I'm confused. If we're stipulating carbon-neutral liquid fuel from renewable energy, what precisely is wrong with depolymerizing organic matter into ordinary hydrocarbons? Sure it generates CO2 at the point of use, but it's offset by the photosynthesis that made the organic matter. As long as the carbon cycle is a closed loop there shouldn't be problem, right?

I don't think the closed loop argument is sound. We care about the total amount of carbon in the loop, we care specifically about the amount in the atmosphere. That's the equilibrium point, and there's a lot you can do to push around the equilibrium point in a closed system.

Consider - we've been digging up ancient, sequestered carbon and putting it in the atmosphere on a mass industrial scale for hundreds of years. I don't think that anything we can do within the confines of a closed loop system is going to remotely compare with that.

Or, to put it another way - we've been treating the atmosphere as a sink. But if we stop digging up carbon, we'll still need carbon, and it will become a source instead. By buffering that resource into fuel stocks and plastics and everything else we use carbon for, the only direction CO2 levels can go is down.

Cargo/freight shipping could be a prime target for a cleaner ammonia base fuel as most of the ships currently run dirty semi-processed petroleum, “bunker fuel”. It’s a hyper-cost sensitive market so without regulation I’d doubt ammonia would compete. Still it could be a feasible option to reduce pollution. Some Western countries might accept ammonia or similar diesel replacement, as it’d be a sort of natural tariff, but likely China would lobby hard against such a measure. There’s have to be a very strong push from a few nations, which I’ll doubt we’ll see anytime soon.

What is the energy return of energy invested on getting hydrogen from solar and then turning into ammonia?

It's really poor, you need at least hydrogen for seasonal energy storage.

Are you counting the energy cost of preventing or mitigating climate change?

It's not as good as plugging ibto the mains or using batteries, but it could well be the best option for industrial hydrogen, large boats and planes.

So we need to add into EROEI all the energy needed to deactivate/retrofit de old technology used in planes and large boats. If I don't do this exercise I will be as in denial as the ones that don't believe in climate change. We need to reduce air and maritime travel. We need to invest in trains and also avoid unnecessary travel. Fuel taxes in the previously mentioned sectors may be a good option because at the moment they don't have taxes on externalities. We have only a few years to prevent climate change getting out of hand and there are simple and effective solutions. We do not have a carbon budget for solutions that are not yet viable on paper.

> Liquid ammonia has higher energy density than liquid hydrogen

Why not rockets then?

Methane is better than ammonia (less toxic, similar performance), while hydrogen is also still better (less toxic, higher performance), and hydrazine is also better (still toxic, but hypergolic with certain oxidizers).

It has been used in rockets, but there's usually better choices.

I'd be suspicious of anything people would prefer hydrazine over. ;-)