Alternative fuel? yes. Greenhouse gas solution? no. Ammonia will (and does) leak into the environment where it becomes a part of the natural nitrogen cycle.

Alternative fuel? yes. Greenhouse gas solution? no. Ammonia will (and does) leak into the environment where it becomes a part of the natural nitrogen cycle. The end result of the natural nitrogen cycle is N2O (aka laughing gas) which is a greenhouse gas 250-350x more powerful than CO2. Running the world on ammonia, even if logistically possible, will likely accelerate climate change, not slow it.