Aerosols, weather and climate

Andreas Sterl, KNMI

Europe is warming much faster than the global mean. One hypothesis to explain this is that due to the cleaner air in Europe more solar radiation reaches the surface. This presentation reviews the temporal evolution of aerosol concentrations and their impact on weather and climate.

Aerosols, tiny particles floating in the air, have a profound impact on health, weather and climate. Since the 1970s, clean air policies have substantially reduced the aerosol burden in North America and Europe. Today, the air in western Europe is probably cleaner than at any point in time since the beginning of the 20th century. The effects are clearly visible in our weather. We have less clouds, more sunshine, less fog and better visibility than only a few decades ago. However, more sunshine leads to an extra warming on top of the greenhouse effect.

The largest impact of aerosols on climate is through their impact on clouds. As clouds are among the least understood aspects of climate change, the amount of extra warming due to aerosol reduction is highly uncertain. Available evidence suggests a global cooling effect of ~0.5 K caused by the present-day aerosol loading, while over Europe the aerosol reduction has lead to 0.5-1 K extra warming since the 1970s.