Abstract
The long-term historical trends in global wave energy systems are investigated using 42-year wave reanalysis from 1979 to 2020. In addition to the historical trend of omnidirectional wave power, trends of period-resolved and period-directionally resolved wave energy systems are estimated using spectral partitioned wave parameters and linked to commensurate trends in the historical wind speed. The present study shows that opposing trends in distinct wave energy systems offset each other in many oceans, e.g., the equatorial Pacific Ocean, North Atlantic Ocean, and Indian Ocean, where shorter period waves (<11 s) have decreased while the longer period waves (11–15 s) have increased. These mixed trends in the wave energy systems create the appearance or artifact of neutral or insignificant trends for about 45 % of global oceans and seas. In the present study, the global wave energy climate changes are classified into six types based on the mixed trends in the wave energy systems, which reveals that more than ninety percent of the global wave sites are experiencing significant changes in wave energy systems and climates. It highlights the need for increased scrutiny of risks for coastal and ocean communities and design practices to ensure the resilience of coastal defense and other marine energy infrastructure, e.g., offshore wind and wave energy farms.