Recent decades have likely been the wettest on record in the semi-arid Tibetan plateau, researchers say, warning that any further large-scale warming might lead to even greater rainfall in Tibet, the birthplace for Asia's great rivers.
The wettest individual year reconstructed in 3,500 years in northeastern Tibet is 2010, say climate researchers at the University of East Anglia (UEA) and the Chinese Academy of Sciences in an online paper in US academic journal Proceedings of the National Academy of Sciences.
It says precipitation during the past 50 years in the plateau has been historically high. The researchers have reconstructed precipitation records by using sub-fossil, archaeological and living juniper tree samples from the plateau.
They reveal a trend towards wider growth rings on trees, implying moister growing conditions, with the last 50 years seeing increasing amounts of rainfall.
Tim Osborn from UEA's climatic research unit said: "Our collaboration with scientists from China has been very fruitful, leading to what is currently the longest tree-ring-width record in the cold and arid northeastern Tibetan plateau."
"Not only is the record very long, it is based on samples from more than 1,000 trees, some of which have an individual lifespan of more than 2,000 years. These are among the longest-lived trees in the world," he said.
Osborn said these trees are not only long-lived but are useful for understanding how climate has changed.
"The widths of the tree rings show a close correspondence with observations from rain gauges over the last 55 years, such that tree rings in wetter years tend to be wider than tree rings in drier years."
He said the most recent few decades have seen, on an 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.
According to Osborn, over the last 2,000 years when the northern hemisphere was warm, it appeared to be wetter in the mountains of northeastern Tibet. "This suggests that any further large-scale warming might be associated with even greater rainfall in this region - though we note that other factors could also have contributed to the increased ring widths."
The 17th Karmapa Ogyen Trinley Dorje, the third most important Tibetan religious head, also believes Tibet is currently highly vulnerable to climate change.
"It's an unfortunate fact that the temperature of the Tibetan plateau is increasing faster than most other places on earth due to climate change," said the Buddhist monk in a write-up titled "Walking the Path of Environmental: Buddhism through Compassion and Emptiness" in Conservation Biology, a prestigious scientific journal.
The Karmapa, who resides in a monastery on the outskirts of this town from where the Tibetan government-in-exile functions, says Tibet is sometimes called the Third Pole because it stores the most ice and water after the Arctic and Antarctic.
"If its water sources dry up or become contaminated, there will be fateful consequences for over a billion people," he said.
Even a report of Tibetan government-in-exile points out that the Tibetan plateau is staring at ecological destruction.
"Human activities are mainly responsible for the destruction of Tibet's ecological balance," says the report titled "A synthesis of recent science and Tibetan research on climate change".
According to the report, the temperature increase on the Tibetan plateau is twice the global average, resulting in quicker degradation of permafrost, drastic changes in climate patterns and desertification of vast grasslands.
Tibetan spiritual leader Dalai Lama has also expressed concern over the issue.
According to the Dalai Lama's official website, he has expressed concern over deterioration of the environment in Tibet, the rapid disappearance of animal and plant life and the large-scale deforestation and mining activities at the origin of major international rivers.
"Many of the rivers which flow through large areas of Asia, through Pakistan, India, China, Vietnam, Laos and Cambodia, rivers such as the Yellow river, Brahmaputra, Yangtse, Salween and Mekong, all originate in Tibet. It's at the places of origin of these rivers that large-scale deforestation and mining are taking place. The pollution of these rivers has a drastic effect on the downstream countries," the spiritual leader said.
The Dalai Lama, along with many of his supporters, fled Tibet and took refuge in India when Chinese troops moved in and took control of Lhasa in 1959. India is home to around 100,000 Tibetans.
(Vishal Gulati can be contacted at vishal.g@ians.in)
