Could the Younger Dryas happen again?
NASA: Unlikely. When it occurred previously the world was a very different place with major ice sheets in areas that are now much warmer. The differences in freshwater in the North Atlantic projected for the next 50 to 100 years are much less than the melting that was going on then. However, while this scenario is unlikely, scientists continue to make observations that are relevant to this question and refine the models that are used for climate change scenarios.
NSIDC: Past events, like the Younger Dryas, show that climate can respond in rapid and hard-to-predict ways to slow persistent forcings (a push on the climate system, such as excess heat in the atmosphere or ocean, wind shifts, or density changes in ocean water). One of the major differences between the present-day situation and the past is that the current forcing, greenhouse gases in the atmosphere, is unlike forcings that led to past climate changes (such as changes in Earth’s orbit, or solar influences). Thus, the future course of Earth’s climate is hard to forecast, since no simple analog exists in the recent record of natural climate changes.