HYDROGEN: Climate and environmental impacts of hydrogen emissions

There is an increasing interest in the role of hydrogen in the energy transition towards a low-carbon society. Hydrogen is considered a low-emission energy carrier when it is produced with renewable energy. However, when hydrogen is transported or stored for usage, some fraction of the gas is likely to leak out. Hydrogen has been recognized as an 'indirect greenhouse gas' in international climate assessments since 1990. This is because hydrogen is involved in many chemical reactions in the atmosphere which affects the concentrations of other gases that have an impact on the climate, mainly methane and ozone. Nevertheless, there are few studies that have quantified the total climate effect of hydrogen, and there is a lack of estimates for the global warming potential of hydrogen; GWP100. Hydrogen stays in the atmosphere for about two years. It is removed from the atmosphere by uptake in soils and by oxidation by OH, an extremely reactive gas in the atmosphere. Methane is also removed by oxidation of OH, so when more hydrogen reacts with OH, less OH becomes available for methane decay. Increased hydrogen levels will therefore increase methane levels in the atmosphere. Second, in the troposphere, the hydrogen atoms rapidly go through a reaction chain that produces ozone. Third, hydrogen leakages might also lead to a change of the ozone layer via increased water vapor at high altitudes. The magnitude of these effects is not clear, and they are interconnected and subject to feedbacks. In this project we will use five different state-of-the-art global chemistry models to investigate the climate and environmental effects of hydrogen leakages and provide new estimates of GWP100. We will also investigate the trend in the atmospheric concentration of hydrogen, which has increased since pre-industrial times from 350 parts per billion to about 550.

There is an increasing global interest in hydrogen as an energy source to replace fossil fuels. This summer, Norway released its first hydrogen strategy to stimulate the development of hydrogen-related technologies, and the strategy highlights hydrogen as an important contributor towards a low emission society. Around the same time, the EU released its ‘Hydrogen Strategy for a climate neutral Europe’ where hydrogen is set as an investment priority. However, despite the willingness of policymakers to stimulate a transition to a hydrogen economy, little attention has been paid to the potential environmental challenges of such a transition. Before introducing hydrogen technologies on a large scale, we need to thoroughly assess hydrogen’s impact on both the environment and the climate. With today’s technology, it is almost impossible to fully prevent hydrogen from leaking. When hydrogen is made, transported, and stored, some fraction of the gas will spill. Therefore, enhanced use of hydrogen will lead to increased hydrogen emissions. This will influence the chemical composition of the atmosphere, in particular the concentrations of methane and ozone. An increase in methane and ozone may contribute to global warming, while changes to the ozone layer influences the amount of harmful UV radiation reaching Earth’s surface. Ozone is also toxic to humans and animals and may reduce crop yields. The effects of hydrogen depend on complex chains of chemical reactions. At present, only a few studies have considered these aspects. The uncertainties are substantial, and none have investigated all the climate and environmental effects. Together with world leading experts, HYDROGEN will address these knowledge gaps by using comprehensive and consistent state-of-the-art modelling with realistic scenarios and background states, to fully understand the climate and environmental effects of deploying hydrogen technology.