hydrogen has a global warming potential 35 times that of carbon dioxide (CO2) in the first 20 years after its release into the atmosphere.
— Read on reneweconomy.com.au/is-australias-brown-coal-hydrogen-export-project-destined-to-fail/

why it doesn’t make any sense to export hydrogen or derived ammonia or methane. It might make sense send if used close to source to manufacture green steel etc. Japan has plenty ocean for wind farms to make its own hydrogen.