In the late 1980s and 1990s, researchers at ETH Zurich discovered the first indications that the amount of sunlight reaching the Earth’s surface had been steadily declining since the 1950s.
In the late 1980s and 1990s, researchers at ETH Zurich discovered the first indications that the amount of sunlight reaching the Earth’s surface had been steadily declining since the 1950s. The phenomenon was known as “global dimming”. However, a reversal in this trend became discernible in the late 1980s. The atmosphere brightened again at many locations and surface solar radiation increased.
“In previous studies, we showed that the amount of sunlight that reaches the Earth’s surface is not constant over many decades but instead varies substantially – a phenomenon known as global dimming and brightening,” says ETH Professor Martin Wild of the Institute for Atmospheric and Climate Science.
Natural variations or air pollution?
Yet little is known about the reasons for these fluctuations, which have been observed for decades. One particularly controversial point is whether the fluctuations are caused by air pollution, with aerosols blocking the sunlight, or whether they are a result of natural variations in the climate system.
A number of scientists suspected that cloud cover may have changed over the years, absorbing the sun’s rays more effectively during the dimming phase than during the brightening phase.
Read more at ETH Zurich
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