GREEN hydrogen — or at least the promise of it — can certainly power a press release with unbeatable efficiency. Whether or not it will ever do the same for the world fleet is hard to say.

Breathless claims regarding the allegedly limitless efficacy of this wonder gas land regularly in the Lloyd’s List editorial inbox.

Somebody built a hydrogen truck, someone built a hydrogen tug. BP has purchased 49% of a green hydrogen plant, inevitably at an early stage of feasibility. The website of one Siemens affiliate even hails it as “the fuel of the future, to stop climate change”.

Would that it were so. But look beyond the boosterism and the potential of this form of green power is only matched — and maybe even outmatched — by its formidable cost, inefficiency and uncertainty.

The principles behind its manufacture are sound enough and will be familiar to anyone who didn’t bunk off high school chemistry classes.

Green hydrogen is produced through the electrolysis of water, using energy generated from renewable sources. When consumed in a fuel cell, it emits only water.

With the world now faced with the challenge of phasing out fossil fuels that release greenhouse gases, this looks like much the holy grail.

As anyone who has ever read The Da Vinci Code will know, holy grails are wonderful things. But this one isn’t buried under the inverted pyramid outside the Louvre.

Green hydrogen is the bedrock ingredient for a range of the green e-fuels that will inevitably power shipping in future, including LNG, methanol and ammonia.

Some critics, particularly in the conservative think tank milieu, even contend that you get less power out of green hydrogen than you put in.

These organisations are frequently funded by fossil fuel interests and not always disinterested observers. But this is a scientific question, not an ideological one, and should be settled as such.

What is clear is that to make green hydrogen at scale, producers will require access to orders of magnitude more renewable electricity than is physically possible right now. And yes, we are using the term “orders of magnitude” correctly.

It is just about conceivable that renewable power could expand by orders of magnitude in the near future. But that is not a given.

Given that green hydrogen is being relentlessly hyped like a 1970s rock band newly signed to a major label, there were some welcome words of common sense on the topic contained in a report issued by the International Chamber of Shipping this week.

On the ICS’s projections, the global need for green hydrogen is around 500m tonnes a year. Production at that level would require about as much electricity as the entire world used from all sources in 2022.

But there is a Catch-22 of the kind which Doc Daneeka, the fictional protagonist who first formulated such dilemmas, would surely have appreciated.

If there were a better option than green hydrogen, you would be crazy not to choose it. But there isn’t a better option.

Nor will there be until someone finds a way to make captured carbon useful, or can convince an anxious Washington that diffusion to all comers of nuclear technology for ship propulsion purposes is a good thing.

Already we are seeing companies and countries walk away from big green boasts they made in the past few years.

If green hydrogen is ever going to happen for shipping, the International Maritime Organization must set targets it cannot later walk away from.

Albert Embankment should adopt a carbon price next year to provide the companies the confidence needed to shell out the billions of dollars of investment that will be required even to get the ball rolling.

But let’s end on a positive note. If shipping does become an early adopter, it will need the stuff in vast quantities.

This will necessitate the introduction of infrastructure such as pipes, tanks, port facilities that can greatly assist other hard-to-abate industries in making the switch.

If anybody is going to do it, it is probably shipping that will lead the way.