冰川融化英文ppt.ppt

How do they form? At higher latitudes, the earth doesn’t receive much sunlight and, therefore the temperatures remain low for most part of the year, thus the water can’t remain in liquid form and it solidifies(使凝固) water turns into ice.In case of our own planet: the northern and the southern poles are where the ice caps are located. 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 geological changes The causes for these changes can be explained by Milankovitch Cycles. The cycles proposed by him take into account orbital shapes (eccentricity偏心率), axial tilt轴倾角 (obliquity倾角), axial precession岁差, apsidal precession and orbital inclination倾角. All these factors, when combined, affect the conditions on the planet in the long term and it causes ice ages at different times. During an ice age the ice caps increase in size and they retreat when an ice age ends. These changes occur over a period ranging from thousands to millions of years. seasonal changes They are medium-term changes and they occur every year. Every year with the coming of the winter season, the ice caps begin to expand but they melt again with the coming of the summer seasons. Global Warming There are many causes of the