The key point in this discussion is to keep in mind that neither hydrogen, electics, hybrids, ethanol, nor diesels is THE single answer. There is a place for each and every one of them in the grand scheme of things. The mindset that often prevails is that there is some sort of panacea out there that will answer the mobil energy needs for the future. In my opinion there isn't. We are not likey to replace kerosene for flying airplanes due to the energy density. An electric will work fine in a retirement community. You are not going to tow horse trailers with an electric pickup. Hybrids can save fuel if the system can be optimized for the mission at hand. Hydrogen certainly has a place IF a reasonable means of generating hydrogen can be created (that is the problem, not making the fuel cell work!) In the meantime the consumer/traveler/commuter/etc. has to have some means and incentive to utilize and adopt the technology that fits their needs most. The single means of doing this that has been successful todate is fuel prices. When gas costs $2.00 the choice is easy....whatever gas engine that comes along. When fuel costs $6.00 a gallon it makes perfect sense to adopt the technololy that saves the most fuel for that particular usage and the consumer can make the decision that is BEST FOR THEM rather than having someone legislate what they THINK they need.
The inescapble political part here is that legislating higher fuel prices to act as an enabler for alternate fuels and alternate technology is viewed as political suicide. Instead, it is easier to legislate ignorant ideas like CO2 limits and transfer THE PROBLEM to the backs of the autocompanies. Politically correct for the politicians but, unfortunately, it drives exactly the WRONG sets of decisions down the chain....and people fall for it.
I think the first thing to do with the whole issue of fuel economy, greenhouse gases, alternate fuels, etc. is EDUCATION. If people start to understand some of the fundamental underlying principals the whole thing makes more sense and they can see thru the political maneuverings going on...maneuverings that are going to hurt all of us in the long run.
BTW......IF (and that is a big IF) there could be created a reasonable source of hydrogen it does make a lot of sense. Hydrogen is most often associated with fuel cells but hydrogen can run fine in a plain ole' spark ignited internal combustion engine given a few simple changes. It runs great, actually.
If you didn't want to wade thru the Jestalia Chronicals thread to discover the lost post you might want to check out
https://www.geocraft.com/WVFossils/GlobWarmTest/start.html This presents several scientific FACTS that might change your viewpoint on global warming and what can actually be accomplished with motor vehicles.