CANDELARIA BERGERO

The greenhouse gas emissions caused by our energy system threaten a sustainable future. To overcome this threat, we need to transition towards cleaner energy forms. We have to change nearly everything around us: from the way we heat our homes, to the ways we power our planes and produce our steel. My research focuses on how we can achieve this transition and on the environmental justice implications for people like you and me.

My passion is to establish a symbiotic relationship with our planet and with one another.

Pathways to net-zero emissions from aviation

2023

Photo by Philip Myrtorp on Unsplash

Nature sustainability

Candelaria Bergero, Greer Gosnell, Dolf Gielen, Seungwoo Kang, Morgan Bazilian, Steven Davis

DOI: 10.1038/s41893-022-01046-9

International climate goals imply reaching net-zero global carbon dioxide (CO₂) emissions by roughly mid-century (and net-zero greenhouse gas emissions by the end of the century). Among the most difficult emissions to avoid will be those from aviation given the industry’s need for energy-dense liquid fuels that lack commercially competitive substitutes and the difficult-to-abate non-CO₂ radiative forcing. Here we systematically assess pathways to net-zero emissions aviation. We find that ambitious reductions in demand for air transport and improvements in the energy efficiency of aircraft might avoid up to 61% (2.8 GtCO2 equivalent (GtCO₂eq)) and 27% (1.2 GtCO₂eq), respectively, of projected business-as-usual aviation emissions in 2050. However, further reductions will depend on replacing fossil jet fuel with large quantities of net-zero emissions biofuels or synthetic fuels (that is, 2.5–19.8 EJ of sustainable aviation fuels)—which may be substantially more expensive. Moreover, up to 3.4 GtCO₂eq may need to be removed from the atmosphere to compensate for non-CO₂ forcing for the sector to achieve net-zero radiative forcing. Our results may inform investments and priorities for innovation by highlighting plausible pathways to net-zero emissions aviation, including the relative potential and trade-offs of changes in behaviour, technology, energy sources and carbon equivalent removals.

a, Total global aviation demand (D) for BAU (orange), Industry projections (blue) and Ambitious (green) scenarios. b, Energy intensity of air transport (e) for the same scenarios. c, Carbon intensity of aviation energy (f) in gCO2 MJ⁻¹ for Carbon Intensive (red), Reduced fossil (blue) and Net-zero (green) scenarios. d, Carbon equivalent intensity (f) for aviation in gCO_2eq MJ⁻¹ based on a GWP100 for the same scenarios. e, Carbon dioxide emissions in GtCO₂ from fossil jet fuel burning by combining three carbon intensity scenarios (f) with three demand and energy intensity scenarios (BAU D with BAU e, Industry D with Industry e and Ambitious D with Ambitious e). f, Carbon-equivalent emissions in GtCO_2eq based on a GWP100 estimate based on Lee et al. Historical data (black) for each panel are shown for 1990–2021; projections are shown for 2022–2050. Panel a shows the breakdown of total demand by passenger and freight aviation. Panels e and f represent the emissions ranges for each group of demand and energy-intensity scenarios in combination with the different carbon-intensity scenarios. Panel f shows the historical breakdown between CO₂ and non-CO₂ emissions.

Each column represents a combination of demand and energy intensity (De), and each row represents a carbon-intensity trajectory (f). Each panel represents a demand and energy-intensity trajectory combined with a specific carbon intensity (Def). Colours for the headers represent low- (orange/red), medium- (blue) and high-ambition (green), for example, panel a represents the lowest ambition scenario with BAU demand and energy intensity and a carbon intensive fuel mix. Each bar within each panel represents a Kaya parameter: historical emissions in 2021 (maroon), increase in emissions based on projected demand (blue), decrease in emissions based on energy-intensity improvements (orange), potential further reductions due to changes in carbon intensity of energy (green) and carbon dioxide removals (CDR) needed to reach net-zero by 2050 (grey). The CDR grey bar is divided into two, representing the split between CO₂ and non-CO₂ equivalent emissions in each scenario.

a,b, SAF demand varies considerably for reduced fossil (a) and net-zero (b) pathways. Each solid line represents a combination of demand (D) and energy intensity (e); orange stands for BAU, blue for Industry projections and green for Ambitious pathways. The dashed horizontal grey line in the bottom shows total biofuel production worldwide in 2019, whereas the top dashed line shows the total global traditional use of biomass in the same year. For reference, in 2019, total global bioenergy use was almost 64 EJ while bio-jet fuel production was only 0.005 EJ.

a–f, Contours show costs of synthetic fuel (a,b), FT biofuels (c,d) and hydro-processed esters and fatty acids (e,f) based on key input costs and conversion efficiencies. The left three panels (a,c,e) include the cost for producing each fuel. The right three panels (b,d,f) represent the same costs as in the right panels plus what it would cost to remove from the atmosphere the carbon equivalent non-CO₂ emissions embedded in a liter of SAF for a GWP100 and an assumed cost of CDR of US$350 t⁻¹ CO₂ . For comparison, one of the dashed white lines in each left panel indicates the 2022 average cost of fossil jet fuel as of the end of May (US$0.80 l⁻¹), according to IATA’s Fuel Price Monitor. The other dashed white line represents upper-end costs from the literature.

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