Improve Steel Production involves replacing the use of fossil fuels in making steel from iron ore with electrolytic hydrogen and clean electricity. Doing so could reduce emissions from steel production by more than 90%. Although the necessary technologies exist, adoption has been very limited, with the major barriers being the cost of clean electricity and the availability of suitable iron ore. Other strategies for reducing the emissions from steel production typically rely on bioenergy sources or carbon capture and storage (CCS), which have limited potential to reduce emissions. As demand for steel grows globally, new policies are needed to increase market demand for low-emissions steel. Given the lack of improved steel facilities and supportive policies today, we will “Keep Watching” this solution.
Based on our analysis, Improve Steel Production using H2-DRI-EAF powered by clean electricity has the potential to significantly reduce emissions. However, while the individual technologies for H2-DRI-EAF are mature and their combined use has been piloted, the process has not yet been adopted in a meaningful way. We will “Keep Watching” this solution, but it is not ready for widespread adoption.
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | No |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | Yes |
| Impact | Is it big enough to matter? | Yes |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
Currently, making steel from iron ore relies heavily on coal and other fossil fuels to provide heat and reducing agents (chemicals that remove oxygen from iron ore). Improve Steel Production refers to using electric heat and hydrogen produced by electrolysis to reduce the iron ore (H2-DRI) and electric arc furnaces (EAF) to melt the resulting iron and alloy it with carbon to make steel. The solution also requires the electricity used in these processes to include significant renewable energy or other low-carbon generation. The output is varying grades of steel with different degrees of hardness and brittleness determined by slight variations in carbon content. This solution does not include processes that rely on bioenergy or CCS, since the emissions from burning bioenergy contribute to climate change and CCS is not an effective climate solution.
Replacing fossil fuels in steelmaking with H2-DRI-EAF that uses electrolytic hydrogen and where all electricity comes from relatively clean sources results in significantly reduced emissions. Steel made today using fossil fuels for heat and as a reducing agent results in an estimated 1.8 t CO₂‑eq /t of steel. By contrast, steel made using H2-DRI-EAF and low-carbon electricity would generate an estimated 0.12 t CO₂‑eq /t of steel and is a more energy-efficient process. EAF furnaces are already very common in steelmaking and for recycling existing steel, but are rarely combined with H2-DRI. Although H2-DRI was first used on an industrial scale in 2001, that plant was shut down for economic and political reasons, and economics remain a barrier. Finally, technologies to make industrial hydrogen from electricity are mature, but most hydrogen produced today is made from fossil fuels and is carbon-intensive. Active research is exploring other technologies that could become important for improving steel production in the future, most notably aqueous or molten oxide electrolysis, both of which use electricity to directly remove oxygen from iron ore, and can be combined with EAF to make steel.
Steelmaking is classified as a hard-to-abate industry, and H2-DRI-EAF powered by clean electricity is considered one of the best strategies for cutting emissions in this sector. The Net Zero Industry project forecasts that under an emissions-neutral steel scenario by 2050, roughly 40% of global steel production could depend on H2-DRI-EAF, with the remainder consisting of recycled steel (47%), steelmaking with CCS (11%), or technologies not yet defined (2%). The impact is potentially significant, given that steelmaking accounted for an estimated 3.7 Gt of CO₂‑eq in 2019. Improved steelmaking has the additional benefit of reducing air and land pollution, as burning coal releases fine particulate matter, heavy metals, and other pollutants. In China, steel production is the largest industrial source of air pollution. As demand for steel is expected to increase up to 30% by 2050 due to demand from India and other low- and middle-income countries, it is critical that new and existing production shift to cleaner, lower-emission technologies, and that policies supporting this shift be implemented.
While proposed low-emission steel projects have attracted significant attention from the press, many have since been canceled or put on hold. As of 2025, we could find references to only a few pilot facilities producing improved steel as we have defined it here. The entire H2-DRI-EAF process is considered to be at the large-scale prototype demonstration stage. However, contributing technologies such as electrolytic hydrogen production and EAF are more mature, and H2-DRI was first used on an industrial scale in 2001. The higher cost of making low-emission steel is a significant barrier to industrial adoption and consumer demand. Electricity accounts for nearly half the cost of producing low-emission steel from iron ore. To increase adoption, improved steel facilities need to be located in areas that can readily supply both iron ore and abundant low-carbon, low-cost electricity. In areas such as China, where the electricity grid still relies heavily on fossil fuels, transitioning to H2-DRI-EAF risks increasing emissions unless dedicated renewables are integrated into the project. To move this solution forward, new policies are needed to create an international market for low-emission steel. Meanwhile, existing steelmaking facilities typically have lifetimes of 25–40 years, which increases the likelihood of stranded assets or continued reliance on fossil fuels by 2050. Under its Sustainable Development Scenario, the International Energy Agency (IEA) projects that, by 2050, only 12% of cumulative direct emissions reductions in steelmaking will be due to electrification and the use of hydrogen (the IEA considered emissions from electricity to be indirect). Reducing demand for steel, incremental efficiency gains, and CCS are expected to make up the bulk of cumulative direct emissions reductions, according to the IEA projections.
