You might think that 'global warming' means nothing more than a rise in the world's temperature. But rising sea levels caused by it have resulted in the first evacuation (撤离)of an island nation-the citizens of Tuvalu will have to leave their homeland. During the 20th century, sea level rose 8-12 inches. As a result. Tuvalu has experienced lowland flooding of salt water which has polluted the country's drinking water. Paani Laupepa, a Tuvaluan government official, reported to the Earth Policy Institute that the nation suffered an unusually high number of fierce storms in the past ten years. Many scientists connect higher surface water temperatures resulting from global warming to greater and more damaging storms. Laupepa expressed dissatisfaction with the United States for refusing to sign the Kyoto Protocol, an iuternationa] agreement calling for industrialized nations to reduce their greenhouse gas emissions (导致温室效应的气体排放), which are a main cause of global warming. 'By refusing to sign the agreement, the US has effectively taken away the freedom of future generations of Tuvaluans to live where their forefathers have lived for thousands of years,' Laupepa told the BBC. Tuvalu has asked Australia and New Zealand to allow the gradual move of its people to both countries. Tuvalu is not the only country that is vulnerable (易受影响的)to rising sea levels. Maumoon Gayoon, president of the Maldives, told the United Nations that global warming has made his country of 311,000 an 'endangered nation'. The text is mainly about ______.