SAN DIEGO — The average height of winter waves along parts of the California coast have increased by as much as 1 foot since 1970 largely due to climate change, increasing the threat of sea cliff collapses, according to a new study by UC San Diego.
The study, which heavily focuses on central California, also found that storms generating waves at least 13 feet tall now occur, on average, 23 times each winter, more than double what it was from 1949 to 1969.
“The dividing line was 1970, when global warming began to accelerate,” said Peter Bromirski, a researcher at UCSD’s Scripps Institution of Oceanography and the lead author of the paper, which was published Tuesday in the Journal of Geophysical Research-Ocean.
“Warming puts more energy into the atmosphere, and you end up with stronger storms, which produce stronger winds and higher waves,” he said.
The study’s publication follows an extremely stormy winter that replenished reservoirs and reduced the risk of wildfires while also causing serious damage from one end of the state to the other, notably along the coast.
Storms triggered landslides in the Big Sur area that closed parts of Highway 1 for months, whipped up waves that largely destroyed the Capitola Wharf near Santa Cruz, and produced a dangerous bluff collapse in the Blacks Beach section of La Jolla.
The storms came as Bromirski was finishing his examination of historic wave heights, a study largely based on seismic records.
When waves reach shore some of their energy is reflected back into the sea, he said. That energy interacts with other incoming waves, producing a pressure signal that turns into seismic waves at the seafloor. Those signals are directly related to the height of each wave.
The new study was primarily focused on central California, which often takes a beating from winter storms out of the North Pacific. Bromirski said that the average height of the waves in that area began to increase after 1970 and had reached 8.5 feet in recent years. Before 1970, the average height was 7.5 feet.
He did not compute the average winter wave height for Southern California but said that climate change also is affecting the size of the surf along that state’s entire coastline.