Bataille, C., Stiebert, S., Li, F. (2021). Global facility level net-zero steel pathways. Net Zero Steel. Link to source: https://netzeroindustry.org/wp-content/uploads/pdf/net_zero_steel_report.pdf
Devlin, A., Kossen, J., Goldie-Jones, H., & Yang, A. (2023). Global green hydrogen-based steel opportunities surrounding high quality renewable energy and iron ore deposits. Nature Communications, 14(1), 2578. Link to source: https://doi.org/10.1038/s41467-023-38123-2
Hubner Australia. (n.d.). Green steel manufacturing: Processes and comparisons. Hubner Australia. Link to source: https://hubner.au/green-steel-manufacturing/
IEA. (2020). Iron and steel technology roadmap. Link to source: https://iea.blob.core.windows.net/assets/eb0c8ec1-3665-4959-97d0-187ceca189a8/Iron_and_Steel_Technology_Roadmap.pdf
Kueppers, M., Hall, W., Levi, P., Simon, R., & Vass, T. (2023, July 11). Steel. IEA. Link to source: https://www.iea.org/energy-system/industry/steel
Lang, S., Kopf, M., & Valery, R. (2021, November 18). Cicored fine ore direct reduction—A proven process to decarbonize steelmaking. Metso. Link to source: https://www.metso.com/insights/blog/mining-and-metals/circored-fine-ore-direct-reduction-a-proven-process-to-decarbonize-steelmaking/
Leadit. (2025, May). Green steel tracker. Leadit Leadership Group for Industry Transition. Link to source: https://www.industrytransition.org/green-steel-tracker/
McKinsey & Company. (2024). Green-steel hubs: A pathway to decarbonize the steel industry. McKinsey & Company. Link to source: https://www.mckinsey.com/industries/metals-and-mining/our-insights/green-steel-hubs-a-pathway-to-decarbonize-the-steel-industry#/
Milne, R. (2025, October 13). Flagship green steel start-up in funding crisis as Europe’s low-carbon ambitions falter. Financial Times. Link to source: https://www.ft.com/content/ac619c2d-9c7a-4208-baa5-6c648d10cacc
Net Zero Industry. (n.d.). Net zero steel pathways. Net Zero Industry. Link to source: https://netzeroindustry.org/net-zero-parhways /
Russell, C. (2025, May 29). Green steel is distant and expensive, but teal steel is coming. Reuters. Link to source: https://www.reuters.com/markets/commodities/green-steel-is-distant-expensive-teal-steel-is-coming-russell-2025-05-29/
Ryan, N. A., Miller, S. A., Skerlos, S. J., & Cooper, D. R. (2020). Reducing CO2 emissions from U.S. steel consumption by 70% by 2050. Environmental Science & Technology, 54(22). Link to source: https://doi.org/10.1021/acs.est.0c04321
Wrede, I. (2025, July 19). ArcelorMittal’s pullout plunges German green steel in doubt. DW. Link to source: https://www.dw.com/en/arcelormittals-pullout-plunges-german-green-steel-in-doubt/a-73303680
Zhang, J., Shen, H., Chen, Y., Meng, J., Li, J., He, J., Guo, P., Dai, R., Zhang, Y., Xu, R., Wang, J., Zheng, S., Lei, T., Shen, G., Wang, C., Ye, J., Zhu, L., Sun, H. Z., Fu, T.-M., … Tao, S. (2023). Iron and Steel Industry Emissions: A Global Analysis of Trends and Drivers. Environmental Science & Technology, 57(43), 16477–16488. Link to source: https://doi.org/10.1021/acs.est.3c05474
Improving district heating for industry involves using low-carbon alternatives, such as electric boilers, heat pumps, and waste heat from other industries, to provide heat to industries for their operations. Currently, most district heating for industry relies heavily on fossil fuels to generate heat. Low-carbon alternatives have the potential to make a significant dent in the global emissions from industry, but such projects are also challenging to implement due to their scale and complexity, and there is currently a lack of publicly available data that would allow for a deeper analysis. Based on our assessment, we will “Keep Watching” this potential solution.
Based on our analysis, improving district heating for industry by integrating low-carbon heat sources has the potential to significantly reduce the use of fossil fuels and the emissions they generate. However, the lack of data, combined with the complexity of such projects and the growing interest in alternative decarbonization pathways, makes this a potential solution to “Keep Watching.”
