Earth's global seismic background between periods of about 4–20 s results from wave activity in the oceans. This wavefield is excited by two distinct source mechanisms. The primary microseism (approximately 14–20 s period) is generated by direct ocean wave-ocean floor forces confined to shallower ocean depths near coasts and oceanic islands. The approximately 100 times stronger secondary microseism (approximately 4–10 s period) is generated by interfering waves that create depth- and period-dependent seafloor pressures and generates a seismic signal at half the period of the causative ocean waves. We evaluate the period-dependent amplitudes of the microseism observed at 73 long-operating seismic stations distributed from the South Pole to northern Canada between the late 1980s and August of 2024. Analysis of primary and secondary microseism seismic amplitudes reveals 58 (79%) and 48 (65%) stations that show significant positive trends, respectively, showing positive average rates of primary and secondary amplitude of 0.15±0.0 and 0.10±0.05 %/yr in amplitude and 0.25±0.08 and 0.14±0.09 %/yr in energy, respectively, at 99% confidence. Global rates of microseism amplitude increase are highest at the longest seismic periods. This is consistent with a slight increase in the largest storm systems that generate the longest-period ocean waves.