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What the latest IPCC report says about zero-carbon fuels 

November 11, 2022 Work Area: Zero-Carbon Fuels

Today is “Decarbonization Day” at COP27, and it is the first time the conference has dedicated an entire day towards discussing the complex portfolio of strategies and technologies required to decarbonize hard-to-abate sectors. CATF expects hydrogen, specifically hydrogen produced using low-emissions pathways, to play a significant role in today’s discussions given that many countries and regional blocs are adopting it into their decarbonization strategy. For example: 

  • The U.S. has passed legislation with hydrogen provisions that provide $8 billion towards the establishment of Regional Clean Hydrogen Hubs (Bipartisan Infrastructure Law) and up to $3.00 per kilogram (kg) of hydrogen produced, depending on the carbon intensity of the hydrogen (Inflation Reduction Act).  
  • The European Commission, which plans to produce and import 10 million tonnes of renewable hydrogen into the European Union by 2030, recently approved up to €5.2 billion in funding for research, development, and deployment of hydrogen infrastructure and technologies. The European Commission also announced the creation of a new European Hydrogen Bank that will invest €3.0 billion to help build the future hydrogen market.  
  • Egypt, the host country for this year’s COP, is also inviting investment in hydrogen by building an $8 billion green hydrogen production facility in the Suez Canal Economic Zone. 

Bills and commitments like these are “a major step forward for zero-carbon fuels” according to Emily Kent, Clean Air Task Force’s U.S. Director for Zero-Carbon Fuels. Zero-carbon fuels like hydrogen and ammonia contain no carbon—as the name suggests—and produce no CO2 when combusted. While electrification and the buildout of zero-emissions electricity will achieve much of the work of decarbonization, zero-carbon fuels like “low-emissions hydrogen [have] significant potential as a critical climate tool for addressing hard-to-decarbonize sectors of the economy like heavy transportation and heavy industry”. These sectors are currently served by high-emitting fuels and may be prohibitively expensive or commercially impossible to electrify.  

For an additional perspective and a summary of current scientific consensus, this blog takes a deep dive into the recent Sixth Assessment (AR6) Working Group III (WGIII) report from the Intergovernmental Panel on Climate Change (IPCC) to explore the IPCC’s view on the role of zero-carbon fuels as a climate solution. 

Hydrogen can help with short- and long-term load balancing of a 100% carbon-free electric grid  

The electric sector is the largest source of anthropogenic greenhouse gas (GHG) emissions. It accounted for around two-thirds of global emissions in 2019 (AR6 WGIII Report 6.3). Reaching a 100% carbon neutral electric grid will require the rapid deployment of a range of firm power resources such as nuclear energy, super-hot rock geothermal, and natural gas with carbon capture and storage. Variable resources, such as solar and wind, will also have a major role to play. 

The IPCC’s WGIII concludes that deploying more variable production will require greater grid flexibility from a “variety of systemic solutions”, including “electrolytic hydrogen and derivatives” (SPM C.4.3). For short-term balancing, hydrogen can be used as fuel for fuel cells or burned in gas turbines to create dispatchable power, thus providing “clean firm” electricity generating capacity to balance a grid with significant intermittent zero-carbon energy sources. One potential technical challenge involves adapting turbines to run on pure hydrogen and managing the associated nitrogen oxide (NOX) emissions formed through higher flame temperatures. Commercial turbine offerings already exist that can operate on up to 20 to 50% ratios of hydrogen in natural gas and many companies have already committed to making 100% capable ones by 2030.  

For long-term balancing, hydrogen can provide “electricity storage to support high-penetration of intermittent renewables” and “enable trading and storage between different regions” (AR6 WGIII Report In this context, ammonia can be a “cost effective hydrogen carrier” for grid-scale hydrogen usage given its higher energy density and comparative ease of liquefaction at temperatures below -33°C when at ambient pressures (AR6 WGIII Report If needed, ammonia can then be “cracked” back into hydrogen. Uncracked ammonia, like hydrogen, can also be used in fuel cells or burned in gas turbines to generate power. Though both are nascent technologies, their potential means that ammonia “could play a major role in forming [an interconnected] hydrogen and/or ammonia economy to support decarbonization” (AR6 WGIII Report 

Decarbonizing the industrial sector requires low-emissions hydrogen as feedstock and fuel 

