In the freezing weather, the climbers had to resort to extreme measures to keep warm.

extreme 的意思是"极端的、非常的"，指程度达到极限的。 measures 是名词，意思是"措施、方法"，指为达到某种目的而采取的行动。 extreme measures 指"极端措施"，即非常规的、超出正常范围的应对方法。