The foul-smelling fuel that could power big ships

That 1.8% number is pretty concerning, especially because the use of ammonia as a fuel would presumably result in a massive growth in its production and see those emissions grow with it. That makes the timing challenging-- do you try to build up end uses of ammonia fuel now before it's been sufficiently decarbonized and result in an increase in transportation emissions, or do you wait until we can make it more cleanly and then start to build out the fleet that can then use it? 

John, powering shipping with ammonia is a non-starter:

"NH3 is the principal form of toxic ammonia. It has been reported toxic to freshwater organisms at concentrations ranging from 0.53 to 22.8 mg/L. Toxic levels are both pH and temperature dependent. Toxicity increases as pH increases and as temperature increases. Plants are more tolerant of ammonia than animals, and invertebrates are more tolerant than fish. Hatching and growth rates of fishes may be affected. In the structural development, changes in tissues of gills, liver, and kidneys may also occur. Toxic concentrations of ammonia in humans may cause loss of equilibrium, convulsions, coma, and death."

https://water-research.net/index.php/ammonia-in-groundwater-runoff-and-streams