The current thinking is if we shift our energy needs from fossil fuels to hydrogen fuel we will eliminate the problem of global warming caused by CO2. The thought that strikes me is, If we shift to a hydrogen based energy will the water vapor created by hundreds of millions of cars and other fuel burning machines our modern society relies on cause an excessive amount of water vapor to be put into our atmosphere creating a larger problem due to the fact that water vapor has a more profound environmental impact in other ways such as increased rainfall over the planet.
The other thought I have is since we will be converting hydrogen into water on such a large scale, will this not eventually increase the total amount of liquid water on our planets surface, thereby raising ocean levels anyway? Should we be trying to emulate what nature does naturally by developing technologies which convert CO2 to usable energy thereby creating oxygen as a by-product. I would have to assume that since we are supposedly the smartest species on this planet that we could figure out how plants do this so efficiently and follow their lead.

Lucky we have rain !

Liquid CO2 is rather cold

Nature converts CO2 for us but we are busy wiping out the vegetation that does it. Water vapour will leave the atmosphere quicker as rain. We are already over the half way mark with oil and using more every year. It will become ever harder to get out of the ground so the problem will sort itself out eventually.

I watched an SF film the other day, one of these end of the world disaster movies. People had thought they still had lots of oil left and it suddenly run out on them. No more cars, they couldn't even move food about, so civilisation very quickly collapsed into chaos.