Did a Comet Cause the Younger Dryas Cooling?

In a paper to be published in the Monthly Notices of the Royal Astronomical Society, available online now here, astrobiologist Professor Napier of Cardiff University (UK) has announced that he believes that the cooling period in the Upper Paleolithic period known as the Younger Dryas, may have been set off by the impact of debris from a comet. This period of time, almost 13,000 years ago, was responsible for “intense wildfires over North America, major disruption of human culture, and the rapid extinction of 35 genera of North American mammals.”