20,000 years ago New York City’s Central Park was covered with 15,000 feet of polar ice cap. That is settled science. Whatever forces caused it to melt were not human. Those forces are still at work today.
Scientist still do not have a definitive answer for the cause of the Younger-Dryas desertification of Northern Africa, and the creation of the Sahara desert.
Younger Dryas, cool period between roughly 12,900 and 11,600 years ago that disrupted the prevailing warming trend occurring in the Northern Hemisphere at the end of the Pleistocene Epoch (which lasted from 2.6 million to 11,700 years ago). The Younger Dryas was characterized by cooler average temperatures that returned parts of Europe and North America to ice age conditions. The onset of the Younger Dryas took less than 100 years, and the period persisted for roughly 1,300 years. After the period ended, an interval of rapid warming followed, and average temperatures increased to near present-day levels.
