冰川周期（glacial cycle）又称冰期旋回（cycle of glacial age）。一个冰川周期，由冰期和间冰期两个互相对立而又互相转化的气候期组成。冰期由初冰期开始，进入最盛的全冰期阶段，然后冰期减弱，向气候增暖的负冰期转化，最后进入湿热的间冰期。
然而，兰皮诺和其他人对传统主义者的一个基本假设提出了质疑：在整个地球历史中，冰川期是周期性发生的。
Yet Rampino and others question one of the traditionalists' basic assumption: the periodic occurrence of glaciation throughout Earth's history.
即使在没有冰川的时期，天文周期也会对地球的气候产生影响。
Astronomical cycles have an effect on Earth's climate even during periods when there is no glaciation.
这一周期约90%的时间为冰川时代，在那期间，我们北半球大部分覆盖着厚达数英里的冰层。
During glacial ages that exist about 90% of the time, our Northern Hemisphere is mostly covered with ice up to several miles thick.
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