Which is the more powerful greenhouse gas water or CO2?
From wikipedia: “Water vapor is a natural greenhouse gas and accounts for the largest percentage of the greenhouse effect. Water vapor concentrations fluctuate regionally, but human activity does not directly affect water vapor concentrations except at very local scales.” But your question is a good one becuase this effect alone make prediction impossible and so in my opinion there is a lot of hype for very little scientific basis. I don’t believe the water created by hydrogen cars will amount to much.
