While open Arctic waters could be a boon for shipping, fishing and oil exploration, an annual seesawing between ice and no ice could be a particularly harsh jolt to polar bears.

• 虽然北极的开放水域对货运、渔业、石油探勘可以是一项利多，但一年内有冰无冰的拉锯型变化，对北极熊却会是严重的冲击。