Smog is blocking sunlight in China and making much of the country significantly darker than it was half a century ago.

Using nearly 500 instruments spread throughout the country that record the amount of sunlight reaching the ground, researchers found that solar radiation has decreased by about 2 percent per decade since 1954.

The country is roughly 10 percent darker on average than it was 50 years ago.

Fewer clouds

The researchers also found that water evaporation rates across the country have decreased in the same period, by about 1.5 inches per decade. The dip in solar radiation, combined with other factors such as increased temperatures and wind speeds, are likely behind this trend, said lead researcher Yun Qian from Pacific Northwest National Laboratory(PNNL) in Washington.

Adding further support to this hypothesis is that cloud cover, the other likely explanation, has actually decreased in China over the past half century, by 0.78 percent each decade.

Eliminating clouds from the dimming equation leaves little doubt that fossil fuel emissions, which have increased by nine-fold in the past half-century, is blanketing China in a foggy haze that absorbs and deflects sunlight, the researchers say.

Will get worse

China’s expected increase in economic activity will only make the situation worse and could lead to other problems as well, Qian said.

"Haze doesn't just block the solar radiation," Qian said. "It is also infamous for acid rain and respiratory diseases."

The study was detailed online recently by the journal Geophysical Research Letters.

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