probably a change in the strength of north atlantic thermohaline circulation.
that was a regional shift in local climate and not due to worldwide climate change. it isn't reflected in global proxies like antarctic ice cores.
hurricane activity in the atlantic basin increased, and its likely that la nina (cool) conditions persisted across the pacific.
it also may have caused draught that caused the collapse of the Maya civilization.
you probably get labelled a shill because you use it to cast doubt on anthropogenic causes of climate change and you argue that warmer temperatures benefited northern europe, while ignoring the drought and destruction of a civilization in central america.