And not only is water vapor a greenhouse gas, it’s far and away the most abundant. What will millions of cars spewing water vapor into the atmosphere do to the climate I wonder?
Not a #### thing, just like the CO2 emissions aren't doing a #### thing...
Absolutely nothing.
We already have many, many thousands of cubic miles of water directly exposed to the atmosphere, into which it can evaporate whenever the conditions are right. One hurricane puts more water vapor into the atmosphere than all the hydrogen cars man could operate for 1000 years. BTW, a primary exhaust emission of gasoline or diesel powered vehicles is water vapor.
Up to 2% or so of the atmosphere is composed of water vapor. The major factor controlling how much water is in the air is temperature. Warm things up and water evaporates into the air. Cool things down and water condenses back out. Also known as rain and snow.
They already do. When petroleum is burned, slightly more water is produced than carbon dioxide.
Burning pure hydrogen simply removes carbon from the equation.
Petroleum is a hydrocarbon (that means it's made up of hydrogen and carbon for those of you in Rio Linda). The hydrogen becomes water and the carbon becomes carbon dioxide.