Scientists warn of an initial period of flooding and of the bursting of glacial lakes that now collect melting water. Too much melt, and the waters burst past unstable walls of rock and silt called moraines - potentially causing mudslides. But once the lakes are emptied, rivers would shrink.
The eastern Himalayas, which sit in the Ganga basin, have the severest melts. Due to unusual monsoon patterns, and possibly to global warming, those glaciers on the "roof of the world" from Bhutan to Kashmir are shrinking fastest. Instead of winter snows that allow glaciers to accumulate bulk, the summer monsoon rains are pelting the glaciers, causing them to melt.
Take the three-mile long Dokriani Barnak glacier, one of the many formed after the Indian subcontinent collided with the Asian landmass 40 million to 50 million years ago. The glacier is one of the most studied in the world. Since 1990 it has receded a half mile. After a numbing sub-arctic winter in 1997, scientists expected Dokriani to expand. Instead, in the summer of 1998, it receded farther.
"That is a phenomenal melt rate," Joseph Gergan of the Wadia Institute of Himalayan Geology told Science magazine. The rate was high again this year.
How much warmer the monsoon rains are as a result of global warming, and how much thicker they fall, is a matter of debate. Scientists disagree over the actual causes of melting glaciers and to what degree the greenhouse gases are responsible.
Since the Little Ice Age" that lasted from 1430 to about 1850, global temperatures have risen. In the past 30 years, the earth's overall average temperature has increased by 5 degrees F., by some estimates. In Bonn this week, the environmental ministers from around the world met to set targets for cutting pollution. Syeda Sajeda Chowdhury, Bangladesh's minister for environment and forests, said that nearly 20 percent of her country could be under water in 15 years if global warming isn't controlled.