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | No |
| Effective | Does it consistently work? | Yes |
| Impact | Is it big enough to matter? | Yes |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
District heating systems consist of a network of underground pipes that distribute heat to a large number of buildings, including industrial buildings. In the industrial sector, district heating is used by light industries and for processes such as drying, paper making, food processing, as well as space heating and even heat-driven chillers for refrigeration. Industry is well-suited to district heating because it typically has steady and predictable heat demand throughout the year. Current district heating systems rely heavily on coal and natural gas for heat generation, often as part of combined heat and power generation. Low-carbon alternatives for district heating can include electric heat pumps, solar thermal, deep geothermal, and even waste heat from other industries.
Shifting district heating for industry from conventional heat sources to low-carbon heat sources will significantly reduce emissions. Our analysis for district heating use by commercial and residential buildings shows that significant emissions can be avoided by shifting to electric boilers, heat pumps, and the use of waste heat (see Improve District Heating: Buildings). Similar outcomes are likely possible for industrial district heating use, and emissions reductions will increase as more renewables are integrated into the electricity systems used to power electric boilers and heat pumps.
District heating for industry currently produces significant emissions. According to the International Energy Agency (IEA), district heating for all applications accounted for 4% of global emissions in 2022, and roughly 40% of the heat energy from district heating was delivered to industry. China is a major adopter of district heating for industries, with the combustion of coal supplying much of that heat. The shift to renewable heat sources is likely to increase because both China and the EU have policies targeting the adoption of renewables in district heating. Because district heating systems serve multiple buildings, a single project to replace fossil fuels with renewables can have a large impact. Such projects also have the benefit of reducing local air pollution.
Although simple on paper, replacing fossil fuel systems with lower-carbon alternatives in district heating systems can be an extended undertaking involving many stakeholders and years of planning. Some low-carbon options may not be suitable for industrial processes that require higher temperatures than those needed for space heating. There is also a significant lack of publicly available data about how industry currently uses district heating and the opportunities and challenges involved in shifting to renewables. In the meantime, industrial heat pumps with higher temperature outputs (100–200°C) are increasingly available and could become a low-carbon competitor to the use of a conventional district heating system.
Bellevrat, E., & West, K. (2018). Clean and efficient heat for industry. IEA. Link to source: https://www.iea.org/commentaries/clean-and-efficient-heat-for-industry
Difs, K., Danestig, M., & Trygg, L. (2009). Increased use of district heating in industrial processes – Impacts on heat load duration. Applied Energy, 86(11), 2327–2334. Link to source: https://doi.org/10.1016/j.apenergy.2009.03.011
European Commission. (2022). Implementing the repower EU action plan: Investment needs, hydrogen accelerator and achieving the bio-methane targets. Link to source: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52022SC0230
Gouy, A., Mooney, E., & Voswinkel, F. (2023). Light Industry. IEA. Link to source: https://www.iea.org/energy-system/industry/light-industry
IEA. (2025). District heating. Link to source: https://www.iea.org/energy-system/buildings/district-heating#programmes
IRENA, IEA, & REN21. (2020). Renewable energy policies in a time of transition: Heating and cooling. Link to source: https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2020/Nov/IRENA_IEA_REN21_Policies_Heating_Cooling_2020.pdf
Lake, A., Rezaie, B., & Beyerlein, S. (2017). Review of district heating and cooling systems for a sustainable future. Renewable and Sustainable Energy Reviews, 67, 417–425. Link to source: https://doi.org/10.1016/j.rser.2016.09.061
Werner, S. (2017). International review of district heating and cooling. Energy, 137, 617–631. Link to source: https://doi.org/10.1016/j.energy.2017.04.045
Blue hydrogen production involves making hydrogen (H2) from fossil fuel feedstocks while using carbon capture and storage (CCS) to reduce CO₂ emissions from the production process. The captured CO₂ is concentrated, compressed, and permanently stored underground. Blue hydrogen is more expensive than grey hydrogen, the predominant hydrogen production method, but less expensive than zero-emissions green hydrogen. Blue hydrogen production could facilitate the expansion of hydrogen infrastructure and the development of the global hydrogen economy. However, current adoption is low, its effectiveness at reducing GHG emissions is variable, and it could compete with technologies that offer greater climate benefits. Because of its reliance on fossil fuels for both feedstock and energy, the expansion of blue hydrogen production would perpetuate and potentially expand the use of fossil fuels. Based on this risk, we conclude that producing blue hydrogen is “Not Recommended” as a climate solution.
Based on our analysis, blue hydrogen is feasible and ready to deploy, but there is little real-world evidence for its effectiveness or ability to scale. The expansion of this technology to replace current grey hydrogen production or to support the transition to a global hydrogen economy will perpetuate and possibly expand the use of fossil fuels. Because of this risk, we conclude that producing blue hydrogen is “Not Recommended”.
