Around 1250 A.D., historical records show, ice packs began showing up farther south in the North Atlantic. Glaciers also began expanding on Greenland, soon to threaten Norse settlements on the island. From 1275 to 1300 A.D., glaciers began expanding more broadly, according to radiocarbon dating of plants killed by the glacier growth. The period known today as the Little Ice Age was just starting to poke through. Summers began cooling in Northern Europe after 1300 A.D., negatively impacting growing seasons, as reflected in the Great Famine of 1315 to 1317. Expanding glaciers and ice cover spreading across Greenland began driving...