Aerosols emanating from vehicles and industrial plants reflect sunlight and have been linked to a cooling trend from the 1950s to the 1970s. A team led by Rolf Philipona of the Swiss federal agency MeteoSwiss has now quantified the reverse trend — warming caused by solar radiation shining through cleaner skies, which has occurred since the early 1980s.
They measured short-wave radiation, temperature and humidity near ground level at 25 sites in Switzerland and 8 in Germany, and then derived values for long-wave radiation, including heat radiating from the ground. The data indicate that the warming attributable to incoming short-wave radiation — and thus to fewer aerosols in the atmosphere — accounts for two-thirds of the overall warming of the past two decades. This totals about 1 °C in Europe.