Is hydrogen a greenhouse gas?
Recent research has revealed that hydrogen has an indirect influence on atmospheric warming. We have to accept that there is no perfect solution to the climate change challenge. Even renewable technologies indirectly involve adverse effects through mineral extraction and manufacturing of components. So, this should not be considered a showstopper for the hydrogen economy. But what impact will hydrogen have on the atmosphere and how will this influence climate change in the transition to a hydrogen economy?
Hydrogen will be produced with a range of technologies and the production processes can give rise to emissions. But what we are interested in here is the ‘global warming potential’ (GWP) of hydrogen itself, which has recently come to the fore as a potential concern.
GWP is a measure of how much a substance contributes to global warming over a given period of time, relative to the contribution of carbon dioxide. It is calculated by comparing the ‘radiative forcing’ of a given mass of the gas to that of the same mass of carbon dioxide over 20, 100, or 500 years. This calculation considers the ability of the gas to absorb and emit infrared radiation, as well as its atmospheric lifetime and other factors that affect its warming potential.
Radiative forcing is defined as the difference between the amount of incoming solar radiation absorbed by the Earth's atmosphere and the amount of outgoing infrared radiation emitted back into space. Positive radiative forcing indicates that more energy is being absorbed by the Earth's atmosphere than is being emitted, leading to a net warming effect. Negative radiative forcing indicates the opposite, with more energy being emitted than absorbed, leading to a net cooling effect.
For example, the GWP of methane (natural gas) over a 100-year time horizon is about 30 times greater than that of carbon dioxide.[1]
Calculating the GWP of hydrogen is tricky, as it doesn’t absorb infrared radiation directly. However, it has an influence on the chemistry of both the troposphere and the stratosphere. Whilst not a greenhouse gas itself, it does have an indirect influence on radiative forcing. New research has shown that hydrogen increases the lifetime of methane, increases the tropospheric concentration, and decreases the upper stratospheric concentration of ozone, as well as increasing the concentration of water vapour - all of which influence the climate.
Hydrogen itself has quite a short lifetime in the atmosphere and is removed by oxidation to water or through uptake in soil. Currently this latter factor has significant uncertainty due to limited understanding of the processes involved and significant challenges associated with the geographical extrapolation of local measurements of hydrogen uptake.
Research carried out[2] has calculated the GWP of hydrogen over a 100-year time horizon to be 11 ± 5 which is more than double previous estimates.[3,4]
Is this a cause of concern given the promising hydrogen economy and our government’s trust in hydrogen as an important component in meeting Net Zero by 2050?
Adopting hydrogen as an energy source will reduce emissions of carbon dioxide and provide a significant climate benefit. Since co-emitted combustion species, such as carbon monoxide, methane, and volatile organic carbons (VOCs), are also reduced in the move away from fossil fuels this increases the climate benefit further.
However, since hydrogen has an indirect GWP, efforts should be made to reduce leakage during production, storage, transportation, and use, as these will reduce the benefits. To estimate how much hydrogen may be emitted through leakage in a future hydrogen economy, research undertaken[2] considered a scenario where 100 percent of the final energy consumption of fossil fuels in buildings is converted to hydrogen, 50 percent of fuels in the transport sector and 10 percent in power generation. This represents 23 percent of global energy consumption. They then set a notional lower bound of 1 percent of the hydrogen supply being lost to leakage. This scenario results in 9 teragrams per year of hydrogen emissions, less than half of the ~20 teragrams per year of atmospheric hydrogen currently emitted from fossil fuel combustion, which is negligible.
There is of course significant uncertainty in many model-derived estimates for hydrogen emissions. However, what is clear is that fears about the GWP of hydrogen do not represent a showstopper for the hydrogen economy, under the current climate emergency. Hydrogen can and will have an important role to play in future energy systems.
Adding value
Learn more about the role of hydrogen in the energy mix towards 2050 by downloading our complimentary research report, Hydrogen Forecast to 2050.
References
1 P. Forster, T. Storelvmo, K. Armour, W. Collins, J.-L. Dufresne, D. Frame, D.J. Lunt, T. Mauritsen, M.D. Palmer, M. Watanabe, M. Wild, and H. Zhang, The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, pp. 923–1054.
2 N. Warwick, P. Griffiths, J. Keeble, A. Archibald, J. Pyle and K. Shine, Atmospheric implications of increased hydrogen use, Department of Business, Energy and Industrial Strategy (London, UK), 2022.
3 R.G. Derwent, D.S. Stevenson, S.R. Utembe, M.E. Jenkin, A.H. Khan and D.E. Shallcross, Global modelling studies of hydrogen and its isotopomers using STOCHEM-CRI: Likely radiative forcing consequences of a future hydrogen economy, International Journal of Hydrogen Energy, 2020, 45(15), 9211–9221.
4 R.A. Field and R.G. Derwent, Global warming consequences of replacing natural gas with hydrogen in the domestic energy sectors of future low-carbon economies in the United Kingdom and the United States of America, International Journal of Hydrogen Energy, 2021, 46(58), 30190–30203.