This was originally published on LinkedIn by Roxby Hartley, Ph.D. on March 27, 2026.

Well, based on the latest research, there’s a strong case for treating it as one.  A “super pollutant” is typically understood as a gas that produces disproportionate warming relative to its mass and lifetime, often due to strong radiative forcing or system-level chemical interactions. The commonly cited examples are methane, nitrous oxide, and fluorinated gases. These are not dominant by volume, but they account for 50% of near-term climate forcing. Hydrogen does fit this definition through a different pathway, but understanding exactly how it does so allows risks to be managed.

Two recent papers agree. It has a high Global Warming Potential (GWP):

• GWP100: 11 ± 4 kg CO₂e per kg H₂: Ouyang et al. (2025). The global hydrogen budget. Nature, 648, 616–624. https://doi.org/10.1038/s41586-025-09806-1
• GWP100 11.6 ± 2.8 kg CO₂e per kg H₂: Sand et al. (2023). A multi-model assessment of the Global Warming Potential of hydrogen. Communications Earth & Environment, 4, 203. https://doi.org/10.1038/s43247-023-00857-8

Neither paper sets out to label hydrogen as a super pollutant. Instead, they explicitly model hydrogen’s behavior and interactions within the atmospheric system. Hydrogen is not a primary greenhouse gas in the way CO2 or methane are. Its direct radiative forcing is weak; its combustion products are water and NOx, with NOx levels dependent on temperature. However, the problem is how hydrogen affects atmospheric chemistry: it modifies the hydroxyl radical budget. Hydroxyl radicals are an important pathway for the oxidation and breakdown of many atmospheric gases, especially methane. They are the dominant mechanism for methane oxidation, turning methane into CO2 and H2O, and therefore regulate one of the most important short-lived climate forcers in the system.

Hydrogen also reacts with hydroxyl radicals, so as hydrogen concentrations increase, hydroxyl availability declines. The result is that methane removal slows, and its lifetime increases, leading to rising atmospheric methane concentrations. Hydrogen does not need strong radiative forcing to matter. It amplifies warming by extending methane’s lifetime.

The global hydrogen budget paper quantifies sources and sinks and shows that hydrogen is tightly coupled to atmospheric oxidation capacity. What was historically treated as a trace gas becomes material once scaled through anthropogenic systems. The GWP paper extends this by quantifying hydrogen’s effective warming impact through multi-model simulations. It shows that hydrogen’s climate effect is dominated by indirect pathways, primarily methane lifetime extension, with additional contributions from ozone and stratospheric water vapor. This is the basis for framing hydrogen as a super pollutant. Not because of its direct emissions, but because of how it alters the system governing other pollutants.

It is not as ‘bad’ as you might think: Most comparisons rely on global warming potential per kilogram. On that basis, hydrogen has a high GWP, albeit only 39% of methane’s. However, I am used to working with fuels, and fuel emissions are not typically measured on a per-kilogram basis; instead, fuels are measured in terms of emissions per unit energy. Hydrogen contains roughly 120 MJ per kilogram. Methane is closer to 50 MJ per kilogram. For the same unit of delivered energy, significantly less hydrogen mass is required. When climate impact is normalized per unit energy, hydrogen’s relative performance improves substantially. It is still significant, but certainly not as bad as a GWP100 > 11 kg CO₂e per kg H₂ initially seems to be. To put the scale in context, Ouyang et al. estimate that all rising atmospheric hydrogen between 2010 and 2020 contributed just 0.02°C of global surface warming. The practical implication is that a hydrogen economy can deliver the same energy services as a methane-based system while having a significantly lower warming impact, assuming the same leakage rate per unit of energy.

A 2026 LCA study (Serghini et al., International Journal of Hydrogen Energy) makes this concrete across six European ground transport pathways for green hydrogen. When hydrogen’s GWP100 of 12 kg CO₂e per kg H₂ (from Warwick et al., 2022) is applied to supply-chain leakage, the climate impact of each delivery pathway increases. In some cases, enough to push previously compliant pathways above the EU’s renewable hydrogen threshold of 3.38 kg CO₂e per kg H₂. Liquid hydrogen transport is most affected, with supply-chain losses nearly five times higher than compressed gas by truck. Liquid hydrogen storage requires active refrigeration or a ~1% by mass daily bleed-off to keep the gas in liquid form at < -253 °C. The study also finds that delivery-related stages, that is, conditioning, transport, and deconditioning, account for more than half of the total global warming impact across all scenarios, independent of leakage. The production of green hydrogen is not the problem; getting it where it needs to go is.

Hydrogen’s climate impact is mediated by atmospheric chemistry, making it sensitive to leakage (quoted as 1-10%).  Understanding that allows operators and system designers to:

• Set leakage thresholds based on climate performance
• Prioritize infrastructure that minimizes loss
• Design MRV systems that capture hydrogen emissions directly
• Understand the transportation mode trade-off against local production

This is the same transition that occurred with methane, but now it is happening earlier in the deployment cycle. Framing hydrogen as a super pollutant is not about limiting its use. It is about correctly identifying where its impact comes from so that it can be managed. Hydrogen remains a viable and, in many cases, advantageous decarbonization pathway. Once the chemistry is understood, the pathway to maintaining hydrogen’s advantage becomes clear: control leakage, measure it accurately, and evaluate performance based on the energy delivered across the full atmospheric system.