Gazing down over the world from above in the Middle Ages, in AD 1300 perhaps, one of the heavenly creatures which people thought existed, an angel or a dragon or the swift eagle Garuda might have discerned changes since ancient times: swathes of forest removed; new machines being used, plowing taking place faster over longer stretches of field, trade reviving and extending further. The huge seas bore little traffic as yet, but there were daring Polynesian voyagers, Chinese junks, and Inca rafts in the Pacific, European and Arab traders on the Mediterranean Sea and Indian Ocean, Vikings venturing in the Atlantic to Iceland, Greenland, and far western Vinland, and Maya canoes in the Caribbean and Gulf of Mexico. These were widely separated pioneers on nearly empty waters. But the sky visitor would have observed more people on Earth. Built-up areas were spreading, and with them, clearance, erosion, and advancing desert. The Earth as a whole was, however, full of life in many thriving ecosystems. Parts of the continents were still covered with forests. Those places might have looked wild, but peoples had lived there for centuries or millennia, and had learned to subsist within their local ecosystems. Elsewhere, the rate at which humans were altering the face of the Earth was slow but accelerating. It was not proceeding at a steady pace, but it was faster than it had ever been. Certain societies were learning skills that would in future times become more effective. They were learning to learn about the world—haltingly, with insufficient methods—but learning nonetheless. In the age to come, they would break forth upon the rest of the Earth. Preparations for rapid modern changes were made in the Middle Ages.
The Middle Ages constituted a period in which the relationship of human societies to nature varied greatly in parts of the world distant from one another. The oikoumene, as the Greeks called the inhabited Earth, was not what it was to become, a world united by travel and communication. While civilizations in continental regions were not completely isolated, the degree of contact was much less than it would be in later periods. Patterns of increasing economic activity and growth were sporadically interrupted by stress and decline. At times ecosystems suffered from overuse; at other times they recovered and flourished. Human societies, too, alternately burgeoned and faced disasters against which they often had no effective defenses. They worked with what they had, and demonstrated creativity in ways of dealing with the natural world. Important new discoveries occurred in technology, exploration, education, government, and agriculture. Their success or failure often depended on the degree to which they understood and were able to adapt to ecosystems. For example, during the North Atlantic warm period between 980 and 1,450 settlers from relatively mild Scandinavia lived in Greenland. When the Little Ice Age arrived, climatic stress forced them to abandon their farms and hamlets, while local Inuit communities, with a cultural heritage formed in the Arctic, survived.