California Braces for Increased Coastal Erosion as Kelvin Waves Arrive

A significant pulse of wave energy, known as a Kelvin wave, generated by El Niño conditions is traveling up the West Coast, leading to a rise in sea levels and an increased risk of coastal erosion for communities along the shore. The phenomenon is expected to raise sea levels by up to one foot this month, posing dangerous conditions for humans and marine wildlife.

Kelvin waves are planetary waves, large and slow-moving masses of water that can span thousands of miles. Named after physicist Lord Kelvin, these waves are not the same as typical beach waves. They involve warm water moving along the equator toward the Americas, subtly raising sea levels. While the surface change might not be dramatic, a few centimeters higher than normal, it can have a substantial impact when combined with other factors. "If you add that sea level change to the normal tides or strong tide, and then potentially add a storm on top of it, which El Niño intensifies, then it can start to have a meaningful effect on changing the beach erosion and flooding at the coast," said Paul Roundy, professor of atmospheric science at the University at Albany.

This season has already seen several Kelvin waves affect the West Coast. Coastal towns in California, including Malibu, Laguna Beach, and Long Beach, have experienced significant erosion due to a combination of factors, including El Niño and Pacific hurricanes. In response to the potential impacts of El Niño, California Governor Gavin Newsom declared a state of emergency in late September to prepare the state.

The last strong El Niño event, from 2015-2016, produced five Kelvin waves. In contrast, the 2022-2023 El Niño did not generate strong Kelvin waves due to less favorable conditions, such as weak westerly winds.

Kelvin waves commonly occur during El Niño years. This occurs when the trade winds that typically push warm surface water toward the western Pacific weaken or shift direction, causing warm water to move eastward and initiate a Kelvin wave. Scientists are debating the impact of climate change on El Niño events. However, El Niño years tend to see higher global temperatures as warm ocean water releases heat into the atmosphere. Combined with existing record-breaking global temperatures attributed to human-caused climate change, scientists anticipate that 2027 is likely to be the hottest year on record globally.