The global hydrogen rulebook challenge: Accounting for the emissions we don’t see

As government and industry leaders gather in Rotterdam for the World Hydrogen Summit, the hydrogen sector is entering a new phase. The past several years were defined by announcements, ambition and supply targets. The next phase is being shaped by tougher questions: where hydrogen makes the most economic sense, how demand can be scaled in priority sectors and what rules will govern emerging global markets. 

Last month, the International Organization for Standardization approved new methodologies for calculating greenhouse gas emissions from hydrogen and ammonia production. As public funding, industrial policy and long-term offtake agreements — in countries across Europe, Asia and the Middle East — increasingly depend on emissions thresholds and certification systems, the methodologies underpinning those systems are becoming economically consequential, and not just technically important.  

The new methodologies are an important step forward. But they also reveal a growing gap between rapidly evolving science and the way hydrogen and ammonia emissions are currently being accounted for and addressed. 

Hydrogen and ammonia are more than a carbon story 

Hydrogen and ammonia are often discussed through a narrow carbon lens: how much CO2 (and in some cases, methane) they emit compared to fossil fuels. That comparison matters, particularly for sectors like steel, fertilizers, chemicals and shipping where alternatives remain limited. 

But hydrogen and ammonia also create other climate, safety, and environmental risks that are frequently overlooked in lifecycle assessments and policy frameworks. 

Hydrogen can warm the atmosphere when leaked or vented. Ammonia systems can release reactive nitrogen compounds that contribute to climate change, air pollution and ecosystem damage. These impacts may occur outside the smokestack, but they still affect the environment and ultimately determine whether these fuels deliver the climate outcomes policymakers and investors expect. 

Best practices exist to mitigate losses to the atmosphere and minimize risks. But as hydrogen markets mature and credibility and accountability replace ambition, these emissions can no longer be treated as secondary issues. 

Hydrogen loss could weaken climate benefits 

Hydrogen has an important role to play in decarbonizing hard-to-electrify sectors. But hydrogen is also a small and highly diffusive molecule that can be released during production, from pipelines, valves, compressors, storage tanks and end-use equipment. 

When released into the atmosphere, hydrogen contributes to warming by interacting with methane, ozone and water vapor chemistry. The Intergovernmental Panel on Climate Change recognized this effect decades ago, and scientific understanding has advanced even further since then. 

Science shows that current estimates of hydrogen’s warming potential are robust enough to inform policy and business decision-making now. Yet hydrogen’s indirect warming effects remain absent from the ISO methodologies. 

That omission matters because loss rates directly affect climate performance. Research suggests that every 1% hydrogen loss can erode near-term climate benefits by 3%. 

Since we need hydrogen for hard-to-electrify sectors — to enhance both energy security and fuel diversity — the takeaway is that hydrogen systems need to be built and operated with emissions performance in mind from the beginning. Strong system designs, leak detection, monitoring and infrastructure standards are essential if hydrogen is to deliver on its climate promise. 

Ammonia’s overlooked reactive nitrogen impacts 

A similar risk exists for ammonia, which is made from hydrogen, currently used in fertilizer production, and is increasingly being explored as a low-carbon fuel for shipping. 

Ammonia combustion does not release CO2, making it attractive to parts of the maritime sector seeking alternatives to heavy fuel oil. But ammonia’s overall emissions profile is more complex than many current accounting systems reflect. 

Ammonia itself is highly toxic, and its production handling(e.g. storage, transport, refueling and effluent management), and combustion can release reactive nitrogen compounds, including nitrous oxide (N2O), nitrogen oxides (NOx), and ammonia itself — either leaked across the value chain or emitted as unburned fuel in the engine (often called ammonia slip). Beyond direct emissions, NOx and ammonia can be transformed through the nitrogen cycle into additional N2O (referred to as “indirect N2O”) via atmospheric and environmental pathways. 

These emissions matter. N2O is a potent greenhouse gas (273 times more powerful than CO2 over 100 years), while excess reactive nitrogen input to the environment contributes to air and ozone pollution, biodiversity loss and aquatic ecosystem damage. 

The new ISO methodology includes direct N2O emissions from combustion, but other reactive nitrogen impacts across the value chain — including ammonia losses and the formation of indirect N2O — remain largely unaccounted for. 

That gap could become increasingly important as ammonia scales as a marine fuel. Our latest research finds that without effective controls, reactive nitrogen emissions from ammonia fuel systems could be up to 185% higher than those associated with current marine fuels. 

Standards must evolve with the industry 

None of this means hydrogen or ammonia should be dismissed. Both will play an important role in industrial decarbonization and clean transportation systems where direct electrification is difficult. But the next phase of hydrogen market development will depend not only on deployment volumes, but also on confidence that these systems are delivering genuine climate benefits. 

This is why standards matter. ISO deserves credit for creating a common foundation for hydrogen and ammonia emissions accounting. Consistent methodologies are critical for enabling trade, investment and international market development. But standards are not static. They need to evolve alongside the science. 

The hydrogen economy is being built now. Infrastructure decisions made over the next few years will shape energy systems for decades. 

What gets measured will shape what gets financed, regulated and ultimately deployed. If hydrogen and ammonia are to earn long-term public and political trust, future standards must account not only for carbon emissions, but also for the indirect climate effects that increasingly define these fuels’ real-world impacts