Does global warming affect tsunamis?
Pretty confident to answer No here.

Tsunamis are caused by water displacement due to earthquakes; this has nothing to do with global warming.  Any changes in density would be trivial, and although the water would have more thermal energy, this would not affect or be influenced by the kinetic energy of the Tsunami.

The only way in which a tsunami would be made more severe would be that any sea level rise due to global warming would be added to the Tsunami height.