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Limited |
| Effective | Does it consistently work? | No |
| Impact | Is it big enough to matter? | No |
| Risk | Is it risky or harmful? | Yes |
| Cost | Is it cheap? | Yes |
Blue hydrogen production is an industrial process that produces hydrogen (H2) from fossil fuels – either natural gas or coal – combined with carbon capture and storage (CCS) technology to reduce CO₂ emissions produced during the process. Today, most hydrogen is grey hydrogen made from natural gas without any CCS. The addition of CCS prevents the release of some of the CO₂ generated during the hydrogen production process; capturing, concentrating, and then storing it permanently underground.
The technologies for making hydrogen from natural gas, predominantly steam methane reformation (SMR), are well-established and have been used to produce hydrogen for close to a century. CCS technology is also available and currently deployed in multiple industrial and power generation applications. The SMR hydrogen production process generates GHG emissions from two sources: methane leaks from the gas used as feedstock and fuel used to power the production process, and GHG emissions from both the SMR process and combustion of gas (or other fuels) for energy, including CO₂, methane, nitrous oxide, and black carbon. CCS can be applied to capture CO₂ produced during the SMR process, for post-combustion capture of CO₂ from the plant’s energy use, or for both. Incorporating CCS to capture emissions from the H2 production process adds costs and increases energy use, but it could theoretically reduce CO₂ emissions by more than 90%. However, current adoption of blue hydrogen is very low – less than 1% of global hydrogen production – and there is little real-world evidence to support its effectiveness and scalability. The few commercial facilities currently in operation capture only about 60% or less of the emitted CO₂. Because CCS is energy-intensive, it requires more fuel to power the blue hydrogen production plant. This can also increase fugitive methane leaks due to increased gas-powered energy consumption. If implemented adequately, carbon storage can be permanent. The captured CO₂ can also be used as a chemical precursor for the manufacture of other products or for enhanced oil recovery; however, these post-capture uses of CO₂ emit GHGs, thereby reducing or eliminating the emissions reduction efficacy of CCS. Currently, only ~8% of CO₂ captured from blue hydrogen production is injected into dedicated geological storage, with the rest used in industry, enhanced oil recovery, and other applications.
Hydrogen can be combusted as a zero-emissions fuel, used to store energy to produce electricity, or deployed as a feedstock in industrial, transportation, and energy systems. The production of any hydrogen type – blue, grey, or green hydrogen – could facilitate the expansion of hydrogen infrastructure and the development of the global hydrogen economy, which is an important step in scaling hydrogen. Blue hydrogen is more technologically ready and cheaper than green hydrogen, which is made from water using electrolysis powered by renewable energy. Blue hydrogen is more expensive to produce than grey hydrogen, but the cost per ton of CO₂ removed could be relatively low. Estimates range from US$60–110/t CO₂, although these costs are uncertain and, with lower CCS effectiveness, they could increase to ~US$260/t CO₂. If implemented with low fugitive methane emissions and high CCS efficiencies, blue hydrogen could substantially reduce emissions compared to current grey hydrogen production. The climate impact of scaling blue hydrogen could be high. Estimates and targets for blue hydrogen production by 2050 range from ~30–85 Mt H2. At that scale, even modest emissions savings relative to grey hydrogen would have a climate impact above 0.09 Gt CO₂‑eq/yr by 2050. However, achieving this depends on the quality of the infrastructure and rate of technology scaling, both of which are unproven.
Currently, 6% of the world’s natural gas and 2% of its coal are used to make hydrogen. As hydrogen production ramps up, blue hydrogen – even though it reduces production emissions compared to grey hydrogen – would perpetuate and could even increase the global market for fossil fuels. If the future implementation of green hydrogen is set back, blue hydrogen could create a long-term dependency on fossil fuels. Furthermore, any hydrogen produced from natural gas leads to methane leaks, regardless of whether CO₂ is captured. Methane is a potent short-lived GHG, meaning its impact on climate warming is stronger in the near-term. This is why reducing methane emissions is an urgent emergency brake climate action. Building and expanding a new industry that relies on natural gas as both a feedstock and fuel, and which inevitably leaks methane, is counterproductive to solving the climate crisis.
If and when there is a transition to a global hydrogen economy, blue hydrogen is a less effective climate solution than green hydrogen. Although this technology could be a transitional solution between grey and green hydrogen, blue hydrogen risks diverting resources away from green hydrogen development or ready-to-deploy renewable energy technologies, such as onshore wind or distributed solar PV. There are mixed expert opinions about the realistic level of avoided emissions that blue hydrogen may reach. Additionally, there is uncertainty around whether CCS can meet its technical potential at a reasonable cost.
