To predict future coastal hazards, it is important to quantify any links between climate drivers and spatial patterns of coastal change. However, most studies of future coastal vulnerability do not account for the dynamic components of coastal water levels during storms, notably wave-driven processes, storm surges and seasonal water level anomalies, although these components can add metres to water levels during extreme events. Here we synthesize multi-decadal, co-located data assimilated between 1979 and 2012 that describe wave climate, local water levels and coastal change for 48 beaches throughout the Pacific Ocean basin. We find that observed coastal erosion across the Pacific varies most closely with El Niño/Southern Oscillation, with a smaller influence from the Southern Annular Mode and the Pacific North American pattern. In the northern and southern Pacific Ocean, regional wave and water level anomalies are significantly correlated to a suite of climate indices, particularly during boreal winter; conditions in the northeast Pacific Ocean are often opposite to those in the western and southern Pacific. We conclude that, if projections for an increasing frequency of extreme El Niño and La Niña events over the twenty-first century are confirmed, then populated regions on opposite sides of the Pacific Ocean basin could be alternately exposed to extreme coastal erosion and flooding, independent of sea-level rise

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The El Niño-Southern Oscillation is the dominant mode of interannual climate variability across the Pacific Ocean basin, with influence on the global climate. The two end members of the cycle, El Niño and La Niña, force anomalous oceanographic conditions and coastal response along the Pacific margin, exposing many heavily populated regions to increased coastal flooding and erosion hazards. However, a quantitative record of coastal impacts is spatially limited and temporally restricted to only the most recent events. Here we report on the oceanographic forcing and coastal response of the 2015–2016 El Niño, one of the strongest of the last 145 years. We show that winter wave energy equalled or exceeded measured historical maxima across the US West Coast, corresponding to anomalously large beach erosion across the region. Shorelines in many areas retreated beyond previously measured landward extremes, particularly along the sediment-starved California coast.

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Erosion, caused in large part by unusually severe storms, has damaged beaches and property in recent years along the Pacific coast of the United States. In the Pacific Northwest (Oregon and Washington), four storms were experienced during the 1998–1999 La Niña winter that produced wave heights which exceeded what had been projected as the 100‐year extreme event. This occurrence raises questions about the effects of climate controls— such as El Niños and La Ni˜nas—on wave conditions in the North Pacific, and whether there has been a progressive increase in wave heights during recent decades, much as has been found in the North Atlantic. In the North Atlantic, researchers have documented from a long‐term record of wave measurements west of Lands End, England, that wave heights have increased progressively since the late 1960s [Carter and Draper, 1988; Bacon and Carter, 1991; Kushnir et al., 1997; Gulev and Hasse, 1999]. Previous to our study, no attempt had been made to examine whether such trends exist in the North Pacific. This is now possible, thanks to more than a quarter‐century of ocean buoy measurements of daily wave conditions throughout the eastern North Pacific.