Read the passage and answer to the questions (1-5): A vast mangrove forest shared by Bangladesh and India that is home to possibly five hundred Bengal tigers is being rapidly destroyed by erosion, rising sea levels and storm surges, according to a study conducted by the ZSI. the Sundarbans took the brunt of cyclone Sidr in 2007, but new satellite studies show that 71% of the forested coastlline is retreating by as much as two hundred metres a yuear. If erosion conttinues at this pace. Already threatened tiger populations living in the forest will be put further at risk pettorelli, said "A continuing rale of retreat would see these parts of the mangrove disappear within fifty years. On the Indian side of the Sundarbans, the island which extends most into the Bay of Bengal has receded by an average of 150 meters a year, with a maximum of just over 200 meters; this would see the disappearance of the island in about twenty years." The causes for increasing coastlme retreat,other than direct anthropogenic once, melude incrcased frequency of storm surges and other extreme natural events, rises in sea-leved and increased salinity which increases the vulnerability of mangroves. Research indicates a rapidly retreating coastline that cannot be accounted for by the regular dynmtes of the sundarbans, Degradation is happening fast, weakening this natural" shield for India and Bangladesh. As human development thrives, and global temperature continues to rise, natural protection from tidal wave and cyelones is being degraded at alarming rates. This will inevitably lead to species loss in this richly is done to stop it. The Sundarbans is acritical tiger habitat to loss the Sundarbans would be to move a step closer to the extinction of tigers.The author suggests that the coastline retreat is resulting from ___.