托福托福【阶段测试-5】-2017服务一体化阅读生态学 Rising Sea Levels 题目解析【小站备考】

Perhaps the most pervasive climatic effect of global warming is rapid escalation of ice melt. Mount Kilimanjaro in Africa, portions of the South American Andes, and the Himalayas will very likely lose most of their glacial ice within the next two decades, affecting local water resources. Glacial ice continues its retreat in Alaska. NASA scientists determined that Greenland's ice sheet is thinning by about 1 m per year. The additional meltwater, especially from continental ice masses and glaciers, is adding to a rise in sea level worldwide. Satellite remote sensing is monitoring global sea level, sea ice, and continental ice. Worldwide measurements confirm that sea level rose during the last century.

Surrounding the margins of Antarctica, and constituting about 11% of its surface area, are numerous ice shelves, especially where sheltering inlets or bays exist. Covering many thousands of square kilometers, these ice shelves extend over the sea while still attached to continental ice. The loss of these ice shelves does not significantly raise sea level, for they already displace seawater. The concern is for the possible surge of grounded continental ice that the ice shelves hold back from the sea.

Although ice shelves constantly break up to produce icebergs, some large sections have recently broken free. In 1998 an iceberg (150 km by 35 km) broke off the Ronne Ice Shelf, southeast of the Antarctic Peninsula. In March 2000 an iceberg tagged B-15 broke off the Ross Ice Shelf (some 90° longitude west of the Antarctic Peninsula), measuring 300 km by 40 km. Since 1993, six ice shelves have disintegrated in Antarctica. About 8000 km of ice shelf are gone, changing maps, freeing up islands to circumnavigation, and creating thousands of icebergs. The Larsen Ice Shelf, along the east coast of the Antarctic Peninsula, has been retreating slowly for years. Larsen-A suddenly disintegrated in 1995. In only 35 days in early 2002f Larsen-B collapsed into icebergs. This ice loss is likely a result of the 2.5°C temperature increase in the region in the last 50 years. In response to the increasing warmth, the Antarctic Peninsula is sporting new vegetation growth, previously not seen there.

A loss of polar ice mass, augmented by melting of alpine and mountain glaciers (which experienced more than a 30% decrease in overall ice mass during the last century) will affect sea-level rise. The IPCC assessment states that “between one-third to one-half of the existing mountain glacier mass could disappear over the next hundred years.” Also, “there is conclusive evidence for a worldwide recession of mountain glaciers . . . This is among the clearest and best evidence for a change in energy balance at the Earth’s surface since the end of the 19th century.”

Sea-level rise must be expressed as a range of values that are under constant reassessment. The 2001 IPCC forecast for global mean sea-level rise this century, given regional variations, is from 0.11-0.88 m. The median value of 0.48 m is two to four times the rate of previous increase. These increases would continue beyond 2100 even if greenhouse gas concentrations are stabilized.

The Scripps Institute of Oceanography in La Jolla, California, has kept ocean temperature records since 1916. Significant temperature increases are being recorded to depths of more than 300 m as ocean temperature records are set. Even the warming of the ocean itself will contribute about 25% of sea- level rise, simply because of thermal expansion of the water. In addition, any change in ocean temperature has a profound effect on weather and, indirectly, on agriculture and soil moisture. In fact the ocean system appears to have delayed some surface global warming during the past century through absorption of excess atmospheric heat.

A quick survey of world coastlines shows that even a moderate rise could bring changes of unparalleled proportions. At stake are the river deltas, lowland coastal farming valleys, and low-lying mainland areas, all contending with high water, high tides, and higher storm surges. Particularly tragic social and economic consequences will affect small island states—being able to adjust within their present country boundaries, disruption of biological systems, loss of biodiversity, reduction in water resources, among the impacts. There could be both internal and international migration of affected human populations, spread over decades, as people move away from coastal flooding from the sea-level rise.

托福托福【阶段测试-5】-2017服务一体化阅读生态学 Rising Sea Levels 题目解析

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