It has been recognized since the dawn of global seismology that the oceans produce a planet-wide continuous and seasonally varying microseism signal.  Extensive standardized global digital seismographic network archives such as the Global Seismographic Network (GSN) and GEOSCOPE now facilitate the uniform analysis of microseism energy across nearly four decades, including the signature of anthropogenic climate change. The globally observable primary microseism signal near 20–14 s period as sensed by long-operational seismic stations is a particularly apt proxy for global near-coastal wave energy because it is produced by propagating ocean wave seafloor tractions applied at depths of less than about 300 meters and is less sensitive to ocean wave and bathymetric complexities that influence energetic and more widely studied secondary microseism signal. Examining continuous digital vertical component seismic records (principally sensing large-scale Rayleigh waves) beginning in the late 1980s, a robust secular trend estimation procedure reveals highly significant and geographically correlated increasing primary microseism amplitudes and energies at 41 of 52 long-running GSN stations. The greatest absolute rates of increase are observed for station PMSA on the Antarctic Peninsula with seismic (acceleration) amplitude and (velocity-squared) energy trends through August 2022 (±3σ confidence intervals) 0.36±0.08 %/y relative to the long-term station median) and 4.16±1.07 (nm/s)2/y (0.58±0.15 %/y), respectively. Assuming linearity and stationary ocean wave-seismic wave coupling, the corresponding inferred rate near-coastal ocean wave energy increase sensed by this constellation of stations is 0.27±0.03 %/y for the full record and 0.35±0.04 %/y since the turn of the 21st century. These inferred rates of ocean wave intensification compare well with independent estimates from oceanographic and meteorological data. Time-smoothed (e.g., 2-month) primary microseism signal station histories regionally cluster out to thousands of kilometers of geographic separation, demonstrating very large-scale sampling of ocean wave forces and propagation of Rayleigh waves.  Multi-year primary microseism signal variations also correlate well with El Niño and La Niña conditions that affect the general distribution of large-scale storm energy in the Pacific region, with increasing energy in the southwest Pacific under positive El Niño-Southern Oscillation (ENSO) and in the southeast Pacific under negative ENSO (positive Southern Oscillation; SOI) climate index conditions. Similar analysis of the (much stronger) 5–12 s period secondary microseism signal shows consistent but higher variance temporal and geographic trends that reflect the complexities of the ocean depth and wave-wave interference conditions necessary for its excitation.  These now almost 40-year near-continuous time series contain deep information on the history of ocean waves.  For example, primary - secondary histories display station-specific seasonal phase and amplitude relationships reflecting station-specific seasonal ocean wave variability that can provide further insight into annual variability in ocean wave state and can be analyzed down to the hourly level to assess statistics for extreme wave events.

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