Formation of the North Atlantic Warming Hole by reducing anthropogenic sulphate aerosols

The North Atlantic Warming Hole (NAWH) has been observed and predicted due to the increase in carbon dioxide (CO₂) concentration. If sulphate aerosols, which have a cooling effect on the atmosphere, are reduced by air pollution control, the NAWH may form as it would if CO₂ concentrations increased. In this study, sensitivity experiments using a coupled atmosphere–ocean-aerosol model were conducted by varying the amount of sulphur dioxide (SO₂) emissions, a precursor of sulphate which is the primary anthropogenic aerosol in the atmosphere, to analyse the changes in the ocean temperature, salinity, and density. The results showed that although the spatial patterns of the NAWH due to the changes in SO₂ emissions was similar to that due to the changes in the CO₂ concentrations, the magnitude of the shifts in the ocean parameters due to the changes in SO₂ emissions is larger even when changes in global mean temperature are comparable. This can be due to the spatial concentration of sulphate aerosols in the mid-latitudes of the Northern Hemisphere, resulting larger changes in the heat transport from the south on the Gulf Stream and the North Atlantic Current along with changes in freshwater inflow from the Arctic through the Labrador Sea.