The global hydrogen trade is emerging as a critical component of the energy transition, enabling regions with abundant renewable resources to supply clean hydrogen to energy-intensive economies. However, the emissions associated with international hydrogen trade—spanning production, liquefaction, carrier conversion, and maritime transport—must be carefully evaluated to ensure net climate benefits. This analysis compares emissions from regional production versus import scenarios, focusing on key corridors such as Australia-Japan and the Middle East and North Africa (MENA)-Europe.
Hydrogen trade relies on converting hydrogen into transportable forms, primarily liquefied hydrogen (LH2), ammonia, or liquid organic hydrogen carriers (LOHCs). Each method incurs energy penalties and emissions, which vary depending on the production pathway and transportation distance.
**Liquefaction and Carrier Conversion Emissions**
Liquefying hydrogen for maritime transport requires cooling it to -253°C, an energy-intensive process consuming approximately 10-13 kWh per kg of hydrogen. If this energy comes from fossil fuels, emissions can reach 5-7 kg CO2 per kg of hydrogen. Renewable-powered liquefaction can reduce this to near zero, but availability varies by region.
Ammonia synthesis, a common hydrogen carrier method, involves the Haber-Bosch process, which emits 1.5-2 kg CO2 per kg of hydrogen when powered by natural gas. Using renewable energy or carbon capture can lower emissions significantly. Cracking ammonia back into hydrogen at the destination adds another 0.5-1 kg CO2 per kg of hydrogen, depending on the energy source.
LOHCs, such as toluene-methylcyclohexane, require dehydrogenation, emitting 2-3 kg CO2 per kg of hydrogen due to high-temperature processes. While LOHCs enable hydrogen transport using existing oil infrastructure, their energy intensity remains a challenge.
**Maritime Transport Emissions**
Shipping emissions depend on distance, carrier type, and vessel efficiency. For LH2, specialized cryogenic tankers are required, with boil-off losses of 0.2-0.5% per day. Ammonia, being easier to transport, has negligible boil-off but requires energy for cracking.
A study of the Australia-Japan corridor shows that shipping LH2 emits 0.3-0.5 kg CO2 per kg of hydrogen over 5,000 km, while ammonia shipping emits 0.1-0.3 kg CO2 per kg due to higher energy density. For MENA-Europe routes (3,000 km), emissions are proportionally lower but follow similar trends.
**Regional Production vs. Import Scenarios**
Comparing domestic renewable hydrogen production in Japan and Europe to imports reveals trade-offs. Japan, with limited land for renewables, may find imports cost-effective despite transport emissions. Australia’s solar and wind potential allows for low-emission hydrogen production, but liquefaction and shipping add 15-20% to the carbon footprint.
Europe’s domestic production from offshore wind could yield 1-2 kg CO2 per kg of hydrogen, while MENA imports (using solar PV) may add 0.5-1 kg CO2 from shipping and conversion. However, MENA’s lower renewable costs could offset emissions if clean energy powers all stages.
**Key Emission Drivers**
The primary emission sources in hydrogen trade are:
- Production method (grey vs. green hydrogen)
- Liquefaction or carrier conversion energy source
- Maritime transport distance and efficiency
- End-use cracking or dehydrogenation
A plain-text table summarizes emissions for two corridors:
| Corridor | Production Emissions (kg CO2/kg H2) | Liquefaction/Conversion (kg CO2/kg H2) | Transport (kg CO2/kg H2) | Total (kg CO2/kg H2) |
|------------------|-----------------------------------|--------------------------------------|-------------------------|---------------------|
| Australia-Japan | 0 (green) / 10 (grey) | 5-7 (LH2) / 2-3 (ammonia) | 0.3-0.5 (LH2) | 5.3-7.5 (LH2) |
| MENA-Europe | 0 (green) / 10 (grey) | 1.5-2 (ammonia) | 0.1-0.3 (ammonia) | 1.6-2.3 (ammonia) |
**Policy and Technology Implications**
To minimize emissions, hydrogen trade must prioritize:
- Renewable energy for liquefaction and conversion
- Shorter shipping routes or higher carrier efficiency
- Investment in low-emission cracking technologies
Countries like Japan and Germany are already incentivizing clean hydrogen imports, but certification systems must account for full lifecycle emissions. Meanwhile, advancements in electrolysis, ammonia cracking, and LOHC dehydrogenation could further reduce the carbon intensity of traded hydrogen.
In conclusion, while international hydrogen trade enables renewable resource sharing, its emissions depend heavily on production and transport choices. Regional production may be preferable where renewables are abundant, but imports can still offer climate benefits if supply chains are optimized. The Australia-Japan and MENA-Europe corridors illustrate the balance between resource availability and logistical emissions, underscoring the need for tailored solutions in the global hydrogen economy.