Extracting and processing raw materials into products for industry is a substantial source of CO2 emissions, yet this process often lacks granular detail in many integrated assessment models (IAMs). To broaden the space of climate change mitigation options and include circular economy and material efficiency measures, researchers at the International Institute for Applied Systems Analysis (IIASA) have developed the MESSAGEix-Materials module. This open-source addition to the MESSAGEix-GLOBIOM IAM framework represents material flows and stocks for the most energy and emissions-intensive industries: aluminum, iron and steel, cement, and petrochemicals.
The MESSAGEix-Materials module enables a more comprehensive assessment of industry decarbonization pathways under various climate targets. By integrating material flow analysis with energy system modeling, this new capability connects physical material stocks and flows to the associated energy use and greenhouse gas (GHG) emissions. This allows IAM scenario analysis to capture interactions between material demand, energy systems, and climate change mitigation strategies centered on the circular economy and material efficiency.
Integrating Material Flow Analysis and Energy System Modeling
Conventional energy system models like MESSAGEix have typically focused on energy commodity flows and the resulting GHG emissions. However, to address material-oriented mitigation strategies, it becomes necessary to expand the scope towards fully covering material cycles and the dynamics of material stocks.
The MESSAGEix-Materials module draws on the principles of material flow analysis (MFA), which accounts for all material inputs, outputs, and stocks within a defined system boundary. This mass balance approach ensures that all material flows are traced, from raw material extraction to product manufacturing, use, and end-of-life waste management.
By combining MFA with the linear programming optimization of the MESSAGEix energy system model, the researchers have created a unique modeling framework. This allows for a more granular representation of industrial production processes, their associated energy requirements, and the resulting emissions—all while maintaining the broader systems perspective of an IAM.
Sector-Specific Representations
The MESSAGEix-Materials module focuses on the most energy and emissions-intensive industries:
Iron and Steel: Representing both the dominant blast furnace-basic oxygen furnace (BF-BOF) route and the competing direct reduction iron-electric arc furnace (DRI-EAF) process. The model incorporates low-carbon options like carbon capture and storage (CCS), hydrogen direct reduction, and biomass use.
Aluminum: Modeling the energy-intensive smelting process, with a choice between the more efficient pre-bake and the older Soderberg technologies. Secondary aluminum production from scrap is also included.
Cement: Capturing the cement clinker production via dry and wet kiln processes, as well as the option to deploy CCS to address process emissions from limestone calcination.
Petrochemicals: Providing a detailed representation of refining, steam cracking, and other conversion processes to produce key chemicals like ammonia, methanol, and high-value chemicals (e.g., ethylene, propylene, BTX).
Within each industry, the module tracks material flows at various stages—from raw material extraction, to intermediate processing, to final product manufacturing and end-of-life waste management. This level of granularity allows the model to assess the potential of circular economy strategies like recycling, as well as the energy and emissions implications of shifting production technologies.
Modeling Material Demand and Stocks
The MESSAGEix-Materials module determines material demand through a combination of endogenous and exogenous approaches. For the power sector, material stocks and flows are calculated endogenously based on the installed capacities of electricity generation technologies and their associated material intensities.
In contrast, material demands for other end-use sectors are projected exogenously using GDP-based econometric relationships. While this simplifies the modeling of material flows outside the power sector, the ultimate goal is to expand the endogenous coverage of material demand drivers, such as by linking to models of the buildings, transportation, and other key end-use sectors.
By representing the accumulation and retirement of material stocks, the model can also evaluate the impact of climate policies on the material requirements for infrastructure development and the associated energy use and emissions. For example, the increased electrification of the energy system under stringent climate targets leads to a significant rise in the demand for materials like steel, cement, and aluminum for power generation and grid expansion.
Insights from Scenario Analysis
Utilizing the enhanced granularity of the MESSAGEix-Materials module, researchers have generated detailed industry decarbonization pathways under a 2°C climate stabilization scenario. Some key insights include:
- The iron and steel sector contributes 6% of the total industry emissions reductions by 2070, driven by the scaled-up use of electric arc furnaces, hydrogen direct reduction, and carbon capture in blast furnaces.
- In the cement industry, carbon capture and storage (CCS) plays a crucial role, capturing 1.4 GtCO2 annually by 2070 and enabling a 46% share of electricity in cement production.
- The chemical industry shifts its methanol feedstock from fossil fuels to biomass with CCS, leading to net-negative emissions of 2.5 GtCO2 in 2070.
These technology-rich insights highlight the value of integrating material flow analysis within IAMs to better understand the challenges and opportunities in decarbonizing energy-intensive industries. The MESSAGEix-Materials module provides a flexible, open-source platform to explore the synergies between material strategies and climate change mitigation.
Expanding the Scope of IAMs
The development of MESSAGEix-Materials represents a significant advancement in integrated assessment modeling. By bridging the gap between energy system optimization and material flow analysis, this new capability enables IAMs to capture a broader range of mitigation options, including circular economy measures, material efficiency, and the implications of securing decent living standards.
As the module continues to evolve, future plans include expanding the representation of material stocks and flows beyond the power sector, incorporating additional energy-intensive industries, and exploring synergies between material strategies and other demand-side interventions. This will further strengthen the ability of IAMs to inform policymakers and industry on the optimal pathways for a sustainable, low-carbon future.
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