Increasing ocean wave energy observed in Earth's seismic wavefield since the late 20^th century

Ocean waves excite continuous globally observable seismic signals. We use data from 52 globally distributed seismographs to analyze the vertical component primary microseism wavefield at 14-20 s period between the late 1980s and August 2022. This signal is principally composed of Rayleigh waves generated by ocean wave seafloor tractions at less than several hundred meters depth, and is thus a proxy for near-coastal swell activity. Here we show that increasing seismic amplitudes at 3σ significance occur at 41 (79%) and negative trends occur at 3σ significance at eight (15%) sites. The greatest absolute increase occurs for the Antarctic Peninsula with respective acceleration amplitude and energy trends ( ± 3σ) of 0.037 ± 0.008 nm s^-2y^-1 (0.36 ± 0.08% y^-1) and 4.16 ± 1.07 nm² s^-2y^-1 (0.58 ± 0.15% y^-1), where percentage trends are relative to historical medians. The inferred global mean near-coastal ocean wave energy increase rate is 0.27 ± 0.03% y^-1 for all data and is 0.35 ± 0.04% y^-1 since 1 January 2000. Strongly correlated seismic amplitude station histories occur to beyond 50^∘ of separation and show regional-to-global associations with El Niño and La Niña events.