Editing IPCC:AR6/WGIII/Chapter-11 (section)

=== 11.3.2 Material Efficiency ===

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Material efficiency ( ''ME'' ) – the delivery of goods and services with less material – is increasingly seen as an important strategy for reducing GHG emissions in industry ( [[#IEA--2017|IEA 2017]] , 2019b). Options to improve ''ME'' exist at every stage in the lifecycle of materials and products, as shown in Figure 11.7. This includes: designing products which are lighter, optimising to maintain the end-use service while minimising material use, designing for circular principles (i.e., longer life, reusability, repairability, and ease of high-quality recycling); pushing manufacturing and fabrication process to use materials and energy more efficiently and recover material wastes; increasing the capacity, intensity of use, and lifetimes of product in use; improving the recovery of materials at the end of life, through improved remanufacturing, reuse and recycling processes. For more specific examples see [[#Allwood--2012|Allwood et al. (2012)]] ; [[#Lovins--2018|Lovins (2018)]] ; [[#Hertwich--2019|Hertwich et al. (2019)]] ; [[#Scott--2019|Scott et al. (2019)]] ; and [[#Rissman--2020|Rissman et al. (2020)]] .

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[[File:1642ea8c765f2b393363e9da10315dc9 IPCC_AR6_WGIII_Figure_11_7.png]]

'''Figure 11.7 | Material efficiency (''' ''ME'' ''') strategies across the value chain.''' Source: derived from strategies in [[#Allwood--2012|Allwood et al. (2012)]] .

''ME'' provides plentiful options to reduce emissions, yet because interventions are dispersed across supply chains and span many different stakeholders, this makes assessing mitigation potentials and costs more challenging. For this reason, ''ME'' interventions have traditionally been under-represented in climate change scenario modelling and integrated assessment models (IAMs) ( [[#Grubler--2018|Grubler et al. 2018]] ; [[#Allwood--2018|Allwood 2018]] ). However, two advances in the modelling of materials flows have underpinned the recent emergence of ''ME'' options being included in climate scenario modelling.

Firstly, over many years, the academic community has built up detailed global material-flow maps of the processing steps involved in making energy-intensive materials. Some prominent recent examples include: steel ( [[#Gonzalez%20Hernandez--2018b|Gonzalez Hernandez et al. 2018b]] ), pulp and paper ( [[#Van%20Ewijk--2018|Van Ewijk et al. 2018]] ), petrochemicals ( [[#Levi--2018|Levi and Cullen 2018]] ). In addition, material-flow maps at the regional and sectoral levels have flourished, for example: steel ( [[#Serrenho--2016|Serrenho et al. 2016]] ) and cement ( [[#Shanks--2019|Shanks et al. 2019]] ) in the UK; automotive sheet-metal ( [[#Horton--2019|Horton et al. 2019]] ); and steel-powder applications ( [[#Azevedo--2018|Azevedo et al. 2018]] ). The detailed and transparent physical mapping of material supply chains in this manner enables ''ME'' interventions to be traced back to where emissions are released, and allows these options to be compared against decarbonisation and traditional energy efficiency measures ( [[#Levi--2018|Levi and Cullen 2018]] ). For example, a recent analysis by [[#Hertwich--2019|Hertwich et al. (2019)]] makes the link between ''ME'' strategies and reducing GHG emissions in buildings, vehicles and electronics, while [[#Gonzalez%20Hernandez--2018a|Gonzalez Hernandez et al. (2018a)]] examines leveraging ''ME'' as a climate strategy in European Union (EU) policy. Research to explore the combined analysis of materials and energy, using exergy analysis (for steel: [[#Gonzalez%20Hernandez--2018b|Gonzalez Hernandez et al. 2018b]] ) allows promising comparisons across industrial sectors.

