Pollution Darkened China’s Skies


Records from more than 500 weather stations across China for the years 1954 to 2001 indicate China has darkened over the past half-century. Where has all the sunshine gone? The usual suspect, at least to a climatologist, would be cloud cover. But in the most comprehensive study to date of overcast versus cloud-free days in China, a team of researchers from the Department of Energy’s Pacific Northwest National Laboratory, reporting in the current advance online issue of Geophysical Research Letters, has found that cloud cover has been decreasing for the past 50 years. Less cloud cover and more cloud-free skies, regardless of their causes, should have resulted in more solar radiation reaching the surface. Surprisingly, the data show that both solar radiation and pan evaporation decreased in most parts of China by 1.9% (3.1 W/m2) and 2.2% (39 mm) per 10-year, respectively. Combined with other evidence revealed in previous studies such as decreased sunshine duration, reduced visibility or clearness, and elevated aerosol optical depth, the principal investigators suggest air pollution produced a foglike haze that reflected and absorbed radiation from the sun and resulted in less solar radiation reaching the surface despite concurrent upward trends in cloud-free skies over China. The data used in this study were obtained from the China Meteorological Administration (CMA) through bilateral agreement of joint research between CMA and the U.S. Department of Energy on global and regional climate change.


Yun Qian, Dale P. Kaiser, L. Ruby Leung, and Ming Xu. 2006. “More frequent cloud-free sky and less surface solar radiation in China from 1955 to 2000” Geophys. Res. Lett. 33, L01812, DOI:10.1029/2005GL024586.