Then, at about 12,800 years ago, something strange happened. Earth was abruptly plunged back into a deep chill. Temperatures in parts of the Northern Hemisphere plunged to as much as 8 degrees Celsius colder than today. The cold snap lasted only about 1,200 years - a mere blip, in geologic time. Then, just as abruptly, Earth began to warm again. But many of the giant mammals were dying out. And the Clovis people had apparently vanished.
Geologists call this blip of frigid conditions the Younger Dryas, and its cause is a mystery. Most researchers suspect that a large pulse of freshwater from a melting ice sheet and glacial lakes flooded into the ocean, briefly interfering with Earth's heat-transporting ocean currents. However, geologists have not yet found firm evidence of how and where this happened, such as traces of the path that this ancient flood traveled to reach the sea (SN: 12/29/12, p. 11).
Comment: The book Cataclysm!: Compelling Evidence of a Cosmic Catastrophe in 9500 B.C. by Allan and Delair contend that the evidence of a deluge is etched in stone all over the planet however is currently explained away by mainstream science as marks left by 'ice sheets' - which they go on to show probably didn't exist.
Comment: There is actually a wealth of scientific evidence that shows the cause of this sudden shift was due to a cosmically induced catastrophe. Myths all around the world also attest to a global conflagration and deluge. One of the many problems with mainstream science is its myopic view to what was a global and multifaceted event: