That too has happened before. We, man, seem to get in an uproar over the extinction of species... but that's a constant occurance. Yes it's a shame if we are the sole cause... but it is a fact of life (literally) on this planet.

Species come and species go. The freshwater will only impact the ocean surfaces and probably only near the poles. Most of it will evaporate into the atmosphere and become distributed around the globe as precipitation. So there will be some species "making" adjustments or dieing off... but others will emerge from new opportunities the changed environment will bring.

We just get very centric about it... as if the whole world revolves around our needs.