How fugitive hydrogen emissions could act as a greenhouse gas

As a clean energy carrier, hydrogen offers a number of possibilities for decarbonisation in various sectors. However, fugitive hydrogen emissions—unintended leaks during production, storage, or transport—pose a lesser-known environmental challenge. 

Prone to leakage due to its small molecular size and high diffusivity, this atmospheric hydrogen can keep methane in the atmosphere for longer by reacting with compounds that typically break methane down, producing water vapor (a greenhouse gas) in the process.  

In 2023, a group of researchers used ‘a model ensemble of five global atmospheric chemistry models to estimate the 100-year time-horizon Global Warming Potential (GWP100) of hydrogen’, estimating ‘a hydrogen GWP100 of 11.6 ± 2.8 (one standard deviation).’¹  

To translate: hydrogen could trap between 8.8 and 14.4 times more heat than CO2 over 100 years.  

Hydrogen is highly prone to leaking 

The molecular size of hydrogen makes it exceptionally leaky. Its small diameter allows it to escape through tiny imperfections in pipes, valves, and storage tanks, even under high-quality containment systems. Preventing leaks requires advanced materials and infrastructure that can withstand the high pressures and low temperatures necessary for hydrogen storage and transport. 

One study estimated that hydrogen’s ‘leakage rates are likely to range from 1 to 10%’, which is somewhat higher than some estimates for fugitive emissions of methane – a persistent concern for regulators – to be about 2.3% (in the US, at least).^{2 3}

Transporting hydrogen often involves cryogenic cooling to liquefy it, as this significantly reduces its volume. However, maintaining hydrogen at cryogenic temperatures (−252.8°C) is energy-intensive and still prone to boil-off losses, where hydrogen escapes as gas due to warming. High-pressure gaseous storage and pipeline transport also face substantial leakage risks. 

Hydrogen’s tendency to diffuse through materials—including metals—adds another layer of complexity. Over time, hydrogen can cause embrittlement of pipelines and storage vessels, further increasing the risk of leaks. These technical challenges underscore the difficulty of achieving a zero-leak hydrogen economy. 

Atmospheric hydrogen can limit methane breakdown  

Hydrogen itself is not a direct greenhouse gas in the way or are. However, it indirectly exacerbates warming by interfering with the atmospheric processes that regulate methane, a much more potent greenhouse gas. 

Methane naturally breaks down in the atmosphere through reactions with hydroxyl radicals (OH). When hydrogen is emitted, it competes with methane for these radicals. This reaction reduces the availability of for methane degradation, effectively prolonging methane’s atmospheric lifetime.  

One study explains that ‘Hydrogen perturbs methane because it reacts with and thereby reduces the concentration of OH [hydroxyl radicals], methane’s dominant sink’ and that this influence on ‘the methane term dominat[es] the impact’ of hydrogen.⁴ 

However, the inverse is true, too: if methane emissions were to decrease, hydrogen would contribute far less to global warming. Hence, one study suggest that: ‘The extent to which future changes in hydrogen might affect atmospheric composition and climate will depend upon [...] emissions reduction in species currently emitted [...] including methane’.⁵  

More hydrogen might mean more ozone

When hydrogen reaches the stratosphere, it reacts with hydroxyl radicals and produces water vapor. This additional water vapor can contribute to the formation of polar stratospheric clouds (PSCs), which provide surfaces for chemical reactions that release active chlorine compounds capable of depleting ozone.

Hydrogen also reduces the availability of radicals and other reactive species that help maintain the balance of ozone production and destruction. By altering this balance, hydrogen emissions can indirectly contribute to stratospheric ozone depletion, particularly in polar regions during events like the polar vortex.

The reactive hydrogen species generated by fugitive emissions, such as (which includes and ), can participate in catalytic cycles that destroy ozone. The increase in stratospheric water vapor amplifies these effects, compounding the challenges associated with the recovery of the ozone layer.

Fugitive hydrogen emissions could increase atmospheric water vapour  

When hydrogen reacts with hydroxyl radicals in the atmosphere, it forms water vapor as a byproduct. Water vapor is the most abundant greenhouse gas, responsible for trapping heat and amplifying warming in the atmosphere – and when it condenses, it releases latent heat absorbed during evaporation. 

Importantly, increased evaporation from warmer oceans increases atmospheric concentrations of water vapor in accordance with the Clausius-Clapeyron relation (warmer air holds greater quantities of water vapor), producing a feedback loop. 

This isn’t the end of it, however. Eventual condensation of water vapor itself warms the atmosphere, which means that water vapor both traps heat as a gas and releases heat when it condenses, causing further evaporation, and so on. This dual role of water vapor highlights its unique contribution to amplifying climate warming. 

¹ A multi-model assessment of the Global Warming Potential of hydrogen. Sand et al. Communications Earth & Environment. 2023.  

² Climate benefit of a future hydrogen economy. Hauglustaine et al. Communications Earth & Environment. 2022.  

³ Assessment of methane emissions from the U.S. oil and gas supply chain. Alvarez et al. Science. 2018.  

⁴ On the chemistry of the global warming potential of hydrogen. Chen et al. Frontiers in Energy Research. 2024.  

⁵ Atmospheric composition and climate impacts of a future hydrogen economy. Warwick et al. Atmospheric Chemistry and Physics. 2023.