BEIJING, April 16 (Xinhua) -- Chinese researchers have discovered that greenhouse gases and anthropogenic aerosols induced rainfall reduction in northern Central Asia.
Central Asia, one of the largest dryland regions in the Northern Hemisphere, is characterized by scarce precipitation and high evaporation.
The reduction of summer rainfall since the 1950s has resulted in severe drought and the degradation of vegetation over northern Central Asia, according to the researchers from the Institute of Atmospheric Physics, Chinese Academy of Sciences.
By evaluating both natural factors including solar activity and volcanic aerosols and external forces including greenhouse gases and anthropogenic aerosols, the researchers showed evidence that the drying trend is dominated by anthropogenic change of the atmospheric circulation evinced in the southward shift and weakening of the subtropical westerly jet.
The subtropical westerly jet is one of the important circulation systems in Eurasia and is closely linked to summer precipitation over northern Central Asia at different time scales.
The observed changes in the subtropical westerly jet are attributable to the combined contributions of greenhouse gases and anthropogenic aerosols, according to the recent research article in the journal Geophysical Research Letters.
Enhanced emissions of greenhouse gases favor an equatorial shift of the subtropical westerly jet, while increased Asian pollution and reduced European aerosol emissions weaken the subtropical westerly jet, said the article.
Both of these factors strengthened the descending motion and decreased the precipitation over northern Central Asia.