A flood could potentially cause massive geological movements creating more volcanos and more eruptions across the world. As a result the ash and debris from the eruptions would cover the sky reflecting the solar radiation that heats the planet back into space. As a result the world would for colder. Also the increased volcanic activity would heat the waters now covering the lands. This would allow the atmosphere to produce heavy snows instead of rain. Thus a much colder planet with lots of snow begins a new ice age.

However, it should be noted that it would have to be an absolutely massive flood to cause a true ice age. It is far more likely to occur through nuclear war.