What is Younger Dryas?
The '''Younger Dryas''' (around 12,900 to 11,700 years ago) was a cold period.<ref>{{Cite journal|last1=Rasmussen|first1=S.O.|last2=Andersen|first2=K.K.|last3=Svensson|first3=A.M.|last4=Steffensen|first4=J.P.|last5=Vinther|first5=B.M.|last6=Clausen|first6=H.B.|last7=Siggaard-Andersen|first7=M.L.|last8=Johnsen|first8=S.J.|last9=Larsen|first9=L.B.|last10=Dahl-Jensen|first10=D.|last11=Bigler|first11=M.|date=2006|title=A new Greenland ice core chronology for the last glacial termination|journal=Journal of Geophysical Research|language=en|volume=111|issue=D6|pages=D06102|doi=10.1029/2005JD006079|bibcode=2006JGRD..111.6102R|issn=0148-0227|url=https://epic.awi.de/id/eprint/12532/1/Ras2005a.pdf}}</ref> It reversed the gradual [[climate|climatic]] warming which started around 20,000 years ago. [[File:Evolution of temperature in the Post-Glacial period according to Greenland ice cores (Younger Dryas).jpg|center|500px |Temperatures in the postglacial period, after the [[Last Glacial Maximum]] (LGM). There were very low temperatures for the most part of the Younger Dryas, rapidly rising afterwards to reach the level of the warm [[Holocene]]. This is based on [[Greenland ice cores]].<ref>{{cite journal |last1=Zalloua |first1=Pierre A. |last2=Matisoo-Smith |first2=Elizabeth |title=Mapping Post-Glacial expansions: the peopling of Southwest Asia |journal=Scientific Reports |date= 2017 |volume=7 |pages=40338 |doi=10.1038/srep40338 |pmid=28059138 |language=en |issn=2045-2322|bibcode=2017NatSR...740338P |pmc=5216412 }}</ref>]] At this time there was a sharp fall in [[temperature]] over most of the [[Northern Hemisphere]]. This occurred at the end of the [[Pleistocene]] [[epoch (geology)|epoch]] and just before the present, warmer, [[Holocene]] epoch. The last glacial maximum (LGM) was about 27,000 to 24,000 years ago. The Younger Dryas was the most recent and longest of several interruptions to the gradual warming of the Earth's [[climate]]. The change was relatively sudden, and it resulted in a decline of temperatures in [