I believe this period is known as the Older Dryas.
The Oldest Dryas was about 18,000 ya, IIRC.
The Younger Dryas was dated about 13,000 - 11,500 ya and de4scribed in Wikipedia as follows:
The prevailing theory holds that the Younger Dryas was caused by a significant reduction or shutdown of the North Atlantic thermohaline circulation in response to a sudden influx of fresh water from Lake Agassiz and deglaciation in North America. The global climate would then have become locked into the new state until freezing removed the fresh water "lid" from the north Atlantic Ocean. This theory does not explain why South America cooled first.
The event described in the article was 8,200 ya but seems to have about the same cause as the Younger Dryas. It would seem that this might be a recurring type of event happening as the glacial ice sheets retreat.