But that is nothing to celebrate, because melting permafrost will release billions of tonnes of methane, an especially potent greenhouse gas.

但是这没有什么值得庆祝的，因为冻土融化将释放几十亿吨的甲烷，温室气体的重要组成部分。

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In the large image, the area behind the shoreline is pockmarked by marshes, ponds, and hummocks characteristic of "thermokarst," landscapes created by the melting and refreezing of permafrost.

在大图中，海岸线后面的区域由湿地、池塘、热融冰丘形成了凹陷，融化的以及重新冻结的冻土层形成了这种景观。

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Even the new figure could be an under-estimate, the team suggests, because it doesn't account for the full range of positive feedbacks, such as melting permafrost releasing methane and carbon dioxide.

研究小组指出，就连这个数字也可能估计不足，因为它没有解释正反馈的方方面面，比如释放出甲烷和二氧化碳正在融化的永久冻土层。

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Mr Smith, the engineer, warns that melting permafrost a mix of frozen mud and water that underlies much of the state will force the replacement of buildings and roads.

ECONOMIST: The state is getting warmer and no one's happy

We saw and heard about the impacts, from slumping land due to the melting of permafrost to hunter stories about the northward migration of species and the challenge that early ice break up poses for transportation.

CNN: Sailing the Northwest Passage: mission accomplished

For things that clearly do have the springlike quality of shifting irreversibly if pulled (or pushed) too far, like the collapse of ice sheets or the melting of permafrost, a boundary system that seeks to stop you getting too close to the threshold seems as sensible as a safety rail is on a parapet.

ECONOMIST: The global environment