The last deglaciation was interrupted by three major cooling events, the Younger Dryas, the Preboreal Oscillation and the 8.2-ka cold event. As the Laurentide Ice Sheet retreated, different outlets from Lake Agassiz became available causing the proglacial lake to drain to a new level in a rather short timescale (flood) and divert continental runoff over hundreds of years (routing). Here we use an Earth System Model to investigate the impact of floods (short term, high amplitude) versus routing events (long term, low amplitude) on the thermohaline circulation and the resulting climate change. We show that the initial outbursts of freshwater are not strong enough to influence large-scale climate and can therefore not be the cause of millennial-scale climate variability. However, routing events have the potential of weakening the thermohaline circulation and therefore causing a cool event in the Northern Hemisphere.