Are China's greens set to turn to brown?
China has become greener in recent decades. Since the 1980s trees, shrubs and grasses have been flourishing, thanks to warmer temperatures, a longer growing season and plenty of rain. But now research shows that this beneficial trend appears to be tailing off, with drought stress predominant in some areas. If the warmer, drier trend continues then China's lush green appearance may start turning to parched brown.
Shushi Peng, from Peking University in Beijing, and colleagues, used satellite-derived Normalized Difference Vegetation Index (NDVI) data to monitor vegetation growth across China between 1982 and 2010. Previous research had shown a major greening trend (over 5% more vegetation growth) across most areas of China between 1982 and 1999.
However, the most recent decade told a different story, with vegetation growth tailing off in most places and coming to a complete halt across much of northern China (Inner Mongolia and the Tibetan Plateau).
"Much of northern China is covered with grassland and alpine vegetation, which are strongly sensitive to climate change and less resilient to climate change than forests," said Peng.
Climate data indicate that the green flush experienced by northern China in the 1980s and early 1990s was due to warmer temperatures, increased rainfall and a longer growing season, in particular the earlier onset of spring. But a continuing increase in temperatures and a decrease in rainfall since the mid-1990s has slowed growth to near zero over the last decade.
Meanwhile, the data of Peng and his colleagues show that the forest-type vegetation found across much of southern China has continued to flourish and grow faster. Their findings are published in Environmental Research Letters (ERL).
These growth trends have important economic and political implications. "The increased vegetation growth in forests in southern China may indicate increasing timber production in plantations, while the reversed growth trend in northern grasslands may reduce their capacity to feed livestock," explains Peng.
And in terms of global climate change, these variations may be altering the capacity of the Earth's "lungs". Currently, vegetation across the world absorbs about one third of the carbon dioxide produced by anthropogenic fossil-fuel emissions. "Even a small change in vegetation photosynthesis could have a large effect on the role of vegetation as a carbon sink," said Peng. "Monitoring the vegetation growth changes is helpful for understanding land carbon sinks and biogeochemical feedbacks for global warming."
Climate models produced by the Intergovernmental Panel on Climate Change predict that temperatures will increase between 1 and 5 °C in China over the coming decades. Meanwhile, rainfall predictions are highly uncertain, ranging from a decrease of 6 mm to an increase of 180 mm. Given the right combination of factors, vegetation growth across China may continue apace. But if dryness starts to dominate then growth is likely to shrink, and China could go from green to brown.
About the author
Kate Ravilious is a contributing editor for environmentalresearchweb.