# Current aviation roadmaps are not within planetary boundaries

Bastien Païs, Alexandre Gondran, Lorie Hamelin, Florian Simatos

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Bastien Païs, Alexandre Gondran, Lorie Hamelin, Florian Simatos. Current aviation roadmaps are not within planetary boundaries. SETAC Europe 35th Annual Meeting, SETAC Europe, May 2025, Vienne, Austria. hal-05316781

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Submitted on 15 Oct 2025

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# Current aviation roadmaps are not within planetary boundaries

Bastien Païs¹,²,³, Alexandre Gondran⁴, Lorie Hamelin⁵, Florian Simatos¹

¹ ISAE-SUPAERO, France

² ADEME, France

³ Institute for Sustainable Aviation, France

³ Toulouse Biotechnology Institute, France

⁴ ENAC, France

E-mail contact: bastien.pais@isae.fr

## 1. Introduction

The aviation sector is a significant contributor to global warming, accounting for almost 4% of effective radiative forcing [1]. To assess its climate footprint over time, the sector and its various stakeholders have developed numerous prospective scenarios (e.g. [2][3]) incorporating different assumptions about traffic growth, fleet renewal, the introduction of new technologies, and the use of alternative fuels. The latter is the primary climate mitigation lever being considered.

However, these scenarios and the various technical solutions they propose are evaluated primarily through the prism of climate, neglecting broader environmental impacts. In fact, biofuels imply an increased biomass demand and hence impacts on land-system change, water use, and nitrogen and phosphorus biogeochemical cycles. Similarly, liquid hydrogen and electrofuels heavily rely on increased electricity production, which has impacts far beyond climate, for both current and decarbonized power sources.

The Planetary Boundaries (PBs) framework [4], scaled down to the sectorial level, allows for Absolute Environmental Sustainability Assessment (AESA) of these scenarios.

The literature about the operationalization of PB at smaller scales has undergone significant development in recent times. Leveraging recently developed tools and methodologies [5][6][7], this study introduces methodological and conceptual advancements to facilitate dynamic and prospective AESAs and present applications to aviation prospective scenarios.

## 2. Materials and Methods

### 2.1. Prospective scenarios and environmental impacts

The prospective assessment of aviation's impacts requires both prospective scenarios of the sector's energy demand and prospective emission factors associated with the production and use of this energy. Here, a set of 217 illustrative scenarios representative of the wide range of scenarios proposed by a diversity of stakeholders (industrial, academic and institutional) have been generated.

Technologies' emission factors must be prospective to conduct a coherent study. Even though the focus here is on the aviation sector, its transition scenarios are part of a global transition scenario. To ensure alignment of our aviation scenarios with the entire technosphere, the *premise* tool [6] was used to incorporate the evolution of current and emerging technologies' technical and environmental performances, considering different Integrated Assessment Models (REMIND and IMAGE) and global scenarios (SSP1-RCP1.9, SSP2-RCP2.6, and SSP2-NPI).

### 2.2. Linking prospective scenarios, environmental impacts and planetary boundaries

Our approach links the prospective scenarios, their environmental impacts, and the PB framework using the PB-LCIA methodology [5], which we adapted to the scope of our study. Among others, as we aim to assess the impacts of dynamic scenarios where emissions vary from year to year, using existing PB-LCIA characterization factors for climate change and biosphere integrity would lead to temporal inconsistency. Therefore, we rely on the Bern simplified carbon model to dynamically evaluate the impact on these two key planetary boundaries.
## 2.3. Comparing prospective impacts to downscaled planetary boundaries

To conduct an AESA, it is essential to compare the impacts of the studied activity to a reference of absolute environmental sustainability. This reference can be derived from the PB framework. To achieve this, a downscaling step is necessary to move from the global scale to the activity scale.

Heide et al. [7] developed a method based on the concept of sufficientarianism (ensuring everyone has enough – method called FHN for Fulfilment of Humand Needs). The method relies on the notion of "safe and just" reference countries. This publication serves as a proof of concept with some limitations (application to certain PB only due to lack of data), which we addressed through our approach, using other sources of data concerning the PB footprints of reference countries.

## 3. Results and Discussion

<figure><img src="image_2.png" /><figcaption>**Figure 1 - AESAs of 2022 aviation and two potential 2050 aviations futures (out of 217 studied). The SoSOS (=1) is represented in dotted line, SoSOS exceedance is illustrated in red. The applied downscaling considers the FHN method. PPM=Atmospheric CO₂ concentration, RF=Energy imbalance at top-of-atmosphere, O₃=Stratospheric ozone depletion, BII=Biosphere integrity, LSC=Land-system change, FWU=Freshwater use, N=Nitrogen cycle, P=Phosphorus cycle**</figcaption></figure>

Historical aviation (1940-2022) was shown to already exceeds its FHN-based share of safe operating space for climate change, biosphere integrity, and nitrogen cycle (Figure 1). Scenarios using alternative fuels have a lower climate impact than the 100% fossil fuel scenario, but generate new potential environmental problems, such as the disruption of the phosphorus cycle. Among the 217 scenarios studied, none can be classified as absolutely sustainable.

## 4. Conclusions

By using new tools and developing an appropriate methodology, our work highlights the potential and the limits of alternatives fuels to reduce the environmental impacts of aviation. It also shows the absolute environmental unsustainability of the aviation sector in the years to come, within the context of a FHN-based downscaling. Furthermore, the development of this methodology opens up the possibility of conducting prospective and dynamic AESAs for other sectors of activity, enabling the anticipation of sustainability issues as well as the displacement of environmental problems in a context of climate mitigation.

## 5. References

[1] Delbecq et al. 2023. Sustainable aviation in the context of the Paris Agreement: A review of prospective scenarios and their technological mitigation levers. *Progress in Aerospace Sciences* 141: 100920.

[2] Dray et al. 2022. Cost and Emissions Pathways towards Net-Zero Climate Impacts in Aviation. *Nature Climate Change* 12: 956-62.

[3] Bergero et al. 2023. Pathways to Net-Zero Emissions from Aviation. *Nature Sustainability*: 1-11.

[4] Richardson et al. 2023. Earth beyond Six of Nine Planetary Boundaries. *Science Advances* 9: eadh2458.

[5] Ryberg et al. 2018. Development of a Life-Cycle Impact Assessment Methodology Linked to the Planetary Boundaries Framework. *Ecological Indicators* 88: 250-62.

[6] Sacchi, R. et al. 2022. Prospective EnvironMental Impact asSEment (premise): A streamlined approach to producing databases for prospective life cycle assessment using integrated assessment model. *Renewable and Sustainable Energy Reviews* 160: 112311.

[7] Heide et al. 2023. Reflecting the importance of human needs fulfilment in absolute sustainability assessments: Development of a sharing principle. *Journal of Industrial Ecology* 27: 1141-1164.