An anthropocene-framed transdisciplinary dialog at the chemistry-energy nexus

Abstract

At the energy-chemistry nexus, key molecules include carbon dioxide (CO₂), hydrogen (H₂), methane (CH₄), and ammonia (NH₃). The position of these four molecules and that of the more general family of synthetic macromolecular polymer blends (found in plastics) were cross-analyzed with the planetary boundary framework, and as part of five scientific policy roadmaps for the energy transition. According to the scenarios considered, the use of some of these molecular substances will be drastically modified in the coming years. Ammonia, which is currently almost exclusively synthesized as feedstock for the fertilizer industry, is envisioned as a future carbon-free energy vector. "Green hydrogen" is central to many projected decarbonized chemical processes. Carbon dioxide is forecast to shift from an unavoidable byproduct to a valuable feedstock for the production of carbon-based compounds. In this context, we believe that interdisciplinary elements from history, economics and anthropology are relevant to any attempted cross-analysis. Distinctive and crucial insights drawn from elements of humanities and social sciences have led us to formulate or re-raise open questions and possible blind-spots in main roadmaps, which were developed to guide, inter alia, chemical research toward the energy transition. We consider that these open questions are not sufficiently addressed in the academic arena around chemical research. Nevertheless, they are relevant to our understanding of the current planetary crisis, and to our capacity to properly assess the potential and limitations of chemical research addressing it. This academic perspective was written to share this understanding with the broader academic community. This work is intended not only as a call for a larger interdisciplinary method, to develop a sounder scientific approach to broader scenarios, but also - and perhaps mostly - as a call for the development of radically transdisciplinary routes of research. As scientists with different backgrounds, specialized in different disciplines and actively involved in contributing to shape solutions by means of our research, we bear ethical responsibility for the consequences of our acts, which often lead to consequences well beyond our discipline. Do our research and the knowledge it produces respond, perpetuate or even aggravate the problems encountered by society?

Fig. 1. The four molecules (CO₂, H₂, CH₄ and NH₃) and plastic polymers, chosen here as illustrative molecular substances sitting at the crux of the chemistry-energy nexus. For each of these substances, are reported: their current annual global production (in 2022), and the main Earth system processes with which they interact. In the case of dihydrogen, the shift in affected Earth system processes entailed by a shift towards production of “green hydrogen” (see Scheme 1 for definition) is materialized by an arrow. The current level of transgression of each planetary boundary estimated in literature is represented by its color, according to the caption at the bottom of the figure. Finally, current mode of production, main usage, and issues associated with end-of-life considerations are described in the blue boxes. More details in text and in ESI, Table SI-3.

Fig. 2. Production (left) and utilization (right) of H₂ in 2022, according to IEA. “Other sources” in the H₂ production panel include oil (0.5%), fossil fuels coupled to CCUS (0.6%), and water electrolysis (0.1%). “Other usage” in the H₂ utilization panel is mostly linked to the iron and steel industry (DRI, Direct Reduced Iron).

Scheme 1. Simplified chemical reactions (only one possible representative reaction is shown) associated with current fossil-based and projected hydrogen syntheses, with CO₂ emissions decreasing top to bottom and the corresponding “color” scheme used in literature. WGSR: water–gas shift reaction. CCS: carbon capture and storage.

Fig. 3. Left: annual (brown bars) and cumulative (blue line) global plastic production between 1950 and 2019 (data by OurWorldinData, Licence CC-BY). Right: comparison between the mass of animals (pink), trees & shrubs (green), plastic (blue), and building & infrastructure (gray). The areas of the squares are proportional to the total mass estimated for each group. The red dot in the “Animals” square represents at scale the mass of all human beings (ca. 0.06 Gt of carbon). Assumptions in mass accounting made in different studies explain the differences in absolute numbers between the left and right parts of the figure; the overall message remains the same in the two parts of the figure, with respect to the general trend discussed here.

Fig. 4. Upper panel: schematic representation of current fossil-based and projected ammonia synthesis processes with decreasing CO₂ emissions (top to bottom) and respective ammonia “color”. The CO₂ reported is only the stoichiometric quantity. See Scheme 1 for hydrogen syntheses. Since in ammonia plants, on-site hydrogen production is integrated with ammonia synthesis, the two hydrogen routes in Scheme 1 and here differ. Lower panel: differences between stoichiometric quantity (blue) and additional process-related CO₂ emissions (other colors) expressed in tCO₂/tNH₃ in modern optimized methane-powered Haber–Bosch processes for gray ammonia, leading to overall eqn (1) (see more on eqn (1) in Scheme SI-1†).

Fig. 5. The 2024 EuChemS periodic table of elements depicts element sustainability and causes of concern for future availability, including increased use and production from conflict resources, and impact on Earth system processes (“Serious global problems through overuse”). CC-BY-ND licence.

Fig. 6. Annual baseline water stress. Source: WRI (2019). Licence Creative Commons Attribution 4.0 International (CC by 4.0).

Fig. 7. Top: Evolution of world population over time (historical data) and projected world population without the development of the Haber–Bosch process, adapted from J. W. Erisman, et al. Right: the Food Hunger Map provided by the Food and Agricultural Organization of the United Nations. Global data make a clear causality link between the use of fertilizers and a growing population, but inequalities in access to food remain nonetheless. If ammonia really does feed “half of the world”, which half would that be?

Fig. 8. SW (stabilize the world) scenario for the projected evolution of population (blue line), pollution (orange line), food per capita (red line), non-renewable resources (green line), ecological footprint (brown line), human welfare (pink line), industrial output (gray line), and death rate (black line), and comparison with corresponding empirical data (dots), adapted from Herrington and Meadows. SW is referred as the sustainable model: indicators are stabilized on the long-term thanks to meaningful policy changes. Data for three other scenarios (Business As Usual and Comprehensive Technology) are available in ESI, Section SI-6 and Fig. SI-4.