Ice cores from Greenland show that warming and cooling episodes occurred every several thousand years, superimposed on the slower advances and retreats of the northern ice sheets.

• 采自格陵兰的冰心显示，每隔几千年，地球就会重复一次暖化和冷却的事件，时间刚好和北半球冰原缓慢前进与消退的现象重叠。