 Global warming has caused the rivers that pour down from the Himalayas and empty into the Bay of Bengal to swell and shift in recent decades, placing these islands, known as the Sundarbans, in danger.Four islands are completely underwater, and another 10 in the area are at risk.A 2007 study by Jadavpur University concluded that roughly of the Sundarbans had disappeared during the preceding 30 years, and that Ghoramara had shrunk to less than , about half its size in 1969