The Role of Airplanes in Global CO2 Emissions and Their Future Decarbonization Pathways

According to recent data, airplanes contribute a considerable amount to global CO2 emissions. In 2020, petroleum, which is predominantly used as aviation fuel, accounted for 10.3 billion metric tons of CO2 out of a global total of about 32.3 billion metric tons. This figure represents 3.2% of the total fossil fuel emissions. The challenge lies in decarbonizing this sector, as jet fuel remains largely unreplaced by electricity-driven alternatives.

Replacements for Jet Fuel: Hydrogen and Renewable Energy

Currently, the process of producing jet fuel from water using renewable electricity to separate the hydrogen from oxygen and then recombine it into jet fuel is the most promising path for decarbonization. This process, known as electrolysis, has been proven by multiple companies, and it has received approval from the U.S. Department of Energy for military aircraft usage. When there is an excess of wind or solar power over traditional fossil fuel sources, factories can be built to convert this excess into hydrogen. This hydrogen can then be converted into hydrocarbon or ammonia before being transported and used as jet fuel.

Hydrogen-Fueled Aviation

While there is excitement about the direct use of hydrogen, many projects plan to convert hydrogen into hydrocarbons or ammonia before it leaves the plant. This is because direct use of hydrogen in aviation involves significant technological and infrastructural challenges. For instance, hydrogen tanks must be ultra-durable and lightweight to meet aviation safety and performance standards. Additionally, the production, storage, and transportation of hydrogen must align with existing fuel distribution infrastructure.

The Future of Aviation and Renewable Energy

For the production of hydrogen to become economically viable on a large scale, the wind and solar energy mix needs to become significantly larger. While there is a debate about how much renewable energy is required, a commonly cited figure is around 60% of the total supply. This renewable energy mix would provide the necessary excess generation to produce hydrogen. As the renewable energy sector continues to grow, the price of electricity will drop, making renewable jet fuel a more economical alternative to traditional fossil fuels.

Electric Aircraft as a Partial Solution

Electric aircraft are likely to replace certain existing propeller aircraft, but they will not suffice for the more advanced engines used in commercial and military aviation. The benefits of electric propulsion in smaller aircraft include lower operating costs and quieter operations, making it an attractive solution for close-range flights and cargo transportation.

Conclusion

The decarbonization of aviation is a complex challenge that requires a multifaceted approach. While direct hydrogen use in aviation remains promising, the reality is that most projects are planning to produce renewable hydrocarbons or ammonia from hydrogen. This approach aligns with existing aerospace standards and infrastructure. As the renewable energy sector continues to expand, affordable and sustainable alternatives to jet fuel will become more feasible, paving the way for a greener sky.