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Background: Climate & Evolution

Climate Chaos in Tibet

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NASA satellite image of large glacial lakes forming from ice in the Bhutan Himalayas

The Tibetan plateau is the highest and largest in the world. It is guarded to the south by the Himalayas, to the north by the Kunlun and to the west by the Hindu Kush and Pamir mountain ranges. It contains 46,000 glaciers at an average height of 13,000 feet above sea level. This is the Earth's largest ice mass outside the poles, its Third Pole, sometimes also referred to as the "water-tower of Asia". Direct photographic comparisons made over the last eight decades provide irrefutable evidence of the rate and extent of de-glaciation caused by climate warming in the world's highest mountains. 

The winter accumulation of snow on high mountains is compressed to form ice caps and glaciers.  In summer these glaciers melt slowly, constantly feeding the rivers below.  They are ‘reservoirs in the sky’ [1], present since long before humans practiced agriculture. From India or China to California, the world’s food supply is critically dependent on their melt water.  Many of Asia’s greatest rivers—the Indus, Ganges, Brahmaputra, Salween, Mekong, Yangtze and Huang He—derive their stable year-round flow from the melt water of Tibet's glaciers.   

By 2006, a third of the climate observation stations in Tibet were reporting all-time high temperatures. The average temperature has been rising 6-7 times as fast as in China proper. Aerial surveys over the last 30 years show that snow lines are rising, wetlands are shrinking, and desertification is increasing across the country.

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 The great lake Tso Ngonpo (Qinghai Hu) seen from space

Tibet has always had thousands of lakes, most without an outlet, and dependent on undergound sources. A large number of them have simply disappeared. The water level of the great lake Tso Ngonpo (Ch: Qinghai Hu), for example, fell by 3.6 metres between 1959 and 2005, while its surface area decreased from 4548 to 4206 square kilometres. The decline has produced degradation of grasslands and desertification in its watershed area.

Wetlands on the Tibetan plateau have shrunk about 10% over the past 40 years. Desertification is a major issue especially in the north-east, the source region of the Yellow and Yangtze rivers. Wetlands at the source of the Yangtze river have contracted almost 30%: the area of grassland degradation and soil erosion here reaches over 100,000 square kilometres. The Yangtze provides water for hundreds of millions of people along its route to the sea. In 2006, the water level of its upper reaches sank to its lowest level for 80 years.

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False-colour satellite image of Gangotri Glacier’s retreat (www.globalwarmingart.com)

As the Himalayan glaciers retreat, the volume of water in rivers downstream first increases, causing widespread flooding, and then declines radically. The 30-kilometer long Gangotri is one of the largest glaciers in the Himalayas and feeds into the Ganges River basin. It provides 70% of summer flow in the Ganges, a sacred river for 800 million Hindus. Gangotri is shrinking twice as fast as it was 20 years ago. Here, as elsewhere in India and China, our present trajectory of carbon gas and particulate emissions (so-called "business as usual") will generate  catastrophic water shortages for hundreds of millions of people by mid-century.  

An early symptom of shrinkage and melting of glaciers is the formation of dangerously unstable freshwater lakes behind broken rock moraines, where once there was ice (blue areas below in satellite image below). At first downstream flooding increases.  This is followed by an irreversible decline in river flow, with dramatically negative impacts on drinking water and irrigation. 



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