Is Hydrogen Fuel Bad for the Environment?

Hydrogen fuel leaks are being investigated and labelled as the “new methane slip”, is this a fact or an excuse to continue the use of fossil fuels?

Hydrogen fuel leaks are being investigated and labelled as the “new methane slip”, is this a fact or a way for the industry to maintain the relentless use of fossil fuels?


The urge to decarbonize activities globally is accompanied by heavy questioning about which strategy would be best to follow in terms of fuels and powertrains. Methane, being a potent greenhouse gas that comes from the utilization of natural gas, was initially perceived as the ultimate short-term alternative fuelling option by many of its advocates within the shipping industry. It was only a matter of time until the catastrophic consequences were brought to light, due to the unavoidable methane slip.

Consequently, potential hydrogen fuel leaks are being investigated and labelled as the “new methane slip” when in fact, their claimed indirect potential Greenhouse effect, contains a significant level of uncertainty and is heavily based upon the relentless utilization of fossil fuels.


Shipping decarbonization is part of a global effort to eliminate Greenhouse Gas Emissions for bringing global warming to a halt. The transportation sector is responsible for 16.8% of the total greenhouse gas pollution, with shipping contributing 2%, a number that is presented as “low” compared to the rest of the sector, especially when taking into account that shipping is responsible for 90% of the world’s global trade by weight. This can be attributed to a slight hesitation towards change within the maritime industry. Nevertheless, greenhouse gas emissions are only part of the greater problem, which is environmental pollution.

Sulfuric Oxides (SOx), Nitric Oxides (NOx) and Particulate Matter (PM) are some of the resulting emissions that come from the combustion of fossil fuels. These types of harmful emissions cannot be converted to a greenhouse gas warming potential such as that of Carbon Dioxide (CO2), either because they do not contribute to climate change at all, or because their effect is indirect.

Is Hydrogen Fuel Bad for the Environment?
Figure 1. Exhaust pollution as a result of fossil fuel combustion

This is the case with sulfuric oxides, where their presence in atmospheric clouds aids towards the reflection of heat coming from the sun instead of trapping and re-emitting it on the earth’s surface, as is the case with CO2. Although sulphuric oxide emissions are proposed as a method to enable geoengineering and reduce the planet’s temperature, this is only achieved temporarily.

Inevitably, SOx will be deposited from the atmosphere through water droplets, finding their way into people’s bodies through water ingestion and posing a major risk towards cardiovascular diseases. NOx emissions follow a similar pathway to that of SOx, with their health implications being mostly related to the respiratory system, related to rising cases of Asthma globally.

Scientists warn global warming will accelerate - due to reduction in ship pollution
Scientists warn global warming will accelerate – due to reduction in ship pollution

A new study published in Oxford Open Climate Change, suggests global warming will accelerate due to reduction in ship pollution

Ship Nerd

Finally, the health-implicating mechanisms of particulate matter emissions, (PM2.5 & PM10 measured in microns) arise due to their ultrafine particle size, which allows them to find their way into our bloodstream through respiration and ingestion. Due to the plethora of toxic chemical substances and metals they can be formed out of, PM can be linked to respiratory, cardiovascular, diabetes mellitus and Parkinson’s diseases.

All emissions described are the result of fossil fuel combustion, which although mostly comprised of hydrocarbons, certain impurities such as sulphur and heavy metals can be traced through the final fuel mixture. These impurities along with the high temperatures obtained during combustion, lead to the formation of molecules and particles such as the ones described above, hence, using “cleaner” fuels will allow for the elimination of most of the harmful emissions used. The most popular alternative fuel options that still rely on the utilization of internal combustion engines are Bio-diesel, ammonia and methanol. In the meantime, hydrogen fuel is being promoted as a zero-emission alternative meant to be utilized through fuel cells, a different type of powertrain.

Resistance toward change explained

Like most alternative fuels and powertrains proposed over time towards the maritime industry, hydrogen fuel is also faced with some scepticism. Ships of all sizes and purposes are designed to operate in remote and unsafe scenarios, with a potential failure point being the likely cause for fatalities and extreme environmental pollution, rendering ecosystems uninhabitable, such as in the case of Exxon Valdez. Accidents and failures such as these, give rise to the development of strict regulations and the development of fail-safe systems, such as double hulls, that have a significant impact on the overall design of each ship.

