A large part of the West Antarctic ice sheet appears to be in an “unstoppable” decline meaning global sea level rise predictions will have to be revised, scientists have found.

科学家发现，南极西部冰盖(WAIS)中有一大部分似乎正以一种“无法阻止”的趋势减少，这意味着对全球海平面上升的预测必须加以调整。

Glaciers in the Amundsen Sea that contain enough ice to raise sea levels by four feet (1.2 metres) are thawing faster than expected and there is nothing to stop them melting into the ocean, according to a study based on 40 years of observations by researchers from the Nasa space agency and the University of California, Irvine.

一项研究表明，阿蒙森海的冰川正在以高于预期的速度融化，目前已无法阻止这些冰川融入大洋。这些冰川包含的冰块融化后足以令全球海平面上升4英尺（合1.2米）。这项研究成果是根据美国国家航空航天局(NASA)太空总署及美国加州大学欧文分校(UCI)研究人员40年的观测结果得出的。

“The collapse of this sector of West Antarctica appears to be unstoppable,” said glaciologist Eric Rignot, lead author of the study. “It’s passed the point of no return.”

该研究报告第一作者、冰川学家埃里克•瑞格诺特(Eric Rignot)表示：“南极西部这部分区域的融化似乎已无法阻止，融化进程已超过了能够逆转的临界点。”

The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers, he said. The changes were thought to be linked to climate change.

他表示，这一融化过程在一大片区域同时发生，表明这一融化过程是由一种十分普遍的原因造成的——比如冰川漂浮区域下方海洋热量的增加。有人认为这种变化与全球变暖有关。

Some scientists have previously warned that increased concentrations of man-made greenhouse gases in the atmosphere may be affecting wind patterns around Antarctica and causing other changes that are pushing warmer waters towards the continent.

部分科学家此前曾警告说，大气中人造温室气体含量的增加可能会影响南极洲周围全球季风的分布，从而引发其他方面的变化，将更温暖的海水推向这片大陆。

It could take several centuries for all the ice to flow into the sea, Professor Rignot said, adding that the sector would be a “major contributor to sea level rise in the decades and centuries to come”.

瑞格诺特教授表示，所有冰块全部流入海洋可能要花费几百年时间，他补充说该区域“在今后几十年到几百年里可能会成为海平面上升的主要元凶”。

Projections of global sea levels, which have already risen by nearly 20cm since 1900, will have to be revised as a result of the study’s findings, he said.

他表示，这一研究成果令人们对全球海平面高度的预测不得不加以调整——自1900年以来全球海平面已经上升了近20厘米。

The glaciers studied by the researchers flow out from land to the ocean, where their leading edges float on the seawater. The point on a glacier where it first loses contact with land is called the grounding line.

这些研究人员所研究的冰山前沿漂浮在海水之上，冰川的主体则正在由陆地漂入海洋。在冰川上，接地部分与浮在水面上部分的分界线被称为接地线。

The Antarctic glaciers have thinned so much they are floating above places where they used to sit solidly on land, meaning their grounding lines are retreating inland.

目前，南极洲冰川的厚度已大大减少，以至于在过去原本坚实坐落在陆地上的许多地区，这些冰川已经处于漂浮状态，也就是说这些冰川的接地线正在向内陆收缩。

As glaciers flow faster, they stretch out and get thinner which makes them lighter and lifts them further off the bedrock. As the grounding line retreats and more of the glacier becomes waterborne, it means there is less resistance below and the flow of ice accelerates.

随着冰川漂移速度的加快，它们会四处扩散，其厚度会进一步降低，这使得它们的重量也进一步降低，从而进一步上浮离开岩床。随着接地线的收缩，更多冰川会漂在水上，这意味着冰川底部的阻力会进一步降低，冰块的漂移将会加速。

In order to stop or slow this process, there needs to be hills or bumps coming up from the glacier bed that can snag the ice from below, but the researchers found there are no such “pinning points” upstream from the present grounding lines in five of the six glaciers in the region.

要想阻止或减缓这一进程，冰川底部的岩床上需要出现小山或者丘陵地形，这种地形能够从下部迟滞冰块的漂移。然而研究人员发现，该地区六大冰川中有五块自目前的接地线以外不存在这种“钉子”般的地形。

Only the Haynes Glacier has major obstructions upstream, but it only drains a small section and is retreating as fast as the other glaciers.

只有海恩斯冰川(Haynes Glacier)在漂移路线上存在大型障碍，不过该障碍只会迟滞一小片区域，而该冰川接地线收缩的速度与其他冰川一样快。

The new study is to be published in the Geophysical Research Letters journal.

这一新的研究成果即将发表在《地球物理研究快报》(Geophysical Research Letters)。