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Collodi, G., Azzaro, G., Ferrari, N., & Santos, S. (2017). Techno-economic evaluation of deploying CCS in SMR based merchant H2 production with NG as feedstock and fuel. Energy Procedia, 114, 2690–2712. Link to source: https://doi.org/10.1016/j.egypro.2017.03.1533
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Hossain Bhuiyan, M. M., & Siddique, Z. (2025). Hydrogen as an alternative fuel: A comprehensive review of challenges and opportunities in production, storage, and transportation. International Journal of Hydrogen Energy, 102, 1026–1044. https://doi.org/10.1016/j.ijhydene.2025.01.033
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IEA. (2023a). Hydrogen: Net zero emissions guide. Link to source: https://www.iea.org/reports/hydrogen-2156#overview
IEA. (2023b). Net zero roadmap: A global pathway to keep the 1.5 °C goal in reach. Link to source: https://www.iea.org/reports/net-zero-roadmap-a-global-pathway-to-keep-the-15-0c-goal-in-reach
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Bioplastics are renewable, plant-based alternatives to conventional plastics that can reduce emissions by replacing fossil-based feedstocks with biogenic carbon feedstocks. These feedstocks are biomass materials that absorb atmospheric CO₂ during growth and serve as the carbon source for plastic production. The chemical and biological properties of bioplastics are well understood, commercially validated, and can reduce emissions when produced sustainably and managed properly at their end-of-life. Benefits include reducing fossil fuel reliance, alleviating plastic pollution, and, in targeted uses, supporting circularity. However, these are counterbalanced by their inconsistent emissions savings, high costs, and scalability constraints. We conclude that deploying bioplastics as plastic alternatives remains a climate solution to “Keep Watching”, but would require changes in feedstock and appropriate end-of-life infrastructure to achieve reliable emissions reductions.
Based on our analysis, the widespread use of bioplastics is challenged by their potential ecological risks and currently high costs. While bioplastics offer some environmental benefits in niche applications, their climate impact is inconsistent and hinges on feedstock type, manufacturing practices, and waste management. Therefore, we conclude that Deploy Bioplastics is a solution to “Keep Watching.”
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | No |
| Impact | Is it big enough to matter? | No |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
Bioplastics (also called biopolymers) are plastic alternatives made from renewable biological sources, such as corn, sugarcane, crop residues, or other plants, instead of fossil fuels. Bioplastics are produced by extracting sugars or starches from plants and converting them through chemical or biological processes into chemical building blocks that form the basic structure of plastics. Because plants absorb atmospheric CO₂ through photosynthesis, the carbon stored in bioplastics is considered biogenic, as it is already part of the natural carbon cycle. In contrast, petrochemical plastics are made by extracting and refining oil or natural gas, which releases new (formerly buried) carbon into the atmosphere. Bioplastics cut emissions by replacing fossil carbon feedstocks with biomass-based feedstocks. Some bioplastics are durable, non-biodegradable, chemically identical to traditional plastics (i.e., “drop-in” bioplastics), and recyclable. Others are biodegradable and can be designed to break down in compost. Emissions from bioplastics come from growing and processing biomass (which requires energy and land use), manufacturing the plastics, and managing their end-of-life waste. Bioplastics can achieve climate benefits when the emissions from production and end of life are kept low enough to realize the advantages of biogenic carbon.
The basic idea of bioplastics is scientifically and chemically sound, with their development and commercialization ongoing since the 1990s. Numerous studies support the effectiveness of bioplastics in reducing atmospheric CO₂ emissions from feedstock production and manufacturing stages compared to fossil-based plastics, particularly when made from sustainably sourced biomass under energy-efficient conditions and properly composted or recycled. However, other studies show bioplastics have inconsistent emissions reduction performance. Global adoption also remains limited, representing only about 0.5% of total plastics production (approximately 2–2.5 Mt out of 414 Mt, according to European Bioplastics).
Bioplastics, particularly biologically derived and biodegradable polymers, have functional advantages in reducing fossil fuel dependence and mitigating plastic pollution. By sourcing raw materials from renewable biomass instead of petroleum (e.g., oil, natural gas), bioplastics can lower CO₂ emissions in the production stage, especially when accounting for biogenic carbon uptake during plant cultivation. Some types of bioplastics are interchangeable with traditional plastics and can be produced with existing plastic manufacturing systems, easing the transition. Compostable plastics simplify disposal in applications where contamination with food or organic waste occurs, enabling organic recycling and returning carbon and other nutrients to soil. Biodegradable bioplastics are also advantageous for products that are often discarded and may leak into the environment. Studies show that two widely used commercial bioplastics, polylactic acid (PLA) and polyhydroxybutyrate (PHB), biodegrade 60–80% in composting conditions within 28–30 days, while cellulose-based and starch-based plastics can fully degrade in soil and marine environments in 180 days and 50 days, respectively. These functional benefits, combined with potential additional benefits, such as soil enrichment and waste stream simplification, make bioplastics appealing in specific, targeted use cases. More broadly, they can significantly contribute to emissions reduction efforts in materials production when designed for circularity and supported by infrastructure that facilitates appropriate end-of-life waste treatment.
