We have been alerted to yet another research paper that documents the complexity of the human role in the climate system (h/t to Erik). It is
Robert Vautard, Pascal Yiou and Geert Jan van Oldenborgh: 2010: Decline of fog, mist and haze in Europe over the past 30 years. Nature Geosciennces. 18 January 2009 DOI: 10.1038/NGEO414.
The abstract reads
“Surface solar radiation has undergone decadal variations since the middle of the twentieth century, producing global ‘dimming’ and ‘brightening’ effects. These variations presumably result from changes in aerosol burden and clouds3, 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, 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.”
Text in the conclusion reads
“Unfortunately, current regional climate models are probably not ready to reproduce the physics underlying these trends, because a fully integrated representation of the atmosphere, with surface processes, microphysics coupled with aerosols and gasphase chemistry models, with relatively high resolution, is required. Also required are databases of the long-term evolution of land use, anthropogenic heat fluxes, aerosol anthropogenic and natural gas species and aerosol emissions. As yet, state-of-the-art regional aerosol models have been shown not to be able to simulate with sufficient skill the total aerosol burden over Europe. Simulating trends in low-visibility phenomena, and their impact on climate, therefore remains an open challenge for models.”
This paper documents a particular major role of aerosols in regional climate, and also the inability of current climate models to skillfully simulate (much less predict) this effect.