Survival of Tibetan Glaciers

By Dr. James Hansen

Glaciers on the Tibetan Plateau, sometimes called Earth's "third pole", hold the largest ice mass outside the polar regions. These glaciers act as a water storage tower for South and East Asia, releasing melt water in warm months to the Indus, Ganges, Brahmaputra and other river systems, providing fresh water to more than a billion people. In the dry season glacial melt provides half or more of the water in many rivers.

Figure 1. Five ice cores were extracted from the indicated locationson the Tibetan plateau. The white dashed line is the northerly boundary of the Indian monsoon. (View larger image)

Tibetan glaciers have been melting at an accelerating rate over the past decade. Glacier changes depend on local weather, especially snowfall, so glacier retreat or advance fluctuates with time and place. Thus it is inevitable that some Tibetan glaciers advance over short periods, as has been reported. But overall, Tibetan glaciers are retreating at an alarming rate.

Global warming must be the primary cause of glacier retreat, which is occurring on a global scale, but observed rapid melt rates suggest that other factors may be involved. To investigate the possible role of black soot in causing glacial melt, a team of scientists from Chinese research institutes extracted ice cores from five locations on the Tibetan Plateau (Figure 1).

Black soot, which includes black carbon (BC) and organic carbon (OC), absorbs sunlight and can speed glacial melting if BC reaches values of order 10 ng/g (nanograms per gram) or larger. The ice core data revealed that BC reached values of 20-50 ng/g in the 1950s and 1960s for the four stations that are downwind of European pollution sources. BC and OC amounts decreased strongly in the early 1970s, probably because of clean air regulations in Europe.

However, the ice cores also reveal that in the past decade BC and OC began to increase again.   Continued...

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