How do you know that?
Is CO2 a threat?
No, it's not. NOx, SO2, Ozone and all the other stuff that comes from carbon combustion can be a problem but with the exception of environmental hell holes like India or China or Mexico City, I wouldn't even consider them a "threat".
But once again, what does that have to do with the potential economics of using H2 as a transport fuel? Why have you made up your mind that it is impossible?
A little over 100 years ago, people likely thought the idea of a global petrol-based fuel transport system was nuts. Where would we get all the oil? How could we distribute it? What would we do with all the "useless" hydrocarbon by-products of refining? Trying to think through all those technical and logistical problems in advance had to make their heads swim. No one person was smart enough to figure all of that out so some who considered themselves smarter than others probably said "it will never work and we shouldn't spend any money on it."
How would H2 be better suited for cars than gasoline or hybrid engines?
Energy wise I think we all agree that we get more energy out of the oil and its byproducts that we use to refine and distribute it. You agree?
Hydrogen only makes sense if we have sooo much extra energy that we can use it to achieve these other benefits of H2.
These benefits include reduced CO2 (if you think that's a benefit worth spending money to reduce), reduced NOx, SO2, etc, reduced dependence on nasty regimes for oil, reduced oil spills etc etc etc.
These are benefits, I agree. Are they worth what it would cost? Maybe. I think we keep getting mixed up on this thread between people who think H2 will reduce bad side effects of hydrocarbon use without realizing that it will take more energy (and money) to do it.
If you support massive construction of nuke plants to support the generation of H2, and the use of the H2 in cars in order to reduce our need for Arab oil, then we agree.
Solar power satellites would work as well.
If you don't think this transition will require a huge input of external energy, then you don't understand thermodynamics, not to mention economics.
And note that emissions in US cars have been reduced about 97% from 2 decades ago. Nox etc. is not a threat. This leaves one main output from cars that has not been reduced, CO2.
But once again, what does that have to do with the potential economics of using H2 as a transport fuel? Why have you made up your mind that it is impossible?
You need to hype the dangers of CO2 from cars in order to make even onsideration of gasoline alternatives worthwhile.
Other than being cheaper, more convenient, safer, well-integrated with existing infrastructure, flexible, robust, and easier to store, gasoline has no advantages over hydrogen.