The amount of ice on Earth was pivotal in the creation of human civilization ten thousand years ago, a fact that paleo-climatologists only discovered in the late twentieth century.
About 120,000 years ago when modern humans were evolving during the Eemian Period of the middle Paleolithic Age the temperatures on earth allowed for forests to grow above the Arctic circle. Then the temperature dropped quickly and an ice age began. For the next 100,000 years the climate of the planet became less stable and early humans moved from place to place to find temperate weather, as ice and deserts shifted and temperatures moved in wild swings. About 10,000 B.C., the climate stabilized. When it stabilized, the habitable places stayed more or less habitable. A stable climate helped humans stop being nomads. A stable climate allowed for agriculture and people settled, which led to humankind’s first civilizations in places like the Fertile Crescent and Indus Valley.
Mohenjo Daro, Indus Valley: The "great bath" is without doubt the earliest public water tank in the ancient world (National Geographic)
The climate stabilized because there was just the right amount of ice on the planet reflecting sunlight back into space so that it didn’t overheat Earth or its inhabitants. For the past ten thousand years or so, glaciers and ice sheets shrank in summer and grew in winter, but they had a mean or average size that was stable over time. Human civilizations were developing in the "human environmental niche”. During that earlier period 120,000 years ago the average temperatures were apparently around 1 to 2 degrees Celsius warmer than today. The habitable areas of the Earth were very different and sea level was substantially higher inundating large land areas as most of the glaciers and ice sheets receded almost completely. Now those conditions are returning and there is less and less ice.
What’s happening is the end of the earth’s stability. A study of the conditions today published in the Proceedings of the National Academy of Sciences is substantiating the potential outcome of destabilizing of the “human environmental niche”. In human terms, that means that without substantial climate mitigation there will be a return to migration, but in a population of not just a few million, but several billion. More than a third of the 8 billion people on earth today live in areas that will not be habitable in the next 50 years. Areas most affected will include large portions of northern Africa, the Middle East, northern South America, Central America, South Asia, and parts of Australia. Today’s “Refugee Crisis” will pale in comparison to what humanity faces by 2070..
Refugee Camp, UNHCR: 2015
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