It seems every day there is a new technology announced that will help us in the fight against global warming. These stories spark our imagination and give us hope.

But as time has gone on, we sadly learn that each basket of new technology contains fishhooks – unexpected problems and side-effects. Sometimes we only find these fishhooks when we dig really deep into a promising basket, which makes them all the more disappointing when we find them.

Electric cars are a good example. They give us almost all the convenience of the petrol cars we’ve come to know and love. But, as we’ve come to learn, the minerals used in the batteries come at an environmental and human cost – child labour in the Democratic Republic of the Congo to mine the cobalt for the batteries. Sure, we can avoid the greenhouse gas emissions of petrol vehicles, but there is still an environmental and social cost. It is a painful trade-off.

The latest example of a promising new technology is green hydrogen. It is a highly energetic fuel that can be created from nothing more than electricity and water and, when passed through a fuel cell to create electricity, makes only water again. Finally, we think, a clean and easily created fuel that can power our trucks, ships and planes!

Yet, just as our government is approving a $100 million subsidy for green hydrogen development over the next 10 years, we come to find some fishhooks.

It turns out, hydrogen is an intense but indirect greenhouse gas. Hydrogen released into the atmosphere readily reacts with hydroxyl radicals, short-lived gas molecules generated by sunlight. We depend upon those same hydroxyl radicals to remove methane and ozone from the atmosphere, both intense greenhouse gases. So, releasing hydrogen into the atmosphere, through leaks and upsets, will slow the natural removal of other harmful greenhouse gases, increasing global warming. The overall effect is still under study, but hydrogen is estimated to have a warming potential of approximately 100 times that of carbon dioxide over a 10 year period.

And, hydrogen is a notorious leaker. Being a very small molecule, it leaks through nearly everything, including carbon steel and the high pressure carbon fibre tanks used for fuel storage and in hydrogen fuel cell vehicles. Engineering work on stemming those leaks has focused mainly on preventing leaked hydrogen from reaching flammable concentrations (i.e., more than 4% in air), but it is unlikely that we will be able to stop leaks altogether.

It is estimated that 2.7% of global hydrogen production in 2020 leaked into the atmosphere. As hydrogen use becomes more widespread in the world economy and hydrogen production increases, The International Energy Agency estimates hydrogen leakage of between 2.9% and 5.6% by 2050. This amounts to nearly 30 million tonnes of hydrogen per year in the high risk case.

And then we find that transportation has the highest leakage rates, with fuel trucks and storage estimated to account for 5% leakage with another 2.3% coming from the actual hydrogen usage.

So, here we face another painful trade-off, but in this case, it is trading one source of global warming for another. Do we risk prolonging the already intense warming of methane in the atmosphere (84 times the warming potential of CO2 over 20 years) in order to move people and goods with hydrogen-fuelled transport?

In the end, there are no easy trade-offs. Our only really effective strategy is to stop – stop driving and flying as much, stop buying things from far flung places and stop trying to engineer our way into a low emissions lifestyle as convenient as the one we’ve enjoyed until now. The planet’s climate is changing and so must we.

– Tom Powell, Climate Karanga Marlborough