In the past 2m years the temperature has gone up and down like a yo-yo as ice ages have alternated with warmer interglacial periods.

• 在过去20年里，气温起伏就像我们童年玩的溜溜球那样，时高时低，一如地球上寒冷的冰川期和温暖的间冰川期不断地轮换交替。