The Greenland Ice Sheet is melting -- and that could spell trouble for the northeast coast of the United States and eastern Canada.

Sea level in those regions might rise by as much as a foot more than current projections, according to a new study. Possible consequences include flooding and damage to both cities and ecosystems.

While experts say it's too soon to know how big the effects will be, lead researcher Aixue Hu said it's probably worth bracing for the worst-case scenario.

"In some sense, I think we should be alarmed and prepared that something could happen in the future," said Hu, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo. "Right now, we're not sure which scenario is going to happen. Hopefully, the worst case will not happen."

The Greenland Ice Sheet, a large mass of ice that covers most of Greenland, has been melting at an increasing rate since the early 1990s. In recent years, melting has accelerated at a rate of 7 percent each year. Scientists estimate that the ice sheet won’t disappear completely for another 3,000 years, but effects of melting could happen far sooner than that.

Every drop of water that melts from the ice flows into the ocean, raising sea levels. The input of relatively light freshwater also alters circulation patterns that cycle water between Greenland and northern North America, which could lead to more water on the North American end.

Without factoring in the melting of Greenland ice, warmer surface waters are already expected to shift currents, sending about 8 inches of water above the average global rise to the Northeast by 2100, Hu said.

To find out what melting in Greenland would add to the equation, he and colleagues used a computer model to consider three scenarios, in which melting increased at a rate of 7 percent, 3 percent, or 1 percent each year. The team projected out to the year 2100.

Given the best-case scenario, the researchers report today in the journal Geophysical Research Letters, the east coasts of Canada and New England would get another four inches of water. In the worst-case scenario, sea level would rise by an extra foot in coastal areas from New York to Halifax.

"In the East Coast region, there are many big cities," Hu said. "If sea levels rise, it means some parts of land will submerge under water."

Water could surge over levies and flood estuaries, where organisms depend on a careful balance between salt and freshwater.

Other researchers warn against jumping to conclusions. For now, Greenland's melting contributes less than half a millimeter of water to the oceans each year, said Mike Winton, an oceanographer at the Geophysical Fluid Dynamics Laboratory in Princeton, N.J. That's a tiny amount.

Whether acceleration of melting from the Greenland Ice Sheet will continue, he added, is a big question mark. The Arctic has experienced wide swings in climate variability.

"I don't think we need to get particularly alarmed about this particular phenomenon," Winton said. "It's just part of the mix."

More important will be figuring out how sea level rise is going to vary from one region to the next around the world -- and what we're going to do about it, said glaciologist Eric Rignot.

It can take 30 or 40 years for polar ice to respond to our efforts to reduce emissions of carbon dioxide and other greenhouse gases, said Rignot, of the Jet Propulsion Laboratory in Pasadena, Calif. That means we need to start thinking about the distant future today.

"Even the most conservative people agree that Greenland is doomed," Rignot said. "Sea level is not going to stop rising after 2100. Instead of being scared, we need to take it seriously and plan ahead."
 

2009年5月29日——格林兰冰盖正在消融。这可能给美国东北部和加拿大东部的海岸带来威胁。

一项最新的研究显示，这些区域的海平面可能上升1英尺，将超过目前的预测高度。也许因此引发洪水、城市和生态系统遭受破坏等后果。

虽然专家指出，现在要明确冰盖融化会产生多大影响还为时过早，但是首席研究员胡爱学（音译）说，也许现在就为最坏的情况做好准备是值得的。

胡爱学是美国科罗拉多州博尔德市“国家大气研究中心”的气候学家，他说：“从某种意义上讲，我认为我们应该在担心未来的同时，做好应对的准备。现在，我们还不能肯定将会发生哪些情况。希望不要出现最坏的事。”

从二十世纪90年代起，覆盖格林兰岛大部分区域的格林兰冰盖以越来越快的速度融化。近年来的融化速度每年递增7%。科学家预测要再过3000年，冰盖才会完全消失。但是，冰层融化产生的后果可能要来得早。

冰层融化成的每一滴水汇入海洋后，抬高了海平面。体积相对轻的淡水流入海洋后，还会改变格林兰岛和北美洲北部之间的洋流循环模式，这种情况最终可能导致更多的海水淹没北美大陆。

胡先生表示，正在融化的格林兰冰盖彻底消失之前，估计温暖的表层水已经改变了洋流的流向。到2010年的时候，高出全球平均海平面约8英寸（20.32厘米）的海水将倒灌进美国东北部地区。

为了查明格林兰冰层融化的同时会带来什么，他和同事们利用计算机模型来判断当冰层的融化速度每年递增7%、3%或1%时会发生的3种情形。研究小组一直预测到2100年的情形。

今天《地球物理研究快报》杂志刊登的这篇研究报告得出到的最好情形是，加拿大以及新英格兰的东部沿海将抬高4英寸（10.16厘米）；而最坏的情形是，从纽约到哈利法克斯沿海地区的海平面将升高1英尺（30.48厘米）。

胡先生说：“东部沿海地区有许多大城市。一旦海平面升高，意味着一部分陆地将淹没在水下。”

汹涌的海水可能会漫过堤岸（原文levies 似有误，估计是levees）和泄洪河口，那里的海水和淡水间保持着细微的平衡，是有机生物体赖以生存之处。

而其他的一些研究人员则提出不要过早下结论。新泽西州普林斯顿大学“地球物理流体动力学实验室”的海洋科学家迈克·温顿认为，目前格林兰冰盖每年融化后流入海洋的水量还不到50毫米。那只是很少的水量。

他补充道，格林兰冰盖是否会继续加速融化还是一个大问号。北极曾有过大幅波动的气候多样性。

温顿说：“我认为，我们无需对这种特殊现象过于担忧。这只是北极多变性气候的一部分。”

加州帕萨迪纳“喷气推进实验室”的冰河学家埃里克·里格诺特表示，更重要的是要查明全球各处海平面的上升如何因区域不同而变化，同时要清楚我们该为此做什么。

里格诺特表示，我们努力减少二氧化碳和温室气体排放，但这些行为对极地冰川的影响要过30到40年后才有所显现。这意味着我们现在就要开始考虑遥远未来的事。

里格诺特说：“即使是最保守的人也同意格林兰冰盖注定要消失。2100年以后，海平面的升高也不会停止。不过我们需要的不是恐惧，而是认真对待，防患未然。”