Last week, the International Maritime Organization (IMO) formally adopted its Initial GHG Strategy. This means that the shipping industry has committed to "reduce the total annual GHG emissions by at least 50% by 2050," and completely "phase them out, as soon as possible in this century."
This also means that a global industry is searching for a very large quantity of carbon-free liquid fuel, with a production and distribution infrastructure that can be scaled up within decades. The most viable option is ammonia. How much would be required? Roughly one million tons of ammonia per day.