Despite their promise, bioplastics have several limitations as a viable climate solution, including relatively low emissions reduction potential and possible risks and adverse impacts from their large-scale deployment. Current production is low. To reach a meaningful 20–30% marketplace share by 2040, bioplastics would need to expand manufacturing by approximately 30% per year, nearly double the current pace. This could put pressure on land and food systems, since current bioplastics rely on food-based crops for industrial-level production. This raises sustainability concerns around food security and could potentially drive unintended land-use changes such as deforestation or cropland conversion. Furthermore, the effectiveness of reducing emissions by replacing conventional plastics with bioplastics is low and inconsistent. Some bioplastics produce more life cycle emissions than conventional plastics. The likely climate impact of replacing 20–30% of traditional plastics with bioplastics is <0.1 Gt CO₂‑eq/yr. End-of-life treatment is also a major challenge. Many bioplastics are incompatible with home composting and current recycling streams, and improperly composted or landfilled biodegradable bioplastics can emit methane. Finally, bioplastics remain 2–3 times more expensive than conventional plastics.
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Recycling is a mechanical process that repurposes waste into new products without altering their chemical structure. This solution focuses on four common waste types: metals, paper and cardboard, plastics, and glass. It reduces GHG emissions by minimizing reliance on energy-intensive primary material production, reducing demand for raw materials, and diverting paper from landfills, where decomposition can produce methane.
Our focus is on postconsumer municipal solid waste (MSW) collected through residential and commercial recycling programs. Textiles, rubber, wood, and e-waste are also important waste streams but are excluded in our scope due to limited availability of global data. Organic waste is addressed separately in other Drawdown Explorer solutions, including Increase Centralized Composting, Increase Decentralized Composting, and Produce Biochar.
Mechanical recycling mitigates GHG emissions by reducing the need for more energy-intensive and pollutant-emitting raw material extraction and processing (Stegmann et al., 2022; Sun et al., 2018; Zier et al., 2021) and reducing production of methane from decomposing paper in landfills (Demetrious & Crossin, 2019; Lee et al., 2017).
Recyclable materials constitute a significant portion of global MSW, with average compositions of approximately 14% paper and cardboard, 10% plastics, 4% glass, and 3.5% metals (Kaza et al., 2018; United Nations Environment Programme [UNEP], 2024). Recycling reprocesses postconsumer materials into secondary raw materials or products without altering their chemical composition..
Figure 1 illustrates a typical single-stream recycling system at a materials recovery facility (MRF), where mechanical and optical sorting technologies separate materials by type (Gundupalli et al., 2017; Zhang et al., 2022). The sorted materials then undergo cleaning, crushing or shredding, and remelting or repulping in preparation for use in manufacturing new products.
Metals recycling provides ferrous and nonferrous inputs for the metal production sector, which globally emits an estimated 3.6 Gt CO₂‑eq/yr for 2–3 Gt of primary metal output (Azadi et al., 2020). Virgin (primary) metals are extracted from nonrenewable ores; as higher-grade ores are consumed, mining shifts to lower-grade ore deposits, which require more energy-intensive extraction and processing (Norgate & Jahanshahi, 2011). Using recycled metals in place of virgin metals reduces energy requirements for smelting and refining (Daehn et al., 2022) and water use during production.
Virgin ore processing primarily emits CO₂, with smaller contributions of methane and nitrous oxide. Some primary metal production, particularly aluminum production, emits fluorinated gases (F-gases) (Raabe et al., 2019; Raabe et al., 2022). Recycling emits significantly less CO₂ than primary production.
Paper and cardboard recycling involves hydropulping, deinking, and reforming recovered fibers into new paper products. Conventional paper is produced from virgin tree pulp and involves harvesting, debarking, chipping, and mechanical or chemical pulping. Pulp-making alone accounts for 62% of energy use and 45% of emissions in paper production (Sun et al., 2018), contributing significantly to the 1.3–2% of global GHG emissions from virgin pulp and paper manufacturing (Furszyfer Del Rio et al., 2022). Recycling uses less energy and produces fewer GHG emissions. Recycling 1 t of paper saves ~17 mature trees (U.S. Environmental Protection Agency [U.S. EPA], 2016a), lessening deforestation from harvesting and reducing the energy and water required for pulping. Recovering used paper from landfills further avoids decomposition-related methane release.
