Before the COVID-19 pandemic, aviation accounted for 3.1% of global carbon emissions from fossil fuel combustion – roughly on par with the entire nation of Japan. Aviation is one of the most difficult to sectors of the economy decarbonize, but multiple pathways to reach net-zero by 2050 are possible, according to a new study.
The feat won’t be easy, involving some combination of behavior change to reduce demand for flying and investments in new and costly technologies.
“The more demand grows, and the more modest your energy efficiency improvements are, then the more you need to rely on sustainable aviation fuels and on carbon dioxide removals,” says study team member Candelaria Bergero, a graduate student at the University of California in Irvine.
Bergero and her colleagues assessed nine different scenarios for aviation to reach net-zero emissions by 2050, varying in the level of demand for air travel and freight, the energy intensity of aviation, and the carbon intensity of aviation.
If demand for air travel grows by 4% per year and energy efficiency improves by 1% per year – both in line with historical averages – then up to 19.8 exajoules of sustainable fuels would be required for the aviation sector to reach net-zero emissions, the researchers report in the journal Nature Sustainability.
Sustainable aviation fuels include synthetic fuels made with green hydrogen and carbon captured from the air, as well as biofuels from agriculture residues, trees, corn, food waste, and used cooking oil.
Producing biofuels for sustainable aviation could require as much as 1.2 million square miles of cropland, about one-fifth of the total cropland under cultivation today.
If people decide to fly less, holding increases in demand to 1% per year, while efforts to increase the energy efficiency of airplanes ramp up to achieve improvements of 4% per year, then net-zero aviation would require 3 exajoules of sustainable fuel.
That’s roughly the total amount of biofuels produced in 2019. (Of that, bio-based jet fuel amounted to just 0.005 exajoules.) So even an optimistic scenario would require a significant ramping up of biofuel production.
Airlines could increase energy efficiency with strategies such as gliding in for landings or changing flight paths to take better advantage of prevailing winds.
Contrails are responsible for two-thirds of aviation’s climate impact, so even if aviation fuel becomes climate-neutral there will still be a need to mitigate the warming effect of contrails. If air travel continues at similar levels as today, contrails would require up to 3.4 gigatons of carbon dioxide to be captured from the air and permanently stored for aviation to reach net-zero climate impact.
A heavy reliance on sustainable fuels and carbon capture to achieve net zero could be economically challenging, Bergero says. “Both are very expensive today.”
Although battery electric and hydrogen-based aircraft are under development, these have limited range, increasing the importance of sustainable fuels in net-zero pathways. “There has been a lot of hype and enthusiasm for these technologies, which is of course great, but these technologies would only help us decarbonize short-haul aviation,” says Bergero.
Governments could help ensure decarbonization of the aviation industry with policies to encourage development and deployment sustainable aviation fuels, as well as a tax on carbon that would decrease the relative cost of sustainable fuels.
“I also think it is very important that consumers demand clear and transparent standards for carbon credits, so that airlines don’t just offset their emissions with non-permanent and cheap carbon offsets,” Bergero says.
Source: Bergero C. et al. “Pathways to net-zero emissions from aviation.” Nature Sustainability 2023.
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