为自己生存的地球做一些贡献

根据美国太空总署（NASA）最新的卫星探测资料， 今年夏末北极的海冰量只有4年前的一半，北极的融冰速 度让科学家担心，全球暖化是不是已经来到临界点。 　　美国华盛顿大学大气科学家毕兹和国家大气研究中心 的荷兰德去年才提出报告预测，全球暖化持续下去，到了 2040年夏天，北极冰层将融化殆尽。本周新提出的报告， 将这种情况出现时间的预测大大提前到2012年。NASA气 候学家兹瓦利说，检视最新资料后，"以这种速度，到了 2012年夏末，北冰洋将几乎完全无冰，比之前预期的速度 快得多。" 　 北极向来被视为气候暖化"矿场里的金丝雀"，作为暖 化的预警讯息，北极地区的状况预言了世界各地其他地区接 下来会出现的情形。许多科学家都对今年融冰情况大感惊讶， NASA低温层科学部门负责人阿布达拉提说："我通常不会太 注意单一的一年…但是今年的变化太大了，特别是北极海冰， 让你不得不注意发生了什麽事？"他说，"这肯定是分水岭的一 年。" 　　今年夏天，格陵兰冰层融化了5520亿吨，比历年夏天平均 融冰量还多15%，并比破纪录的2005年还多了190亿吨﹔今年 格陵兰岛周边海冰减少程度比15年前多四倍，比2005年最糟糕 的那年还多12%﹔格陵兰的冰层占全球总量的1/12，全部融化 的话，全球海平面估计将上升6.7公尺。 　　北冰洋今年夏天海冰数量也比之前的纪录少23%，加上 NASA即将公布的资料显示，海冰不只减少也变薄，变得更容易 融化，科学家也据此估算，今年北极海冰量只有2004年的一半。 　　海冰融解和格陵兰冰层融化引起的连锁效应还包括，海冰会 反射80%的太阳热能，海冰消失，90%来自太阳的热能进入海洋， 温暖的海水加速冰层融化，形成恶性循环，兹瓦利说﹔"情况正变 得比电脑模式预期的还要糟。" 　　本周四将在旧金山召开的美国地球物理学会议上，有全球暖 化教父之称的NASA首席气候学家韩森将宣告，根据格陵兰岛融 冰情况，地球已经达到所谓的全球暖化"引爆点"，他透过电子邮 件接受访问说，"我们还没到无法挽回的地步，还能及时回头， 但是需要迅速的大转弯。"

请多走路，少开车；少吃肉；少消费，您将为自己生存的地球做一些贡献。

Arctic ice melt

Ominous Arctic ice melt worries experts

Updated Tue. Dec. 11 2007 5:48 PM ET

The Associated Press

WASHINGTON -- An already relentless melting of the Arctic greatly accelerated this summer, a warning sign that some scientists worry could mean global warming has passed an ominous tipping point. One even speculated that summer sea ice would be gone in five years.

Greenland's ice sheet melted more than 17 billion tonnes more than the previous high mark, and the volume of Arctic sea ice at summer's end was half what it was just four years earlier, according to new NASA satellite data obtained by The Associated Press.

"The Arctic is screaming,'' said Mark Serreze, senior scientist at the government's snow and ice data centre in Boulder, Colo.

Just last year, two top scientists surprised their colleagues by projecting that the Arctic sea ice was melting so rapidly that it could disappear entirely by the summer of 2040.

This week, after reviewing his own new data, NASA climate scientist Jay Zwally said: "At this rate, the Arctic Ocean could be nearly ice-free at the end of summer by 2012, much faster than previous predictions.''

So scientists in recent days have been asking themselves these questions: Was the record melt seen all over the Arctic in 2007 a blip amid relentless and steady warming? Or has everything sped up to a new climate cycle that goes beyond the worst case scenarios presented by computer models?

"The Arctic is often cited as the canary in the coal mine for climate warming,'' said Zwally, who as a teenager hauled coal. "Now as a sign of climate warming, the canary has died. It is time to start getting out of the coal mines.''

It is the burning of coal, oil and other fossil fuels that produces carbon dioxide and other greenhouse gases, responsible for man-made global warming. For the past several days, government diplomats have been debating in Bali, Indonesia, the outlines of a new climate treaty calling for tougher limits on these gases.

What happens in the Arctic has implications for the rest of the world. Faster melting there means eventual sea level rise and more immediate changes in winter weather because of less sea ice.

In the United States, a weakened Arctic blast moving south to collide with moist air from the Gulf of Mexico can mean less rain and snow in some areas, including the drought-stricken Southeast, said Michael MacCracken, a former federal climate scientist who now heads the nonprofit Climate Institute. Some regions, like Colorado, would likely get extra rain or snow.

More than 18 scientists told The AP that they were surprised by the level of ice melt this year.

"I don't pay much attention to one year ... but this year the change is so big, particularly in the Arctic sea ice, that you've got to stop and say, 'What is going on here?' You can't look away from what's happening here,'' said Waleed Abdalati, NASA's chief of cyrospheric sciences. "This is going to be a watershed year.''

2007 shattered records for Arctic melt in the following ways:

• 500 billion tonnes of ice melted this summer from the Greenland ice sheet, according to preliminary satellite data to be released by NASA Wednesday. That's 15 per cent more than the annual average summer melt, beating 2005's record.
• A record amount of surface ice was lost over Greenland this year, 12 per cent more than the previous worst year, 2005, according to data the University of Colorado released Monday. That's nearly quadruple the amount that melted just 15 years ago. It's an amount of water that could cover Washington, D.C., a kilometre deep, researchers calculated.
• The surface area of summer sea ice floating in the Arctic Ocean this summer was nearly 23 per cent below the previous record. The dwindling sea ice already has affected wildlife, with 6,000 walruses coming ashore in northwest Alaska in October for the first time in recorded history. Another first: the Northwest Passage was open to navigation.
• Still to be released is NASA data showing the remaining Arctic sea ice to be unusually thin, another record. That makes it more likely to melt in future summers. Combining the shrinking area covered by sea ice with the new thinness of the remaining ice, scientists calculate that the overall volume of ice is half of 2004's total.
• Alaska's frozen permafrost is warming, not quite thawing yet. But temperature measurements 20 metres deep in the frozen soil rose more than 0.2 degree Celsius from 2006 to 2007, according to measurements from the University of Alaska. While that may not sound like much, "it's very significant,'' said University of Alaska professor Vladimir Romanovsky.

Greenland, in particular, is a significant bellwether. Most of its surface is covered by ice. If it completely melted -- something key scientists think would likely take centuries, not decades -- it could add nearly seven metres to the world's sea level.

However, for nearly the past 30 years, the data pattern of its ice sheet melt has zigzagged. A bad year, like 2005, would be followed by a couple of lesser years.

According to that pattern, 2007 shouldn't have been a major melt year, but it was, said Konrad Steffen, of the University of Colorado, which gathered the latest data.

"I'm quite concerned,'' he said. "Now I look at 2008. Will it be even warmer than the past year?''