As the earth warms, the melting of the earth’s two massive ice sheets—Antarctica and Greenland—could raise sea level enormously.If the Greenland ice sheet were to melt, it would raise sea level 7 meters (23 feet). Melting of the West Antarctic Ice Sheet would raise sea level 5 meters (16 feet). But even just partial melting of these ice sheets will have a dramatic effect on sea level rise. Senior scientists are noting that the Intergovernmental Panel on Climate Change (IPCC) projections of sea level rise during this century of 18 to 59 centimeters are already obsolete and that a rise of 2 meters during this time is within range.
As I note inPlan B 3.0: Mobilizing to Save Civilization, assessing the prospects for the Greenland ice sheet begins with looking at the warming of the Arctic region. A 2005 study, conducted by the Arctic Climate Impact Assessment (ACIA) team, an international group of 300 scientists, concluded that the Arctic is warming almost twice as fast as the rest of the planet. It found that in the regions surrounding the Arctic, including Alaska, western Canada, and eastern Russia, winter temperatures have already climbed by 3-4 degrees Celsius (4–7 degrees Fahrenheit) over the last half-century.
在美国参议院商务委员会作证时,因纽特人希拉·瓦特-克劳蒂埃代表生活在阿拉斯加、加拿大、格陵兰岛和俄罗斯联邦的15.5万因纽特人发言,她把他们在快速变化的北极气候中挣扎求生描述为“地球正在发生的事情的快照”。她称北极变暖是“这个星球历史上的决定性事件”。
The ACIA report described how the retreat of the sea ice has devastating consequences for polar bears, whose very survival may be at stake. A subsequent report indicated that polar bears, struggling to survive, are turning to cannibalism. Also threatened are ice-dwelling seals, a basic food source for the Inuit.
自2005年的这份报告以来,有新的证据表明,这个问题比以前认为的更严重。来自国家冰雪数据中心和国家大气研究中心的一组科学家得出结论,冰融化的速度比气候模型预测的要快得多。他们发现,从1979年到2006年,夏季海冰收缩速度加快到每十年9.1%。2007年,北极海冰比2005年的记录减少了大约20%。这表明,在2050年之前,海洋可能会无冰,这是IPCC在其2007年报告中预测的最早日期。一些科学家现在认为,到2030年夏天,北冰洋可能会无冰,如果不是更早的话。北极科学家朱利安·施特略夫(Julienne Stroeve)观察到,北极海冰的减少可能已经达到“一个临界点,可能会引发一系列气候变化,影响到地球的温带地区”。
Scientists are concerned that “positive feedback loops” may be starting to kick in. This term refers to a situation where a trend already under way begins to reinforce itself. Two of these potential feedback mechanisms are of particular concern to scientists. The first, in the Arctic, is the albedo effect. When incoming sunlight strikes the ice in the Arctic Ocean, up to 70 percent of it is reflected back into space. Only 30 percent is absorbed as heat. As the Arctic sea ice melts, however, and the incoming sunlight hits the much darker open water, only 6 percent is reflected back into space and 94 percent is converted into heat. This may account for the accelerating shrinkage of the Arctic sea ice and the rising regional temperature that directly affects the Greenland ice sheet.
If all the ice in the Arctic Ocean melts, it will not affect sea level because the ice is already in the water. But it will lead to a much warmer Arctic region as more of the incoming sunlight is absorbed as heat. This is of particular concern because Greenland lies largely within the Arctic Circle. As the Arctic region warms, the island’s ice sheet—up to 1 mile thick in places—is beginning to melt.
The second positive feedback mechanism also has to do with ice melting. As the surface begins to melt, some of the water filters down through cracks in the glacier, lubricating the surface between the glacier and the rock beneath it. This accelerates the glacial flow and the calving of icebergs into the surrounding ocean. The relatively warm water flowing through the glacier also carries surface heat deep inside the ice sheet far faster than would simple conduction.
Several recent studies report that the melting of the Greenland ice sheet is accelerating. A study published inSciencein September 2006 reported that the rate of ice melt on the vast island has tripled over the last several years. In October 2006, a team of NASA scientists reported that the flow of glaciers into the sea was accelerating. Eric Rignot, a glaciologist at NASA’s Jet Propulsion Laboratory, said, “None of this has been predicted by numerical models, and therefore all projections of the contribution of Greenland to sea level [rise] are way below reality.”
At the other end of the earth, the 2-kilometer-thick Antarctic ice sheet, which covers a continent about twice the size of Australia and contains 70 percent of the world’s fresh water, is also beginning to melt. Ice shelves that extend from the continent into the surrounding seas are starting to break up at an alarming pace.
In May 2007, a team of scientists from NASA and the University of Colorado reported satellite data showing widespread snow-melt on the interior of the Antarctic ice sheet over an area the size of California. Konrad Steffen, one of the scientists involved, observed, “Antarctica has shown little to no warming in the recent past with the exception of the Antarctic Peninsula, but now large regions are showing the first signs of the impacts of warming.”
The International Institute for Environment and Development (IIED) has analyzed the effect of a 10-meter rise in sea level, providing a sense of what the melting of the world’s largest ice sheets could mean. The IIED study begins by pointing out that 634 million people live along coasts at or below 10 meters above sea level, in what they call the Low Elevation Coastal Zone. This massive vulnerable group includes one eighth of the world’s urban population.
One of the countries most vulnerable is China, with 144 million potential climate refugees. India and Bangladesh are next, with 63 and 62 million respectively. Viet Nam has 43 million vulnerable people, and Indonesia, 42 million. Others in the top 10 include Japan with 30 million, Egypt with 26 million, and the United States with 23 million.
世界上从未出现过如此大规模的潜在流离失所人口。一些难民可以直接撤退到本国地势较高的地方。另一些人则面临着家乡内陆地区的极度拥挤,他们会在其他地方寻求庇护。孟加拉国已经是世界上人口最密集的国家之一,它将面临更大的人口集中:实际上,它的6200万人将被迫迁入,而9700万人生活在更高的地方。
Not only would some of the world’s largest cities, such as Shanghai, Kolkata, London, and New York, be partly or entirely inundated, but vast areas of productive farmland would also be lost. The rice-growing river deltas and floodplains of Asia would be covered with salt water, depriving Asia of part of its food supply.
In the end, the question is whether governments are strong enough to withstand the political and economic stress of relocating large numbers of people while suffering losses of housing and industrial facilities. The relocation is not only an internal matter, as a large share of the displaced people will want to move to other countries. Can governments withstand these stresses, or will more and more states fail?
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Adapted from Chapter 3, “Rising Temperatures and Rising Seas ,” in Lester R. Brown,Plan B 3.0: Mobilizing to Save Civilization(New York: W.W. Norton & Company, 2008), available for free downloading and purchase atwww.earthpolicy.org/Books/PB3/index.htm.
Image credit:Stig Nygaard at Flickrunder aCreative Commons license
TJJsays
So what year can I take a sail boat across the artic without hitting “any” floating ice? Do not give me any weasle words such as “might” or “could”. Give me a year that you will stake your reputation on.
Maurice Hersonsays
This was the subject of the themed part of our magazine late last year – available free online athttp://www.fmreview.org/climatechange.htm
《强制移民评论31》有38篇文章——没有涉及科学本身,而是涉及气候变化的政策和人道主义后果。
Annasays
I’m researching a story right now on the Newtok community of Alaska and their relocation due to rising river and sea levels. Thanks for this great post!