Is Hydrogen as Clean as We Think? Scientists Uncover Overlooked Emissions

By Muhammad OsamaReviewed by Laura ThomsonMar 6 2025

In a recent article published in Communications Earth & Environment, researchers explored the impact of hydrogen leakage on the life cycle climate effects of hydrogen supply chains. Their goal was to provide a comprehensive life cycle assessment (LCA) of various hydrogen production methods while evaluating the environmental consequences, particularly the indirect warming effects caused by hydrogen emissions.

Advancement in Hydrogen Technology and Its Role in Decarbonization

Hydrogen has emerged as a key technology for decarbonization, especially in sectors like heavy-duty transportation and steel production. Unlike fossil fuels, its combustion does not release carbon dioxide (CO₂), making it a promising alternative for reducing greenhouse gas emissions. However, its indirect warming effects, particularly interactions with atmospheric methane and hydroxyl radicals, require careful evaluation.

As of August 2024, 61 countries, like the United States, have adopted national hydrogen strategies, reflecting its growing role in transitioning to a low-carbon economy. Policies like the Clean Hydrogen Production Tax Credit in the Inflation Reduction Act (IRA) aim to accelerate clean hydrogen production and adoption. Projections suggest hydrogen production could rise from 100 megatons (Mt) to 530 and 650 Mt by 2050.

Despite its potential, hydrogen’s life cycle greenhouse gas emissions remain a critical concern. The IRA’s tax incentives depend on hydrogen production's emission intensity, necessitating thorough emissions assessments across the supply chain. The Hydrogen Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (45VH2-GREET) model, developed by Argonne National Laboratory, serves as the official tool for quantifying these emissions but does not fully account for hydrogen leakage and fugitive emissions, which could reduce hydrogen’s overall climate benefits.

About this Research: Impact Assessment Through LCA

In this paper, the authors conducted LCA of different hydrogen production processes, including electrolysis and steam methane reforming (SMR), while considering hydrogen leakage and its indirect warming effects. They employed the 45VH2-GREET model to quantify emissions across the entire supply chain, from feedstock extraction to consumption.

The study examined electrolysis powered by grid electricity and renewable energy sources (solar and wind) and SMR with and without carbon capture and sequestration (CCS). To enhance accuracy, researchers applied a standardized leakage rate of 2% across all production methods. They utilized OpenLCA software and the IPCC impact assessment method to integrate leakage rates and global warming potential into their analysis.

Key Findings and Insights of Using LCA

The outcomes showed that considering hydrogen leakage and its indirect effects could increase the climate impact of hydrogen production by up to 0.5 kgCO₂e/kgH₂. However, factors such as electricity’s carbon intensity and methane emissions from the supply chain had a greater impact on overall greenhouse gas emissions.

The analysis indicated that wind-powered electrolysis consistently had the lowest emissions, while SMR exhibited the highest, failing to meet the U.S Energy’s clean hydrogen standard of 4.0 kgCO₂e/kgH₂. Even with high leakage rates, renewable-powered electrolysis achieved significant emissions reductions compared to fossil fuel-based methods.

Hydrogen’s climate benefits vary by application. In steel production, its use reduced emissions by 800-1400 kgCO₂e per ton of steel compared to conventional methods. In heavy-duty transport, the impact depended on the production pathway, highlighting the importance of selecting the right approach. Overall, production methods and feedstock emissions were the primary drivers of life cycle climate impacts, with hydrogen leakage contributing less than a 15% increase in emissions for most pathways.

Electrolysis powered by renewable energy consistently achieved over 60% emissions reductions, regardless of leakage rates. The study also reported variability in hydrogen leakage, with electrolysis showing rates between 2.0% and 9.2%, while SMR and SMR with CCS exhibited lower rates of 0.5% to 1.0%. These results highlight the need for comprehensive assessments considering direct and indirect emissions to inform effective policy-making and investment in hydrogen technologies.

Real-World Applications

This research has significant implications for industries aiming to reduce their carbon footprints. It suggests hydrogen can be an effective alternative for decarbonizing steel production and heavy-duty transportation. The authors emphasized prioritizing hydrogen use in sectors with the greatest climate benefits.

For example, hydrogen’s strong potential in steel production suggests that policies should support its adoption in this sector to maximize emissions reductions. Heavy-duty transportation's effectiveness depends on the production pathway, highlighting the need for careful selection to ensure meaningful climate gains.

The researchers highlighted the need for further empirical data on hydrogen leakage rates and more comprehensive models that account for all potential emissions sources. Understanding its life cycle impacts will be essential in shaping policy decisions and investment strategies as the hydrogen economy expands.

Conclusion and Future Directions

This study provides key insights into the life cycle climate impacts of hydrogen production, highlighting the need to understand its indirect warming effects. While hydrogen is a promising option for decarbonization, optimizing production, reducing leakage, and choosing suitable end-use applications are crucial to maximizing its climate benefits.

Future work should improve leakage estimates and explore new hydrogen production technologies that boost efficiency and cut emissions. As global investments in hydrogen infrastructure grow, these findings will be valuable for shaping effective policies and strategies for a sustainable hydrogen economy.

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