A significant increase in wave height in the North Atlantic Ocean over the 20th century

• A new wave hindcast starting in 1900 is developed for the North Atlantic Ocean.
• This hindcast is validated against Voluntary Observing Ship data and altimetry.
• A significant increase in yearly-mean wave height is shown to the North of the region.
• This increase in wave height constitutes a new hypothesis to explain coastal erosion.

A new 109 year numerical wind-wave hindcast is developed for the North Atlantic Ocean based on the 20th century atmospheric reanalysis (20CR). Wave results are validated directly against data originating from voluntary observing ships and satellite altimetry in the North-East Atlantic Ocean. The normalized error for yearly-mean significant wave height (Hs) is shown to be of the order of 5% for the second part of the 20th century. An indirect validation is also performed through 10 m wind speed and suggests that the accuracy of yearly-mean Hs only slightly decreases for the beginning of the 20th century. The comparison between Hs and the index of the North Atlantic Oscillation revealed that this phenomenon partly controls Hs inter-annual variability, with a positive (negative) correlation in the northeastern (southwestern) part of the study area. The analysis of model results shows an increase in Hs over the whole North Atlantic Ocean superimposed to the inter-annual variability, reaching 0.01 m.yr− 1 (20 to 40% over the 20th century) north of 50°N. This increase is explained by a rise in wind speed exceeding 20% north of 50°N. The roughening in the wave climate demonstrated in this study is expected to have strong implications for the development of coastal zones and could explain the increase in erosion along the North Atlantic shorelines.