Secondly, many ''ME'' interventions result in immediate GHG emissions savings (short-term), for example, light-weighting products, reusing today’s product components, and improving manufacturing yields. Yet, for other ''ME'' actions emissions savings are delayed temporally (long-term). For example, designing a product for future reuse, or with a longer life, only reaps emissions savings at the end of the product life, when emissions for a replacement product are avoided. Many durable products have long lifetimes (cars &gt;10 years, buildings &gt;40 years) which requires dynamic modelling of material stocks, over time, to enable these actions to be included in scenario modelling activities. Consequently, much effort has been invested recently to model material stocks in use, to estimate their lifetimes, and anticipate the future waste and replenishment materials to maintain existing stocks and grow the material stock base. Dynamic material models have been applied to material and product sectors, at the country and global level. These include, for example: vehicles stocks in the UK ( [[#Serrenho--2017|Serrenho et al. 2017]] ; [[#Craglia--2020|Craglia and Cullen 2020]] ) and in China ( [[#Liu--2020|Liu et al. 2020]] ); buildings stocks in the UK ( [[#Cabrera%20Serrenho--2019|Cabrera Serrenho et al. 2019]] ), China ( [[#Hong--2016|Hong et al. 2016]] ; [[#Cao--2018|Cao et al. 2018]] , 2019) and the European Union ( [[#Sandberg--2016|Sandberg et al. 2016]] ); electronic equipment in Switzerland ( [[#Thiébaud--2017|Thiébaud et al. 2017]] ); specific material stocks, such as cement ( [[#Cao--2020|Cao et al. 2020]] , 2017), construction materials ( [[#Sverdrup--2017|Sverdrup et al. 2017]] ; [[#Habert--2020|Habert et al. 2020]] ), plastics ( [[#Geyer--2017|Geyer et al. 2017]] ), copper ( [[#Daehn--2017|Daehn et al. 2017]] ), and all metals ( [[#Elshkaki--2018|Elshkaki et al. 2018]] ); all materials in China ( [[#Jiang--2019|Jiang et al. 2019]] ), Switzerland ( [[#Heeren--2019|Heeren and Hellweg 2019]] ) and the world ( [[#Krausmann--2017|Krausmann et al. 2017]] ).

These two advances in the knowledge base have allowed the initial inclusion of some ''ME'' strategies in energy and climate change scenario models. The International Energy Agency (IEA) first created a ''ME'' scenario (MES) in 2015, with an estimated 17% reduction in industrial energy demand in 2040 ( [[#IEA--2015|IEA 2015]] ). The World Energy Outlook report includes a dedicated sub-chapter with calculations explicitly on industrial material efficiency ( [[#IEA--2019c|IEA 2019c]] ). They also include ''ME'' options in their modelling frameworks and reporting, for example for petrochemicals ( [[#IEA--2018a|IEA 2018a]] ), and in the Material Efficiency in Clean Energy Transitions report ( [[#IEA--2019b|IEA 2019b]] ). In [[#Grubler--2018|Grubler et al. (2018)]] 1.5°C Low Energy Demand (LED) scenario, global material output decreases by 20% from today, by 2050, with one-third due to dematerialisation, and two-thirds due to ''ME'' , resulting in significant emissions savings. Material Economics’ analysis of Industrial Transformation 2050 ( [[#Material%20Economics--2019|Material Economics 2019]] ), found that resource efficiency and circular economy measures (i.e., ''ME'' ) could almost halve the 530 MtCO 2 yr –1 emitted by the basic materials sectors in the EU by 2050. Finally, the Emissions Gap Report, [[#UNEP--2019|UNEP (2019)]] includes an assessment of potential material efficiency savings in residential buildings and cars.

Clearly, more work is required to fully integrate ''ME'' strategies into mainstream climate change models and future scenarios. Efforts are focused on endogenising ''ME'' strategies within climate change modelling, assessing the synergies and trade-offs which exist between energy efficiency and ''ME'' interventions, and building up data for the assessment of emissions saved and the cost of mitigation from real ''ME'' actions. This requires analysts to work in cross-disciplinary teams and to engage with stakeholders from across the full breadth of material supply chains. Efforts should be prioritised to foster engagement between the IAM community and emerging ''ME'' models based in the Life Cycle Assessment, Resource Efficiency, and Industrial Ecology communities (see also [[#Sharmina--2021|Sharmina et al. 2021]] ).

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