The vast majority of abrupt climate changes were preceded by millenial trends. This is exactly true of the Younger Dryas. The Earth was warming for thousands of years before the YD cooling event, which was initiated quickly by the thermohaline circulation cessation. The reason that the YD termination happened so quickly was that all of the other global factors (including, yes, rising atmospheric CO2) set up an even larger warming spike when the THC restarted.
I disagree - the gyrations over the last 2000 years have been of durations from two to three hundred to as short as 40 years (Dalton minimum). You may not see the temp changes of the Dalton Minimum as all that significant, but since we teter on the edge of glaciation, that minor change had serious impacts on those who lived through it (or died as a result).