On the roles of circulation and aerosols in the decline of mist and dense fog in Europe over the last 30 years
Surface solar radiation has undergone decadal variations since the middle of the twentieth century, producing global 'dimming' and 'brightening' effects super(2). These variations presumably result from changes in aerosol burden and clouds super(3), but the detailed processes involved have yet to be determined. Over Europe, the marked solar radiation increase since the 1980s is thought to have contributed to the observed large continental warming super(4), but this contribution has not been quantified. Here we analyse multidecadal data of horizontal visibility, and find that the frequency of low-visibility conditions such as fog, mist and haze has declined in Europe over the past 30 years, for all seasons and all visibility ranges between distances of 0 and 8 km. This decline is spatially and temporally correlated with trends in sulphur dioxide emissions, suggesting a significant contribution of air-quality improvements. Statistically linking local visibility changes with temperature variations, we estimate that the reduction in low-visibility conditions could have contributed on average to about 10-20% of Europe's recent daytime warming and to about 50% of eastern European warming. Large improvements in air quality and visibility already achieved in Europe over the past decades may mean that future reductions in the frequency of low-visibility events will be limited, possibly leading to less rapid regional warming.