The industrial sector is the second largest emitting sector and accounted for 24% of global emissions in 2019. When indirect emissions from electricity and heat generation are included, it overtakes the energy sector as the largest emitting sector at 34% of global emissions in 2019 (AR6 WGIII Report 11.2.2). WGIII provided two broad categories for how low-emissions hydrogen can decarbonize the industrial sector: feedstock and fuel switching. For feedstock switching, existing chemical processes that use hydrogen, such as ammonia production, can use a lower-emission version produced via electrolysis with clean electricity or gas reforming coupled with carbon capture and other emissions reductions measures. Gas-based direct reduced iron (DRI) processes for steel production also already use hydrogen, but this time in a mixture with carbon monoxide known as syngas. Syngas is used in these processes to reduce iron ores, thereby removing the oxygen from the iron oxide. The resulting sponge iron can then be fed into electric arc furnaces to make steel. Here, low-emissions hydrogen can replace up to 30% of the methane used to make syngas without needing to change the process. The eventual goal, which requires process changes, would be to replace the syngas entirely with only hydrogen, a feat that has already been demonstrated commercially in Trinidad.  

As a fuel, hydrogen can be used as a complete or partial substitute for carbon-containing fuels in process heating. High-temperature process heating in blast furnaces and in the production of primary chemicals are both examples where co-firing with hydrogen can help abate emissions. Here, WGIII cited the experimental work from the Course50 projects and Thyssenkrupp that demonstrated the potential to reduce emissions by 30 to 40% via hydrogen co-firing in blast furnaces and oxygen furnaces (AR6 WGIII Report 11.4.1). This decarbonization method is already being adopted in regions like the Port of Rotterdam where hydrogen will be used as fuel to abate 2.7 Mt of CO2 emissions as part of its H-vision project.  

As countries look to adopt policies that promote the use of low-carbon versions of internationally traded basic materials, WGIII predicts that “regions with abundant low GHG energy and feedstock have the potential to become exporters of hydrogen-based chemicals and materials processed using low-carbon electricity and hydrogen” (SPM C.5.3). 

Hydrogen can help decarbonize heavy-duty land transportation, but needs more mature fuel cells 

The transport sector is the fourth largest source of GHG emissions and accounted for roughly 15% of total GHG emissions in 2019 (AR6 WGIII Report 10.1.2). WGIII believes that hydrogen holds “significant promise for delivering emission reductions if it’s produced using low carbon energy sources” for “harder-to-electrify transport segments such as heavy-duty vehicles” (AR6 WGIII Report 10.3.3). This aligns well with CATF’s view on hydrogen’s use for land transportation: the high-energy requirements in heavy-duty land transportation pose challenges for battery-powered systems and mean that hydrogen fuel cell vehicles could be a key to fully decarbonizing the sector. Hydrogen is more likely to play a supplementary role in light-duty transportation markets.  

For hydrogen to play a greater role in decarbonizing heavy-duty vehicles, WGIII calls for further advances in fuel cell technology as it is still “not yet mature for many commercial applications” (AR6 WGIII Report 10.3.3). One example cited in the report is better fuel cell durability, which needs to approach the 30,000-hour range to be competitive with diesel vehicles. Fuel cells used in buses have demonstrated durability close to that range, while light-duty fuel cell vehicles are near the 4,000-hour range (Kurtz et al. 2019). CATF encourages both the public and private sectors to pursue research and development (R&D) to improve the performance of fuel cells to enable hydrogen to be a climate solution for the transportation sector. 

Low-emissions hydrogen will be vital as a fuel or feedstock for decarbonizing fuels in the shipping and aviation industries 

Unlike land transportation, WGIII predicts that “ICE [internal combustion engine] technologies are likely to remain the prevalent options for shipping and aviation. Thus, reducing CO2 and other emissions from ICEs through the use of low-carbon or zero-carbon fuels is essential to a balanced strategy for limiting atmospheric pollutant levels.” (AR6 WGIII Report 10.3.1).  

For aviation, WGIII clarifies that the “literature does not support the idea that there are large improvements to be made in the energy efficiency of aviation”—like advances to the propulsion system or optimizations to the aircraft’s design— “that keep pace with the projected growth in air transport” (Full Report 10.5.3). While shorter and smaller (i.e., less than 50 passengers) planes could be electrified, longer and larger aircraft will likely require liquid hydrogen, sustainably produced biofuels, and/or synthetic jet fuel. Hydrogen is vital to the production processes of the latter two; synthetic fuels use hydrogen as a feedstock and biofuels require hydrogen for desulfurization. So far, the industry has largely turned to biofuels, but CATF’s recent analysis shows that all of these options are likely needed to fully decarbonize the industry.   

For shipping, WGIII finds that “hydrogen and ammonia when produced from renewables or coupled to CCS, as opposed to mainly by [uncontrolled] fossil fuels with high life-cycle emissions (Bhandari et al 2014), may contribute to significant CO2-equivalent reductions of up to 70 to 80% compared to low-sulfur heavy fuel oil (Bicer and Dincer 2018b; Gilbert et al. 2018)” (AR6 WGIII Report 10.6.4). While liquefied hydrogen has a relatively low volumetric energy density compared to liquid fossil fuels, it is still higher than compressed hydrogen gas and batteries. Thus, it may be an acceptable fuel for certain short distance marine routes.  

