Uncertainties in air–sea heat flux data sets are too large to allow detection of the change in global mean net air–sea heat flux, on the order of 0.5 W m–2 since 1971, required for consistency with the observed ocean heat content increase. The accuracy of reanalysis and satellite observation based freshwater flux products is limited by changing data sources. Consequently, the products cannot yet be reliably used to directly identify trends in the regional or global distribution of evaporation or precipitation over the oceans on the time scale of the observed salinity changes since 1950.
Basin scale wind stress trends at decadal to centennial time scales have been observed in the North Atlantic, Tropical Pacific, and Southern Oceans with low to medium confidence. These results are based largely on atmospheric reanalyses, in some cases a single product, and the confidence level is dependent on region and time scale considered. The evidence is strongest for the Southern Ocean for which there is medium confidence that zonal mean wind stress has increased in strength since the early 1980s.
There is medium confidence based on ship observations and reanalysis forced wave model hindcasts that mean significant wave height has increased since the 1950s over much of the North Atlantic north of 45°N, with typical winter season trends of up to 20 cm per decade.