Climate impacts of hydrogen emissions

Hydrogen has gained attention as a key component of future low-carbon energy and industrial systems, with demand projected to increase from 100 Mt per year in 2024 to up to 1,370 Mt per year in 2050. However, there are concerns about the climate impact of the associated increase in hydrogen emissions. In this Review, we discuss the sources and sinks of atmospheric hydrogen and the resulting climate effects, including the use of metrics and implications for policy. Despite not being a direct greenhouse gas, hydrogen raises levels of methane, tropospheric ozone and stratospheric water vapour, which are potent greenhouse gases. Estimates of the 100-year global warming potential of hydrogen converge at 12 ± 6 (90% CI). Such metrics are sufficiently robust to inform policy and business decision-making and to be included in climate impact assessments to maximize the benefits of a future hydrogen economy. However, substantial uncertainties remain, particularly in quantifying various sources of atmospheric hydrogen from human and natural systems (estimates have a range of 55–141 Tg per year) and understanding soil uptake rates (32–90 Tg per year). Future research should focus on improved quantification of hydrogen emissions, especially across the hydrogen system value chain, better constraints on the soil sink and a more complete representation of hydrogen chemistry. Although hydrogen is not a direct greenhouse gas, its interactions with atmospheric chemistry lead to indirect climate impacts. This Review discusses sources and sinks of atmospheric hydrogen, including uncertainties and data gaps, and how the warming effect of hydrogen emissions can be estimated and accounted for in policies and standards.