Plastics recycling involves melting plastic waste into resin, forming it into granules or pellets, and using it to manufacture new products. The primary production of plastics represents 4.5–5.3% of total global GHG emissions (Cabernard et al., 2022; Karali et al., 2024), with ~75% occurring in the early life-cycle stages. More than 99% of plastics are derived from fossil fuels. Recycling plastics reduces CO₂ and methane emissions by replacing petroleum-based feedstock with recycled plastic.
Glass recycling crushes glass waste into cullet, which can then be melted and reintroduced as a raw material in glass manufacturing. Virgin glass production requires melting raw materials such as silica sand, soda ash, and limestone at ~1,500 °C (Baek et al., 2025; Westbroek et al., 2021) and releases CO₂ from decomposition of carbonates. Cullet use releases no CO₂ from carbonate decomposition and lowers the melting temperature, reducing furnace fuel combustion.
This assessment evaluates metal, paper and cardboard, plastic, and glass recycling separately to better capture the distinct emissions profiles and cost requirements of each material, providing a clearer understanding of the climate benefits and trade-offs.
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Nina-Francesca Farac, Ph.D.
Ruthie Burrows, Ph.D.
James Gerber, Ph.D.
Daniel Jasper
Alex Sweeney
Emily Cassidy
Megan Matthews, Ph.D.
Christina Swanson, Ph.D.
We estimated recycling effectiveness as the net emissions savings from avoided primary manufacturing and landfilling, minus the emissions associated with recycling, as outlined in Equation 1 (see Caveats for more information on technical substitutability ratios [TSRs]). We included landfilling emissions only for materials that generate meaningful end-of-life GHG impacts. Paper and cardboard emit both biogenic CO₂ and methane emissions from anaerobic decomposition (Lee et al., 2017), and plastics contribute minor emissions from landfill handling due to their inert nature (Chamas et al., 2020; Zheng & Suh, 2019). Metals and glass are also considered inert and do not biodegrade. Their landfilling emissions are primarily from collection and transport, which fall outside the scope of this analysis.
Equation 1.
Metals recycling has a high carbon abatement potential of 1,480,000 t CO₂‑eq /Mt metal waste recycled (1,650,000 t CO₂‑eq /Mt metal waste recycled, 20-year basis) (Table 1a). In our analysis, metal recycling emissions were about one-third of those from primary metal production.
Paper and cardboard recycling has a similar carbon abatement potential of 1,000,000 t CO₂‑eq /Mt paper and cardboard waste recycled (1,000,000 t CO₂‑eq /Mt paper and cardboard waste recycled, 20-year basis) (Table 1b). Although recycling lowers fossil fuel use in pulping, our estimates showed only slightly lower emissions than primary manufacturing. In contrast, preventing CO₂ and methane release from decomposing paper in landfills have comparable emissions to primary production, making landfill diversion the larger climate impact.
Plastics recycling is the most effective of the four materials at reducing emissions, eliminating approximately 2,000,000 t CO₂‑eq /Mt plastic waste recycled (3,000,000 t CO₂‑eq /Mt plastic waste recycled, 20-year basis) (Table 1c). This is largely due to the high emissions intensity of virgin plastic production, which reached global production volumes of 374 Mt in 2023 (Plastics Europe, 2024a) and relies heavily on fossil fuels both as feedstocks and as energy sources for heat generation. While pellet-to-product conversion contributes to overall emissions, plastic pellet manufacturing accounts for most GHGs emitted in the plastic supply chain (Zhu et al., 2025). For studies without clearly defined boundaries, we assumed the reported emissions primarily reflected pellet production.
Glass recycling is the least effective at reducing emissions but still abates a meaningful amount at 79,000 t CO₂‑eq /Mt glass waste recycled (84,000 t CO₂‑eq /Mt glass waste recycled) (Table 1d). Emissions savings come from reduced fuel use in high-temperature melting furnaces and avoiding CO₂ release during the processing of raw materials (Baek et al., 2025).
While nitrous oxide is also released from fuel combustion during recycling of metals, paper and cardboard, plastics, and glass, it represents a small share of total CO₂‑eq emissions, so we considered it negligible (U.S. EPA, 2016b; Diaz & Warith, 2006).
Table 1. Effectiveness at reducing emissions.
