两极冰川融化 英文.ppt

polar ice cap melting;;How do they form?;Earths north pole is covered by floating pack ice (sea ice) over the Arctic Ocean. Portions of the ice that dont melt seasonally can get very thick, up to 3–4 meters thick over large areas, with ridges up to 20 meters thick. One-year ice is usually about a meter thick. The area covered by sea ice ranges between 9 and 12 million km2. The land mass of the Earths south pole, in Antarctica, is covered by the Antarctic ice sheet. It covers an area of about 14.6million km2 and contains 25-30 million km3 of ice. Around 70% of the fresh water on the Earth is held in this ice sheet. ;The Ice Is Melting By BAN KI-MOON Published: September 17, 2009 New York Times Two weeks ago, I visited the Arctic. I saw the remains of a glacier that just a few years ago was a majestic(宏伟的) mass of ice. It had collapsed. Not slowly melted — collapsed. I traveled nine hours by ship from the world’s northernmost settlement to reach the polar ice rim. In just a few years, the same ship may be able to sail unimpeded（畅通无阻的） all the way to the North Pole. The Arctic could be virtually ice-free by 2030.;I was alarmed by the rapid pace of change there. Worse still, changes in the Arctic are now accelerating global warming. Thawing permafrost is releasing methane, a greenhouse gas 20 times more powerful than carbon dioxide. Melting ice in Greenland threatens to raise sea levels. ;CAUSES;geological changes;seasonal changes;Global Warming;Most people know that the man-made activity that has been cited as a major accelerator of global warming is the combustion of fossil fuels, such as coal and petroleum. Industrial processes and the operation of personal motor vehicles all release various emissions into the air, including carbon monoxide一氧化碳, hydrocarbons碳氢化合物, and lead铅, which turn to carbon dioxide. Mining activities also release methane甲烷 into the atmosphere, which is a greenhouse gas that leads to a warming planet.;The overpopulation of the planet is another