@jhm et al.
Look. Carbon Tax, the bottom line:
Despite all best of intentions, shifting taxation from fuel inputs to emissions outputs is a fast track to legislation for methane generated Hydrogen and with it Hydrogen Fuel Cell displacement of wind, solar, hydro, nuclear and anything else that is genuinely emissions free and puts Hydrogen instead of electricity at the head of the economic food chain when it comes to powering vehicles including pure electrics.
This means fracking and methane hydrates until the end of human civilisation which would be quite rapid.
Why? SMR of methane to produce hydrogen is the fossil fuel industry's most carbon intensive activity. King of the hill, can't be beat. 16.58 Kg CO2e per Kg of Hydrogen with the same total energy as a fuel as a gallon of gas that comes to 11.3Kg between extraction and consumption by the same metrics.
By mass it's even worse. 1.1% of hydrogen production in 2013 as a percentage of the weight of crude oil extraction was responsible for 10% of total vehicle emissions or 829 Million Tonnes attributable to Hydrogen alone or 3% of all man made emissions that year from all activities from cement and transport to heat, light and industry.
This is Before the risks associated with direct methane emissions to the atmosphere when used as a fuel or as a feed stock for hydrogen, one of which in particular practically guarantees human extinction: Methane Hydrate Extraction.
This also happens to be the bottom line of Japan's interest in promoting a hydrogen economy and the bottom line rationale for the Toyota Mirai. Methane Hydrates are the "Natural Resource" besides water and biomass and solar and wind and "The Fuel for the Next 100 years" according to Toyota's advertising - because that is exactly how much Methane Hydrate Japan assesses that it has in its territorial waters that it dreams will free it from being dependent on foreign oil and gas - including from their perspective foreign Natural Gas from the USA - making Hydrogen the ultimate stupidity for the USA to encourage with subsidies and credits from any and every angle.
Now I hate that this is the bottom line of a carbon tax but surely it is far more hateful to be in the dark about this until the freaking Atlantic or Pacific is in your living room and the food store is shut because all the food is extinct! At least this way one might have a hope of doing something about it compared to being left in the dark and conned blind until it's too late!