of global warming and increasing winter wave heights could significantly impact erosion and flooding along coastal California, which is already facing rising sea levels.

Bromirski said that as waves reach waters along the coast, some of their energy goes back out to sea. When this energy meets approaching waves, downward pressure created by their interaction becomes seismic energy on the ocean floor. This energy makes its way inland as seismic waves that can be picked up by seismographs. How strong these seismic signals are directly reflects wave height, which Bromirski was able to calculate from decades of data.

“When sea levels are elevated even further during storms, more wave energy can potentially reach vulnerable sea cliffs, flood low-lying regions, or damage coastal infrastructure,” Bromirski said.

In the calculations, Bromirski filtered out the seismic activity of actual earthquakes, which usually don’t last nearly as long as storm-induced ocean waves.

Wave height-measuring buoys along the California coast have only been around since about 1980, but Bromirski was interested in the decades before 1970, which was when global warming started to really speed up.

Bromirski used seismograph readings from UC Berkeley digitized from analog sheets by graduate students in order to look for patterns across decades.

Bromirski’s analysis of the data showed that, after 1970, the average California winter wave height increased by 13 percent — about one foot — as compared to the average height from 1931 to 1969. Bromirski also discovered that about twice as many storms with waves taller than 13 feet occurred along the California coast from 1996 to 2016 as compared to the period from 1949 to 1969.

“After 1970, there is a consistently higher rate of large wave events,” Bromirski said in the press release. “It’s not uncommon to have a winter with high wave activity, but those winters occurred less frequently prior to 1970. Now, there are few winters with particularly low wave activity. And the fact that this change coincides with the acceleration of global warming near 1970 is consistent with increased storm activity over the North Pacific resulting from climate change.” 

If the average winter wave heights along the coast of California keep getting bigger with climate change, it could increase the impacts of sea-level rise.

Bromirski compared the results of the study with North Pacific atmospheric patterns, since that is where winter storms and waves usually originate. Bromirski wanted to know if the Aleutian Low — a semi-permanent winter low pressure system near Alaska’s Aleutian Islands — had gotten stronger in modern times, since an intensified Aleutian Low usually means an increase in storm intensity and activity. The results were that the Aleutian Low had generally intensified since 1970.

“That intensification is a good confirmation that what we are seeing in the wave record derived from seismic data is consistent with increased storm activity,” Bromirski said in the press release. “If Pacific storms and the waves they produce keep intensifying as climate change progresses and sea level rises, it creates a new dimension that needs to be considered in terms of trying to anticipate coastal impacts in California.”