A man shields himself from the rain with an umbrella while walking along a promenade in Hong Kong on April 11, 2015. (AFP PHOTO)

A study of past trends in the East Asian summer monsoon rain suggested that the rain belt may move northward due to global warming, reversing the dryness observed during the last few decades in northern China. 

"To put it simply, the drying in northern China over the last decades is transient," lead author Shiling Yang with the Institute of Geology and Geophysics of the Chinese Academy of Sciences, told Xinhua. "Geologic records showed that global warming will surely shift the East Asian summer monsoon rain belt northward, thereby greatly improving the ecological environment in northern China, which would benefit hundreds of millions of people." 

The findings were published Monday in the U.S. journal Proceedings of the National Academy of Sciences. 

The East Asian summer monsoon rain belt has been migrating southward since the 1970s, with more droughts in northern China countered by more floods in southern China. 

Some researchers argued that global warming may explain the southward shift in the monsoon rain belt, which fuelled concerns about the drying problem in northern China, as human activities continue to increasingly emit greenhouse gases into the atmosphere. 

To understand how the monsoon belt may continue to shift with further climate change, Yang and colleagues investigated monsoon rain belt shifts during past episodes of climate change, preserved in organic matter found in loess-soil deposits in China's Loess Plateau. 

The researchers measured carbon isotope ratios for bulk organic matter dating back to the peak of the last Ice Age about 20,000 years ago, which is referred to as the Last Glacial Maximum (LGM), as isotope ratios provided measures of biomass of plants that used the so-called C₄ photosynthetic pathway. 

They found the spatial distribution of C₄ plant biomass is "a robust analog" for the monsoon rain belt, which migrated at least 300 kilometers to the northwest from the cold Last Glacial Maximum to the warm Holocene 4,000 years ago. 

The results strongly support the idea that a warming climate shifts the monsoon rain belt northward, they said. 

"As global warming continues, the current southward displacement of the monsoon rain belt will reverse. Over a longer time scale, the belt will surely move northward, leading to increased precipitation in northern China," Yang said. "The findings provide a scientific basis for the review of the effect of global warming on the climate and the fragile ecology area in northern China." (Xinhua)