California waves grow with climate change – 9/1/2023 – Environment

Earlier this year, California was hit by strong storms, with huge waves that damaged infrastructure and forced people to stay away from the coast. According to a study published this month, this situation could become the new normal, because climate change feeds the bad weather that is making the waves bigger.

Published in the Journal of Geophysical Research: Oceans, the study uses nearly a century of seismic data to show that average winter wave height and frequency of big waves have been increasing significantly off the Californian coast since the 1970s.

In recent decades, the number of waves over five meters high has more than doubled, according to the article, which showed that the Aleutian Low, an area of ​​low pressure over the Aleutian Islands in southwest Alaska, has also intensified, probably resulting in more storms.

The findings add to a growing body of studies linking climate change to extreme weather phenomena, including storms that generate colossal waves.

“If storms increase in intensity, we get stronger winds, and stronger winds create bigger waves,” explained Peter D. Bromirski, author of the paper and an oceanographer at the University of California San Diego.

To determine the height of the waves, Bromirski analyzed 90 years of seismic records archived in a laboratory at the University of California at Berkeley that monitors earthquake activity.

Ocean waves can generate signals, not unlike earthquake signals, when two waves collide when moving in opposite directions (one approaching the shore and one moving away). This collision transmits a signal to the seabed, generating seismic waves that can be detected by seismometers — the same instruments used to monitor earthquakes.

In the 1980s, the National Oceanic and Atmospheric Administration (NOAA) installed buoys that can determine wave heights using an accelerometer, which measures the up and down movement of a buoy. But these records didn’t start early enough.

According to Bromirski, understanding the effects of climate change requires several decades of information, including data prior to the 1970s, when the world began to warm.

The records revealed “a significant increase in both the average winter wave height and the number of big, strong wave events,” he said, noting also that the extended lull phases between strong wave activity in winter had also largely disappeared. .

Although the methodology used is unique, the study is not the first to measure the effect of climate change on ocean waves.

In 2014 Canadian researchers used sea level pressure to model future wave heights, concluding that the frequency of occurrence of extreme waves could double or triple in various coastal regions of the world.

A 2019 study by researchers at the University of California, Santa Cruz concluded that rising sea surface temperatures are influencing global wind patterns and strengthening waves. Another 2019 study indicated that high gas emissions can create the conditions for larger waves.

Some scientists not involved in the latest study said that while the links between climate change and sea level rise have been well established, Bromirski’s paper adds to research showing that waves can also contribute to worsening flooding, erosion and coastal damage.

“What this shows is that in addition to flood risks being amplified by rising sea levels, they can also be amplified by the fact that waves are rising,” said Patrick Barnard, a research geologist with the US Geological Survey.

“This is yet another factor we need to take into account when planning to build resilient communities in the face of rising sea levels and increased waves during storms.”

Ian Young, professor of oceanography at the University of Melbourne in Australia, said Bromirski’s conclusions were in line with previous research that used satellite data from the 1980s to study wave heights and helped show that changes had already been happening for a long time. more time.

“It’s clear that this is a long-term trend,” he said.

These changes were evident earlier this year, when the west coast of the US was buffeted by one atmospheric river after another. Bad weather has left homes in Santa Cruz, Calif., damaged by floods and winds.

A few months later, a landslide caused homes in one of Los Angeles County’s wealthiest neighborhoods to collapse into a canyon. In the case of waves, a sudden flood is capable of flooding coastal areas, destroying infrastructure and contributing to erosion.

Even professional surfers worry: For them, bigger waves aren’t always better.

“If the waves are huge, but there’s a storm and a strong wind, surfers aren’t going to be able to ride those waves,” said Tyler Fox, a big-wave surfer in Santa Cruz, speaking of ocean conditions that can include lots of small waves that churn up the surface. from water.

Fox is 42 years old and has been surfing for over three decades. He said that there are some places where it is no longer possible to enter the water when the tide is high. Elsewhere, he said, cliff sections have fallen into the water, creating new hazards. Violent storms can also throw debris from broken trees, houses and other structures into the sea, “basically my sanctuary, the place I love,” he said.

_{Translated by Clara Allain}