After 1250, glaciers began to expand in Greenland, affecting its thermohaline circulation, and cooling the entire North Atlantic. In the 14th century, the growing season in Europe became unreliable; meanwhile in China the cultivation of oranges was driven southward by colder temperatures. Especially in Europe, the Little Ice Age had great cultural ramifications. It persisted until the Industrial Revolution, long after the Post-classical Period. Its causes are unclear: possible explanations include sunspots, orbital cycles of the Earth, volcanic activity, ocean circulation, and man-made population decline.