Quantifying Anthropogenic Influences on Global Wave Height Trend During 1961-2020 With Focus on Polar Ocean

Abstract

This study investigates the contribution of external forcings on global and regional ocean wave height change during 1961-2020. Historical significant wave height (H-s) produced for different CMIP6 external forcings and preindustrial control conditions following the Detection and Attribution Model Intercomparison Project (DAMIP) are employed. The internal variability ranges are compared with different external forcing scenario. Statistically significant linear trends in H-s computed over regional ocean basins are found to be mostly associated with anthropogenic forcings: greenhouse gas-only (GHG) and aerosol-only (AER) forcing. For H-s, GHG signals are robustly detected and dominant for most of the global ocean, except over North pacific and South Atlantic, where AER signals are dominant. These results are supported by multi-model analysis for wind speed. The remarkable increase in H-s over the Arctic (22.3%) and Southern (8.2%) Ocean can be attributed to GHG induced sea-ice depletion and larger effective fetch along with wind speed increase. Plain Language Summary We quantify the influence of anthropogenic forcings (greenhouse gas-only and aerosol-only forcing) and natural forcing to the significant wave height trends during 1961-2020 using CMIP6 individual forcing experiments. It is shown that anthropogenic influence is majorly responsible for the significant wave height changes and natural (solar and volcanic activities) forcings show limited influence. The human-induced greenhouse gas increases are found to be the dominating factor for most of the global ocean, whereas anthropogenic aerosols are the dominating forcing for a few ocean basins, such as North Pacific and South Atlantic. The multimodel analysis for wind speed corroborates the relative dominance of signals in wave height change. In the polar ocean (Arctic and Southern Ocean), we see exceptional wave height increase compared to other regions. Sea-ice decline associated with greenhouse gas forcing provides larger fetch for the waves to grow in polar region. Moreover, the contrasting influence of greenhouse gas and aerosol forcing to sea-ice area and wind speed changes are shown to drive the total wave height changes.