Are you kidding? What do you think water is? It is burned hydrogen. Also, water vapor is much more of a 'greenhouse gas' than CO2. Do you know what the CO2 percentage in the atmo is?
Just before you burn hydrogen or hydroxy (hydrogen/oxygen gas mix), you have separated the hydrogen and oxygen molecules from water. Upon burning hydrogen or hydroxy, the by product is water. No more than what you started with. What's the problem? Is carbon and sulfur emissions some how better? Of course CO2 would be generated if fossil fuel plants where being used to supply electricity for electrolysis. However, there are other pollution free means. Little wonder we are stuck in fossil-fuel consciousness with the fear and negativity exhibited by many people. Personally, I don't feel that hydrogen is the big wave of the future, so much as up coming developments in new high efficient solar and wind technologies to produce electricity, and new generations of fast charging super-capacitors as energy storage. It's not unlikely that in ten years we'll have exceptionally practical, pollution free, electric vehicles with range and speed better than gas powered cars. It would likely be sooner if there was more help from the government, but they are the epitome of foolish-fossil-fuel-consciousness. They are a dying breed. j