Global Hydrogen Review 2024

GHG emissions of hydrogen and its derivatives

Highlights

  • In 2023, global hydrogen production emitted 920 Mt CO2. Nearly two-thirds of production was from unabated natural gas, which emits 10‑12 kg CO2-equivalent (CO2-eq)/kg H2; about 20% was from unabated coal, which emits 22-26 kg CO2-eq/kg H2. Between 75% and 95% of these emissions occur directly at the point of production, and can be reduced by carbon capture, utilisation and storage (CCUS). For hydrogen from steam methane reforming (natural gas), abatement costs are estimated at around USD 60-85/t CO2 for capture rates of 55-70%, and USD 85-110/t CO2 for rates above 90%. However, carbon capture alone is not sufficient; upstream and midstream emissions must also be tackled.
  • Hydrogen from electrolysers is emissions-free at the point of production, and so emissions depend on the electricity used. Emissions intensity from electricity generation should be below 200‑240 g CO2/kWh for emissions to be lower than steam methane reforming. Renewable electricity is emissions-free at the point of generation, but embedded emissions can occur in the construction and manufacturing of renewable assets. Such emissions are currently not included in most standards and schemes; they can range from 0.4-2.7 kg CO2-eq/kg H2.
  • The process of converting hydrogen to a carrier for transport incurs energy losses of 45-70%. This means that any GHG emissions from the electricity input to the electrolysers increases by a factor of 2-3 in terms of the final hydrogen delivered. The lowest emissions are achieved when the electrolyser uses renewable electricity, and the hydrogen transported is used as shipping fuel and no fossil fuels are used in hydrogen recovery. Liquid hydrogen results in the lowest emissions due to its higher pathway efficiency (above 50%); emissions are slightly higher for liquid organic hydrogen carriers (LOHC) and ammonia.
  • The emissions reduction offered by carbon-containing hydrogen-based fuels is greatest when the CO2 source is biogenic or from the air. The emissions intensity of their electricity input should be lower than 160‑190 g CO2-eq/kWh for synthetic methanol and 95‑140 g CO2-eq/kWh for synthetic methane and kerosene to result in lower emissions compared to a fossil fuel. In emissions accounting, the way CO2 emitted during fuel combustion is allocated along processing steps in the supply chain has a large effect on the total emissions allocated to the individual product.
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