Is Hydrogen Fuel Bad for the Environment?
Figure 2. Exxon Valdez Oil spill, 1989 (RGB Ventures)

As one might understand, this is a time-consuming and capital-intensive process that significantly impacts each vessel, specifically the costs of operation and ownership. Consequently, when new and untested anti-pollution technologies are proposed over “traditional” and “well-proven” powertrains, such as the ones fuelled by diesel, to mitigate climate-changing emissions, ship owners along with managers and operators are left to face risk-managing decisions, with any unwelcome possibilities directly translating to loss of profit.

Hydrogen Fuel vs LNG

The heavy questioning against hydrogen fuel comes from its comparison with LNG (Liquified Natural Gas), which requires a significant amount of energy to be converted into a liquid while also being mostly comprised of methane.
What is Methane? Methane is a very potent greenhouse gas that is estimated to be almost 30 times worse than CO2. Initially, LNG advocates praised this new energy source for being significantly better than conventional diesel fuels, due to its lack of SOx and PM-inducing impurities.

At the same time, LNG combustion releases 25% less CO2 than diesel, resulting from basic stoichiometry and a higher energy content per mass. That said, basic stoichiometric equations cannot replicate the combustion characteristics of engines onboard a vessel realistically, where a small part of the fuel mixture is not combusted and escapes through the exhaust valves, causing the infamous methane slip.

Like in the case of hydrogen fuel, LNG’s volumetric energy density is rather low, compared to diesel or even methanol, requiring larger fuel tanks to maintain the same energy storage, which is not welcomed within the maritime industry, in worries of sacrificing revenue-generating cargo space. The liquid hydrogen fuel volume comparison with diesel is illustrated in Figure 3.

Figure 3. Comparison of fuel storage capacity between Diesel and Liquid Hydrogen

Is Hydrogen Fuel Bad?

So far, all studies conducted to investigate hydrogen fuel impact towards the greenhouse phenomenon, point out that hydrogen itself cannot be considered a greenhouse gas. However, this does not limit its interactions with other greenhouse gases, which raises concerns for scientists aiming at climate improvement.

Interaction with GHGs

According to relevant studies, hydrogen fuel molecules that have leaked into the atmosphere, tend to react with free hydroxyl radicals (OH), one of the most important oxidants in the atmosphere, which in turn, disturb the lifetime of methane, the concentration of ozone (O3) in the troposphere, cause an increase in water vapour abundance in the stratosphere and affect the production of aerosols. The relevant chemical reactions can be found below:

(1) Hydroxyl reactions caused by the presence of Hydrogen

\begin{gather*} H_{2}+ OH=H_{2}O+H \end{gather*}

(2) Non-occurring Methane dissociation due to lack of Hydroxyl as a result of reaction (1)

\begin{gather*} CH_{4}+ OH=H_{2}O+CH_{3} \end{gather*}

(3) Formation of Hydrogen Peroxide (HO2) resulting in Water vapor

\begin{gather*} H+ O_{2}=HO_{2}, \end{gather*}
\begin{gather*} HO_{2}+ OH=H_{2}O(vapor)+O_{2} \end{gather*}

(4) Formation of Ozone the presence of reactive oxygen, NOx, and sunlight

\begin{gather*} ReactiveO_{2}+ NO_{x}=NO+O_{3} \end{gather*}

The four key gases can significantly impact the greenhouse effect, which therefore can classify hydrogen as an indirect greenhouse gas, with a Global Warming potential (GWP) over 100 years lifetime being 5-12.8 times worse than CO2. At a glance, this appears to be a detrimental finding, easily outweighing the net zero capabilities hydrogen fuel can offer. Nonetheless, one must understand the conditions through which the other reacting gases appear in the first place.


The first one, methane, is mostly traced back to human activities such as the transportation, energy production, agricultural and waste management sectors. By prolonging the lifetime of methane, ozone and vapour concentrations are affected within the stratosphere and troposphere, thus considered as secondary reactions. One could easily point out that a similar result could be achieved by an increase of methane leakage, even without the presence of hydrogen, hence it could be argued that limiting methane slip is a priority.

