在夏季，冰会从北极和一些山顶消失，永冻层将会变得“无常”，海平面将继续上涨。

Ice will vanish from Arctic summers and some mountaintops, permafrost will become impermanent, sea levels will keep rising.

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例如平均气温的上升，它会使长期冰藏在冰层里的二氧化碳和甲烷从永冻层里释放出来——相当于温室气体二氧化碳的20倍密度。

Rising average temperatures, for example, threaten to unlock long-frozen stores of carbon dioxide and methane -- at least 20 times as potent a greenhouse gas as CO2 -- from the region's permafrost.

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研究人员通过观测被称为泥炭丘的小丘来测量永冻带边界北退的程度，泥炭丘是在北部泥炭沼泽含冰的土壤上自然形成的。

The researchers measured the retreat of the permafrost border byobserving hummocks known as "palsas, " which form naturally over icecontained in the soil of northern peat bogs.

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