polar ice cappolar ice cap meltingeffectscausessolutionsHow do they form?At higher latitudes, the earth doesnt receive much sunlight and, therefore the temperatures remain low for most part of the year, thus the water cant remain in liquid form and it solidifies i.e. turns into ice.In case of our own planet: the northern and the southern poles are where the ice caps are located.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 34 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 km.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 km and contains 25-30 million km of ice. Around 70% of the fresh water on the Earth is held in this ice sheet. The Ice Is MeltingBy BAN KI-MOONPublished: September 17, 2009 New York TimesTwo 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 worlds 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.CAUSESgeological changesseasonal changesglobal warminggeological changesThe 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 changesThey 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 melting of the polar ice caps and global warming, some of which are natural. However, the activities of man are responsible for much of the rapid change that scientists are seeing. Humankind engages in a multitude of activities that have accelerated the process of 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 activity that has accelerated global warming. More people on the planet means there are greater energy requirements, more transportation and increased need for food. Because of the need for cheap goods due to the amount of people on the planet, plastic goods have been constructed, which are not biodegradable. More people also means more cars and more carbon emissions moving into the air. The more people there are, the more room needs to be made for the worlds population, which leads to expansion into wild, natural areas, like forests, which protect the planets delicate balance.One of the least well-known causes of global warming is deforestation. Because of mans craving for space, lumber, and beef, many of the planets forests have been destroyed. Trees have been cut down to be used for construction, in order to clear room for new developments or houses, and to make room for cattle to graze in order to satisfy the demand for beef, especially in the United States. However, the forests around the planet have a protective purpose, because they produce oxygen that reduces the amount of carbon dioxide in the atmosphere. When forests are slashed and burned, carbon emissions skyrocket猛涨. Both the act of burning these organic materials and the loss of the trees speed up global warming.Effects of meltingThe Arctic could see ice-free summers by the end of the 21st century if the current rate of ice cap shrinking continues, according to the Natural Resources Defense Council (NRDC). The largest block of ice in the Arctic is breaking into pieces, and the summer polar ice cap has shrunk some 20 percent since 1979. Melting ice caps affect local residents and wildlife, and could have a far-reaching impact worldwide through rising sea levels and global temperaturesClimateResearch carried out by scientists at NASA美国国家航空航天局 shows that melting ice caps have an effect on the Earths climate. The polar ice caps that cover the top and bottom of the Earth reflect sunlight into space. When the ice caps recede due to melting, the sunlight is absorbed by the ocean and land instead of being reflected back to space. As a result, the planet becomes warmer, more ice melts and the cycle repeats itself. The Environmental Protection Agency (EPA) cites a study on its website produced by the Arctic Council which states that in recent decades the average temperature in the Arctic has risen at nearly double the rate of temperatures elsewhere in the world. This warming is evidenced by melting of glaciers and sea ice, which affects the climate system through such phenomena as increased acidity in the ocean and an uptake in greenhouse gases.OceansThe NRDC美国自然资源保护委员会 notes on its website that the melting Arctic ice caps could have an impact on the Earths sea levels. As ice sheets and glaciers melt, oceans around the world rise. These rising sea levels result in freshwater contamination, flooding and beach erosion. Rising sea levels could have a devastating impact on island nations and citiessuch as the Maldives or Shanghai that are at or near sea level. In the U.S., a 3-foot level sea rise-which could occur by the year 2100-would result in the inundation洪水 of more than 22,000 square miles of land along the Gulf Coast.墨西哥湾岸区EcosystemsThe melting polar ice caps have a wide-ranging impact on ecosystems. Migratory animal species that depend on the Arctic as a place to feed and reproduce are negatively affected by a loss of sea ice. Species that are native to the Arctic, such as polar bears and seals, are particularly hard hit by sea ice reduction.As ice disappears, trees that grow in their place would absorb sunlight and contribute to the warming in the area, according to the EPA环境保护局. People living in the Arctic region may see buildings and workplaces destabilized due to the thawing of frozen ground. Along coastlines, villages are in danger of being flooded.Advices from Ban Ki-moon First, every country must do its utmost to reduce emissions from all major sources. Industrialized countries have to strengthen their mitigation减轻 targets, which are currently nowhere close to what the IPCC政府间气候变化专门委员会 says is needed. Developing countries, too, must slow the rise in their emissions and accelerate green growth as part of their strategies to reduce poverty.Second, a successful deal must help the most vulnerable to adapt to the inevitable impacts of climate change. This is an ethical imperative as well as a smart investment in a more stable, secure world.Third, developing countries need funding and technology so they can move more quickly toward low-emissions growth. A deal must also unlock private investment, including through carbon markets.Fourth, resources must be equitably managed and deployed in a way that all countries have a voice.Advices for individuals There are many simple things you can do in your daily life what you eat, what you drive, how you build your home that can have an effect on your immediate surrounding, and on places as far away as Africa.Here is a list of few things that you can do to make a difference : Adjust Your Thermostatrmstt n.自动调温器自动调温器, 温度调节装置温度调节装置Use Recycled PaperUse Compact Fluorescent flresnt adj. 萤光的 BulbsTake Shorter Showers Install a Low-Flow Showerhead Buy Minimally Packaged GoodsAir Dry Your ClothesBring Cloth Bags to the Market.Extra Effort From Students Recycle Educate Your Parents No Waste at School Meals and Events Plant TreesStart a Club.If everybody make a little change and contribution to prevent global warming, we would be doing a great thing. So please take into consideration what we have discussed, and try to do your part. After all, it will be our next generations that will feel and suffer from the effects.(geophysics) Periodic variations in the earths position relative to the sun as the earth orbits, affecting the distribution of the solar radiation reaching the earth and causing climatic changes that have profound impacts on the abundance and distribution of organisms, best seen in the fossil record of the Quaternary Period (the last 1.6 million years). 米兰科维奇理论即是从全球尺度上研究日射量与地球气候之间关系的天文理论。该理论认为,北半球高纬夏季太阳辐射变化（地球轨道偏心率、黄赤交角及岁差等三要素变化引起的夏季日射量变化）是驱动第四纪冰期旋回的主因。