Popular mechanics examines various alternative fuels, but isn’t good at figuring out cause and effect.
Global warming is caused by too much greenhouse gases; Burning stuff creates carbon dioxide, a greenhouse gas. Burning stuff causes global warming. Not digging stuff up out of the ground.
Hydrogen is easiest to create by passing electricity through water. Electricity is mostly created by burning coal (heating water, turning turbine, yada yada yada). See point one. This has just been pointed out in an Age opinion piece on public transport.
Which is why ethenol, methenol, biodiesel, natural gas, electricity and hydrogen aren’t anti-greenhouse fuels; Solar, wind, hydro, nuclear and geothermal are.
Only electric batteries / hydrogen cells can act as crossover technologies from renewable generation sources to transport. Anything else is going to have water lapping at your front door in a century; but hey, Venice is a romantic city – and wouldn’t it be great if many more of the cities of the world were romantic like Venice?.