You got me wondering because it is not just seltzer water. That is true with my Pepsi too!

So I looked it up....

Warm sodas fizz more than cold sodas when you open them because CO2 gas is less soluble at higher temperatures. Opening a bottle of soda decreases the pressure inside the bottle. This decreases the solubility of CO2 in the soda and results in the formation of bubbles, or fizz.

So there! (Not entirely sure what all that means.... )