Cars are far from the only potential consumer. Sure, you might also use some of the hydrogen to power cars with fuel cells. Or you use it to charge EVs. Or you use the ammonia directly for grid electricity and heating. Or industrial processes.
You probably need relatively little water compared to other processes that evaporate/drain it (agriculture) or use it for run-through cooling (power plants). Even an ocean tanker full of water wouldn't make much of a dent into the flow rates of a river.
Molecular hydrogen is unpolarized while ammonia molecules can establish hydrogen bonds, thus packing them more densely under the same conditions.
For really dense hydrogen we would need its metallic form but that requires pressures you might find in the core of jupiter. The electromagnetic force is more convenient than gravity.
> [...] turning them into a commodity that can be shipped anywhere in the world and converted back into electricity or hydrogen gas to power fuel cell vehicles
> district heating produced on power from the grid is taxed as if produced on coal, as the power has no traceability.
Sounds like there is room for improvement. E.g. an agreement with an energy provider and tracking when it was used on demand as a sink for excess energy instead of base-rate heating.
There's at least another 1000% to squeeze out by using more lines of code at the compiler side. Look at the wasm movement that wants to bring highly optimized intransparent code blobs to the client side and web servers written in rust so they can deliver even more complex applications in this post-moore world. Of course they'll sacrifice debuggability in addition to accessibility on that altar.
Even the chinese government recognized that at least doing something about the coal smog is something in their own interest. My understanding is that the risk of civil unrest is what drives them.
> I, as a concerned citizen can do nothing against the corporations ruling our society
Defenestrations, torches and pitchforks have been traditional solutions to rulers not acting in the interest of the populace.
Of course more peaceful means are preferable but the option needs to be kept on the table to remember why we have and want democratic solutions in the first place.
Intensive farming only happens when the material is used in a profitable way. Growing things only to dump them in the oceans is only profitable with subsidies or carbon taxes.
Extensive farming would likely have the natural rate of sequestration.
> All in all, super-powered seaweeds could sequester around 173 million metric tons (190 million tons) of carbon each year, about as much as the annual emissions of the state of New York.
It's not that much in comparison to the emissions of the entire industrialized world.
Every bit helps of course, but it's not a magical solution to our problems.