The climate of Tibet has been anomalous over the past fifty years, although perhaps not in an expected way: The high plateaus of northeastern Tibet have seen some of their wettest years in several millennia over the past five decades, according to a paper by British and Chinese scientists published online on Feb. 11 in a leading academic journal, Proceedings of the National Academy of Sciences.
Scientists at the University of East Anglia and the Lanzhou (China)-based Cold and Arid Regions Environmental and Engineering Research Institute have produced a detailed chronology of past precipitation patterns by examining tree-ring records dating back 3,500 years. The width of annual tree ring growth and other growth patterns are impacted by yearly rainfall. (Characteristics vary according to tree species; in general, wetter years yield more growth and wider tree rings.)
“The most recent few decades have, on average, the widest rings in the 3,500-year record—which suggests that this may have been the wettest period, perhaps associated with global warming during the last century,” Dr. Tim Osborn, a climate scientists at the University of East Anglia, said in a statement. The team’s research suggests, he said, “that any further large-scale [global] warming might be associated with even greater rainfall in this region.”
As the planet’s temperature warms, weather systems will shift. But scientists don’t agree as to how climate change will recast regional precipitation patterns. In particular, the question of how the Asian monsoon system (subscription required)—which shapes rainfall over a region home to half the world’s population—will evolve has proven tricky to model. While several climate models have predicted that seasonal rains in India will grow more intense, they appear to have weakened in the past few years. Whether these years represent an anomaly, or whether the models need tweaking, remains a hotly debated question.
Meanwhile scientists are constructing detailed chronologies of past rainfall patterns in order to provide some clues about the future. The study of ancient tree rings, known as dendrochronology, allows researchers to gather empirical information about the past—and provides a data set against which to test complex equations modeling how changing climate variables will impact future precipitation, in Tibet and elsewhere.