I should have included above, but the wikipedia section on global effects shows how it varied by continent. Massive effects in Europe and South America, but with some evidence the Pacific wasn't as affected.
en.m.wikipedia.org/wiki/Younger_Dryas
The earlier intro section there lays out the discovery and some types of evidence that led to the conclusion, and a theory based on geology from China that these rapid changes tend to accompany deglaciation.
20 degrees Fahrenheit shift within a decade, even if just for one continent... It's hard to fathom.
It seems possible that that local climate can change a lot more wildly then the global averages.