Nitrogen Oxide NOx

NOx also plays a significant part in ozone formation (Chemical Reaction 4). Hence, its emission’s point source should be considered. NOx emissions can occur naturally through the presence of lightning due to the extremely high temperatures attained, which is in line with the operational conditions in internal combustion engines.

As a natural progression of thought, one must question what the main source of nitrogen oxides is, where the answer to that is yet again, internal combustion engines within the transportation, energy production and other industrial sectors.

Sulphur Oxides SOx

The same story applies to atmospheric aerosols that are sulphur-based (SO4), which require SOx emissions’ presence to be formed. Noteworthy, is the advantage yield of fuel cells, meant for hydrogen fuel utilization, highly efficient electrochemical devices that allow for lower operating temperatures during energy production, eliminating NOx emissions.

Hydrogen Leak

Important to note, is the large uncertainty of the studies published relevant to the GWP-100 predictions concerning hydrogen fuel leaks. One of the most popular, recent (2023) and extensive model-based studies conducted by the Center for International Climate Research, reached a mean GWP value of 11.6 in CO2equiv. with a margin of error of around 25%, as there is significant uncertainty in factoring in soil uptake, photochemical production and the overall lifetime of hydrogen fuel. The final result is also a mean value between five global atmospheric chemistry models which could provide more credit.

Unfortunately, a number of questionable, by the scientific community, reports have also been released to address this topic, where the results attained are based on exaggerated leak predictions.
Hydrogen leaks are currently predicted based on the estimated leaks for methane. Although it is a sound starting point, many consider this a false assumption since the two gases behave differently in the event of a leak, mostly due to the smaller molecule size and significantly lower density of liquid Hydrogen fuel, compared to LNG.

To continue, hydrogen fuel will probably not be treated as current fossil fuels. Instead, the entire point would be to transition from fuel extraction and distillation (a major leak point) to local production, via electrolysis through renewable electricity. This will aid towards minimizing energy losses, from a Wind-to-Wake perspective (read here), and reduce the cost of production, as Hydrogen fuel is expected to cost significantly more than current conventional fuels (per kg).

Electrification of current infrastructure to cover energy demand, which was previously met through the burning of fossil fuels, is an important condition which needs to be fulfilled in order to produce green hydrogen fuel and reach zero emissions, further reducing the effects of methane slip and other greenhouse contributing emissions.

Take Home Message

New energy sources will require new methods of evaluation. Simply stating that a proposed solution which will enable zero emission activities is not enough and must instead be evaluated through every means necessary as it is humanity’s well-being at stake. Therefore, when said solutions are faced with subjective criticism, meaning to preserve the current, destruction towards the environment and the population’s health, the scientific community should step forward.

Hydrogen leaks could indeed pose a threat towards the environment if they occur at the same time as fossil fuel utilization. Unlike SOx emissions, hydrogen leaks in the earth’s atmosphere do not mask the damaging implications fossil fuel utilization has towards the environment, but instead, bring them to light. Consequently, people should instead emphasize on reducing the use of fossil fuels, electrify current infrastructure with renewable energy sources and finally produce hydrogen fuel only for industrial sectors that rely on integrated fuel storage, to move the world forward.

Finally, fuel leaks of all nature must be prevented, whether traditional or “new edge”. All fuels can pose major risks to the environment in some way, with hydrogen fuel making an exceptional case for saving a lot of money for producers, through leak elimination of the precious fuel, preventing accidents along the way.


See Also

LNG offers many benefits as a transitional ship fuel. However, certain engine types have been found to release significant amounts of unburnt methane slip, a powerful climate gas.

Methane, the main component of natural gas and LNG, has a global warming potential (GWP) of 29.8 times that of carbon dioxide (CO2) over a 100-year timeframe, according to the Intergovernmental Panel on Climate Change (2021). Preventing methane slip from escaping anywhere along its supply chain is therefore crucial as the world tries to contain the causes of climate change.

Methane Slip in LNG 4-stroke Otto-cycle engines
Methane Slip in LNG 4-stroke Otto-cycle engines

LNG offers many benefits but certain engine types have been found to release significant amounts of unburnt methane slip, a powerful climate gas.

Ship Nerd