Changes in climate forcing from hydrogen deployment as a decarbonization strategy

Hydrogen deployment is projected to expand in energy transition scenarios to decarbonize hard-to-electrify end uses. Hydrogen is an indirect climate forcer, and increased hydrogen production and use may lead to an increase in hydrogen emissions, which could occur during production, delivery, and/or final consumption. At the same time, when hydrogen deploys in the energy system, other energy carriers such as liquid fuels, natural gas, coal, and electricity would be displaced, affecting both CO₂ and non-CO₂ emissions, including CH₄, SO₂, NOx, CO, NMVOC, and BC. To our knowledge, the full suite of potential climate forcing changes from hydrogen deployment has not been examined in existing studies, in part because it requires combining information from different fields. This study addresses this gap by using a well-known integrated assessment model (GCAM) to combine (1) credible hydrogen deployment scenarios that illustrate which energy carriers could be displaced by hydrogen; (2) information about hydrogen emission rates and emission factors of other climate forcers by technology, sector, region and time; and (3) a simple climate model capable of translating all relevant emissions, including hydrogen emissions, into changes in climate forcing. Across all scenarios considered, when compared to a scenario without hydrogen deployment for energy, we find that reduced forcing from CO₂ emissions dominates all other forcing changes. In addition, the net forcing change excluding CO₂ and methane, as well as the net indirect forcing change from CO, NOx, NMVOC, and H₂ is negative and small relative to the total forcing change. These results raise important questions for technology and policy assessment regarding the treatment of indirect and aerosol effects.