Climate neutrality is becoming a core long-term competitiveness factor within the aviation industry, as demonstrated by the several innovations and targets set within that sector, prior to and especially after the COVID-19 crisis. Ambitious timelines are set, involving important investment decisions to be taken in a 5-years horizon time. Here, we provide an in-depth review of alternative energy sourcing technologies for aviation revealed to date, which we classified into three main categories, namely liquid fuels (biofuels, electrofuels), electric aviation (all electric and hybrid), and carbon-free options (hydrogen-based, solar-powered). For liquid fuels, 10 pathways were reviewed, for which we supply the detailed process flow picturing all input, output, and co-products generated. The market uptake and use of these co-products were also investigated, along with the overall international regulations and targets for future aviation. As most of the inventoried pathways require hydrogen, we further reviewed six existing and emerging carbon-free hydrogen production technologies. Our review also details the five key battery technologies available (lithium-ion, advanced lithium-ion, solid-state battery, lithium-sulfur, lithium-air) for aviation, as well as the possible configuration schemes for electric propulsion (parallel electric hybrid, series electric hybrid, all electric, partial turboelectric and full turboelectric) and reflects upon the inclusion of hydrogen-powered fuel cells with these configurations. Our review studied these three categories of energy sourcing pathways as modular technologies, yet these still have to be used in a hybridized fashion with conventional fossil-based kerosene. This is among others due to an aromatics content below the standardized requirements for biofuels and electrofuels, to a too low energy storage capacity in the case of batteries, or a sub-optimal gas turbine engine in the case of cryogenic hydrogen. Yet, we found that the latter was the only available option, based on the current and emerging technologies reviewed, for a long-range aviation completely decoupled of fossil carbon. The various challenges and opportunities associated with all these technologies are summarized in this study.

The removal of additional carbon dioxide from the atmosphere is indispensable for controlling global warming. This study proposed the concept of ‘biopump’, as plants capable of significantly transferring carbon into the soil. The Carbon Storage in Arable land and Anthropogenic Products (CSAAP) relates to the cultivation of ‘biopumps’ on marginal arable lands poor in soil organic carbon (SOC) and their conversion into long-lived anthropogenic products. Based on a list of twenty-seven biopumps assembled from a literature review, this study proposed a method for the regional prioritization of biopumps, considering among others their ability to increase SOC and adaptation. A list with eight woody and eight herbaceous biopumps was recommended for France. To illustrate the potential of the CSAAP strategy for products encompassing a variety of lifetimes, carbon flows, from biopump cultivation to biomaterial manufacturing and end-of-life, were tracked in time to calculate their influence on global mean temperature change. An illustration was performed on the basis of a French case study, where Miscanthus is grown on spatially identified marginal lands quantified as 11,187- 24,007 km2. Planting biopumps on these lands could increase by 0.23 to 0.49 Mt carbon stocked as SOC annually, which represents 0.19%- 0.41% of the annual French carbon budget during 2015-2018. If the carbon contained in the biomass is indefinitely kept in anthropogenic products, it could represent 13.07% of the same carbon budget. We concluded that biopumps could induce negative emission by 2100, with efficiency strongly depending upon carbon’ residence time in the anthroposphere.