Hydrogen and ammonia can both be used in gas turbines and ICEs or fuel cells to extract power. Ammonia can also be used to carry hydrogen given that it is easier to transport compared to liquid hydrogen. Beyond having a 50% higher volumetric energy density than liquid hydrogen, ammonia has an added advantage in that approximately 20 million tonnes per year (10% of the world’s production) are already transported via sea. As a result, numerous port facilities already have loading, storage, and transport infrastructure for ammonia in place (Gallucci 2021).  

To have a beneficial climate impact, hydrogen used in fuel or feedstock switching must have low GHG-intensity 

Figure 1. Life cycle GHG Intensity of heavy-duty trucking. Each bar represents the range of life cycle estimates, and the values were created using 100-year GWP values in the source data for each study. ‘ICEV’ refers to internal combustion engine vehicle. ‘HEV’ refers to hybrid electric vehicle. ‘BEV’ refers to battery electric vehicle. ‘FCV’ refers to fuel cell vehicle. ‘IAM EMF33’ refers to emissions factors for advanced biofuels derived from simulation results from the EMF33 scenarios. ‘PM’ refers to partial models, where ‘CLC’ is with constant land cover and ‘NRG’ is with natural regrowth. DAC FT-Diesel, wind electricity refers to Fischer-Tropsch diesel produced via a CO2 direct air capture process that uses wind electricity. ‘Ammonia and Hydrogen, low carbon renewable’ refers to fuels produced via electrolysis using low-carbon electricity. ‘Ammonia and Hydrogen, natural gas SMR’ refers to fuels produced via steam methane reforming of natural gas. (Source for figure and caption: AR6 WGIII Figure 10.8) 

To reap the full benefits of transitioning major emitting sectors to hydrogen, WGIII emphasized that the hydrogen used must have a low GHG-intensity (i.e., electrolysis using low-carbon electricity, gas reforming with very high rates of carbon capture and storage, very low rates of methane emissions in the natural gas supply chain, minimal venting/flaring, etc.). Shown above is an illustrative example: a review of life cycle emissions based on different transportation technologies and/or fuel types for heavy-duty trucks. The WGIII report contained these graphs for each type of freight technology except for aviation. For heavy-duty trucks, the life cycle emissions of using fuel cells powered by high-emissions hydrogen (i.e., reforming without carbon capture) is at times comparable to using diesel. In contrast, hydrogen, and hydrogen-derived fuels (Ammonia, FT-Diesel) produced using low-carbon renewable energy offer substantial emissions reduction compared to the existing fossil fuel alternative.  

Challenges and CATF Recommendations 

Low-emissions hydrogen, however, is not without its own challenges. Its efficacy as a decarbonization solution, as WGIII notes, will depend on its cost compared to conventional hydrogen and the high-emitting fuels it is replacing, the technology readiness level of specific end-uses, and the need for more widespread infrastructure (WGIII Another key challenge will be finding international alignment on a certification scheme, which is a crucial element that not only ensures that the hydrogen is produced using climate-beneficial pathways, but also establishes market confidence by accrediting trade between major hydrogen importers and exporters.  

CATF is helping to tackle these challenges through rigorous analysis, public policy design, public education, and advocacy, ensuring that global market, policy, and political conditions are ripe for a full transition away from high-emitting fuels to zero-carbon solutions. We recommend that stakeholders continue to invest in research, development, demonstration, and deployment (“RDD&D”) for the responsible development of low-emissions hydrogen production and use. RDD&D efforts such as the U.S Regional Clean Hydrogen Hubs will create learnings that can be shared across regions to catalyze further public and private investment and collaboration. Regions should also look to rapidly expand zero-carbon electricity, especially clean firm power, which will reduce costs for electrolytic hydrogen by allowing for higher electrolyzer onstream times. Supportive policy frameworks and market stimulation for carbon management infrastructure will likewise be vital in reducing costs for fossil-based hydrogen production with high rates of carbon capture and storage.  


IPCC’s WGIII clearly indicates that low-emissions hydrogen will be a key tool in the climate change solution toolkit. It also indicates that low-emissions hydrogen has immense potential in helping to decarbonize hard-to-abate sectors. Regions that understand this and want to adopt or further establish low-emissions hydrogen into their decarbonization strategies must also look beyond their borders. Resolving these policy, market, and research challenges will require more international discourse, collaboration, and consensus – and COP27’s “Decarbonization Day” provides a hopeful platform for these discussions to continue.  

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