(273g) Absolute Environmental Sustainability Assessment of Chemicals and Bridging Gaps to Becoming ‘Nature Positive’

‘Nature Positive by 2030’, ‘Net-Zero by 2050’...have been widely accepted as global goals for guiding decisions towards a healthier planet [1]. The chemical industry is one of the largest and most pervasive industries, with chemicals used in numerous applications including agriculture, medicine, food, and manufacturing. However, this industry has also caused significant and irreversible environmental impacts that have led to the urgent need for sustainability assessment and action. To this end, conventional sustainability assessment methods, such as life cycle assessment (LCA), provide relative sustainability metrics by comparing one system to another. However, these metrics are sensitive to the selection of the reference group. Alternatively, absolute environmental sustainability assessment (AESA) defines an absolute value - nature's carrying capacity, against which the environmental impacts of a system are compared [2].

In this work, we extended the multiscale method based on the Techno-ecological synergy (TES) framework for AESA [3]. We selected four major chemicals - ammonia, methanol, ethylene, and benzene - and focused on carbon dioxide emissions to assess their AES metrics at the country and global levels. We compared different sharing principles, including emissions, gross value added (GVA), and historical accumulative emissions, to gain insights into the responsibility that each stakeholder should take in achieving sustainable global goals. We also compared our multiscale AESA method with the benchmark method based on the planetary boundary (PB) framework, highlighting the limitations of the latter. The AES metric is quantified by comparing a system’s or product’s environmental impacts versus ecological thresholds. We used Ecoinvent 3.8 life cycle inventory database to estimate the life cycle emission of these four chemicals in nine major producer countries. While most AESA research is conducted at the global scale, we argue that results should be conducted at smaller scales to guide stakeholders towards sustainability goals and we explored how to do it. After quantifying gaps for these chemicals to becoming ‘nature positive’, we looked into different ‘green pathways’ to explore the potential opportunities in low carbon transition of the chemical industry. For instance, using renewable energies from biomass, solar, wind; installing carbon capture and storage units; reforestations and restore ecosystems, etc.

The planetary boundary framework defines nine key earth system processes [4]. Each earth system process has a quantitative boundary at global or subglobal scale which can be referred to ecological threshold. In PB-based AESA methods, boundaries will be directly downscaled to a process or product system [5-7] which makes the result highly dependent on the choice of sharing principles. Issues above could provide misleading results as spatial heterogeneity is ignored. Our TES framework avoids these issues by quantifying ecosystem services (ES) through biophysical models, providing high geographical resolutions for ecological threshold quantification. Due to the nested character of ecosystems, ESs are quantified from small to large scales. We applied a 2-scale TES framework, including national and global scales, to reflect stakeholder capabilities to take in CO2 emissions sustainably. Public and private ownership of ESs are considered during allocation to avoid introducing subjectiveness and also to encourage stakeholders to restore ecosystems. Ecological thresholds at global scale will be partially allocated to specific products by certain sharing principles such as gross value added, population, etc. We compared different sharing principles that are commonly used. Considering the fact that countries began industrialization at different times and at different levels of development, countries like united states and European union countries have emitted considerable amount of CO2 for decades while countries like China, India have a shorter high emission time range. From the egalitarianism aspect, accumulative historical emission should be considered and we explored a novel criteria based on it. Applying the same method, we extended the scope to whole the chemical industry using chemicals and materials industry model.

Results show large variation of transgression levels among different countries, some stay within ecological thresholds while some not which are not reflected from other studies in this topic. When these regional transgression levels be scaled up to global level, the variations will be averaged. In conclusion, this work contributes to the urgent need for sustainability assessment and action. The multiscale TES-based method used in this work provides targeted insights for stakeholders to transition towards a low-carbon chemical industry, avoiding the limitations of the PB framework.

1. Global Goal for nature. https://www.naturepositive.org/. Accessed: 2022-12-13.

2. Bjørn, Anders, Katherine Richardson, and Michael Zwicky Hauschild. "A framework for development and communication of absolute environmental sustainability assessment methods." Journal of Industrial Ecology 23.4 (2019): 838-854.

3. Xue, Ying, and Bhavik R. Bakshi. "Metrics for a nature-positive world: A multiscale approach for absolute environmental sustainability assessment." Science of The Total Environment 846 (2022): 157373.

4. Rockström, Johan, et al. "A safe operating space for humanity." nature 461.7263 (2009): 472-475.

5. D’Angelo, Sebastiano Carlo, et al. "Planetary boundaries analysis of low-carbon ammonia production routes." ACS Sustainable Chemistry & Engineering 9.29 (2021): 9740-9749.

6. González-Garay, Andrés, et al. "Plant-to-planet analysis of CO 2-based methanol processes." Energy & Environmental Science 12.12 (2019): 3425-3436.

7. Ryberg, Morten W., et al. "How to bring absolute sustainability into decision-making: an industry case study using a planetary boundary-based methodology." Science of the Total Environment 634 (2018): 1406-1416.