The average height of waves has increased as much as one foot since 1970, according to a new study by the University of California San Diego. That’s a 13% increase—and you can thank climate change for the bigger waves.

Perhaps even more concerning, the number of megawaves, measuring 13 feet or more has doubled compared to the two-decade period spanning from 1949 to 1969.

“After 1970, there is a consistently higher rate of large wave events,” said Peter Bromirski, UC San Diego Scripps Institution of Oceanography researcher emeritus, in a statement. “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.”

Warmer temperatures put more energy into the atmosphere, he explains, which result in strong storms. Those, in turn, bring about bigger waves and stronger winds.

California has been walloped by a series of storms in the past year. Atmospheric rivers, a meteorological term that few were familiar with before the string of storms, are bands of moisture that act like a fire hose when they hit land, dumping rain and snow for thousands of miles. The parade of storms in 2023 helped cut the drought in California, but resulted in widespread flooding throughout the state. Some areas of the state received nearly 40 inches of rain. Downtown Los Angeles saw over 25 inches. And in San Diego County, more rain fell in the first three months of 2023 than in all of 2022.