If you had ever listened to people that are trying to help us transition from fossils you would have heard them say consistently since the beginning sometime around the 2000's that dams are vulnerable to drought and can't be relied on their own for backup of solar and wind. This is one reason why their was opposition to the Snowy Hydro 2 along with it's cost.
Pumped hydro can play a part, especially if the lower water supply is plentiful. For short term duration (8 hours or so) batteries are now far more cost effective. Just with batteries alone AEMO's projections indicate the grid can get well above 90% solar and wind. We have at least a decade probably two before we have to settle on the best option for the last <10%.
Burning hydrogen H2 + O = H2O obviously doesn't produce any GH effect.
However H2 alone causes problems with other GH gases, but that's only if you accept that something of the order of a few PPM can have and effect. Perhaps today you will.
