Vautard et al. calculated global brightening’s contribution to European warming.
“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 clouds, 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 analyze 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.”
Is anyone aware of additional studies measuring global brightening’s contribution to warming on a global scale?
- Dana1981Lv 71 decade agoFavorite Answer
Yes, see Wild et al. (2007).
As it so happens, I'm working on a Skeptical Science rebuttal on a very similar topic (mid-century cooling, due to global dimming). It should be published in the next day or two, but you can see the work in progress here:
Though I'm focusing more on the dimming than brightening, my sense is that the brightening has had very little impact on a global scale. As you can see in the figures linked in my article, global sulfate emissions haven't declined very much, but rather have been relatively flat since around 1975. My sense is that it's not so much global brightening as stopping the rapid acceleration of global dimming.
While some developed regions like Europe have reduced their sulfate emissions, the emissions from developing regions (like China) have increased. So while some regions will experience warming temperatures due to brightening, others will experience regional cooling (or more accurately, suppressed warming) due to dimming.
On a global scale, the mid-century dimming had a roughly 0.6°C cooling effect, but since about 1975, it's been relatively stable, likely less than a tenth of a degree of a warming effect globally.