Unit: t CO₂‑eq /Mt metal waste recycled, 100-yr basis
| 25th percentile | 1,410,000 |
| Mean | 1,480,000 |
| Median (50th percentile) | 1,480,000 |
| 75th percentile | 1,550,000 |
Unit: t CO₂‑eq /Mt paper and cardboard waste recycled, 100-yr basis
| 25th percentile | 600,000 |
| Mean | 1,000,000 |
| Median (50th percentile) | 1,000,000 |
| 75th percentile | 2,000,000 |
Unit: t CO₂‑eq /Mt plastic waste recycled, 100-yr basis
| 25th percentile | 2,000,000 |
| Mean | 2,000,000 |
| Median (50th percentile) | 2,000,000 |
| 75th percentile | 2,000,000 |
Unit: t CO₂‑eq /Mt glass waste recycled, 100-yr basis
| 25th percentile | 58,000 |
| Mean | 79,000 |
| Median (50th percentile) | 79,000 |
| 75th percentile | 100,000 |
Emissions mitigation from recycling metals and paper and cardboard results in net cost savings, while plastics break even and glass remains cost-intensive. Initial capital costs for all four material recycling systems are higher than for landfilling, but operating costs are lower. Net landfilling costs are overall profitable for all four materials (see Increase Centralized Composting and Improve Landfill Management for more information on landfilling costs). While operational costs for recycling can vary based on the design and efficiency of MRFs, overall savings can result from reduced landfill tipping fees, lower disposal volume, and revenue from selling recovered materials. These economic factors are determined by energy savings, market demand, and materials-specific recovery efficiencies.
Metals recycling generates net net savings of US$200 million/Mt metal waste recycled, or US$100/t CO₂‑eq mitigated (Table 2a). In addition to significantly reduced energy use and raw material costs (DebRoy & Elmer, 2024), metals recycling delivers high-quality materials comparable to newly mined metals (Damgaard et al., 2009). This drives strong market demand, with revenues often covering – and in some cases exceeding – the costs of separation and/or reprocessing alone.
Paper and cardboard recycling has the highest net savings of the four recycling streams compared to landfilling, with US$400 million/Mt paper and cardboard waste recycled. Combining effectiveness with the net costs presented here, we estimated a savings per unit climate impact of US$400/t CO₂‑eq (Table 2b). This reflects the energy and resource efficiency of paper recycling, along with revenue generation from recovered paper sales (Bajpai, 2014).
Plastics recycling costs US$8 million/Mt less than landfilling, yielding a cost saving of US$4/t CO₂‑eq (Table 2c). However, plastics recycling shows the most variability, ranging from modest savings to higher costs than primary material production. Inexpensive virgin plastics, high contamination risk, complex sorting and reprocessing, and weak or volatile market value (Li et al., 2022) make recycling plastics economically challenging without supportive policies or subsidies.
Glass recycling has a net cost of US$700 million/Mt glass waste recycled and the highest cost per unit of climate impact (US$9,000/t CO₂‑eq , Table 2d). This is due to high processing costs, low market value for cullet (e.g., selling for a fraction of the recycling cost; Figure A1), and contamination that limits resale or reuse (Bogner et al., 2007; Ng & Phan, 2021; Olafasakin et al., 2023). Although glass recycling is costly, the societal and environmental benefits are far higher than those of landfilling (Colangelo, 2024).
Financial data were geographically limited. We based cost estimates on global reports with selected studies from India, Saudi Arabia, the United Kingdom, and the United States for landfilling and Canada, the European Union, Germany, Philippines, and the United States for recycling. Transportation and collection of recyclables can add notable costs to waste management, but we did not include them in this analysis. We calculated amortized net cost for landfilling and recycling by subtracting revenues from operating costs and amortized initial costs over a 30-year facility lifetime. Furthermore, revenues reflect market-based prices, which are subject to change based primarily on demand for recyclables.
Table 2. Cost per unit of climate impact.
Unit: 2023 US$/t CO₂‑eq , 100-yr basis
| Median | -100 |
Unit: 2023 US$/t CO₂‑eq , 100-yr basis
| Median | -400 |
Unit: 2023 US$/t CO₂‑eq , 100-yr basis
| Median | -4 |
Unit: 2023 US$/t CO₂‑eq , 100-yr basis
| Median | 9,000 |
We did not consider a learning curve for the Increase Recycling solution due to a lack of global data quantifying cost reductions specific to mechanical recycling technologies. Recycling systems use well-established processes that are already mature and widely deployed.
Recycling costs depend largely on regional factors, including material availability, market prices, infrastructure, and transportation distances. Consumer sorting habits and contamination rates also influence recycling performance and often outweigh potential learning-based cost decreases from technological improvements. Additionally, many mechanical recycling facilities operate near or at peak process efficiency, leaving little room for the technological upgrades that typically lower costs over time.
Speed of action refers to how quickly a climate solution physically affects the atmosphere after it is deployed. This is different from speed of deployment, which is the pace at which solutions are adopted.
At Project Drawdown, we define the speed of action for each climate solution as emergency brake, gradual, or delayed.
Increase Recycling is a GRADUAL climate solution. It has a steady, linear impact on the atmosphere.
Manufacturing emissions reductions due to recycling of metals, paper and cardboard, plastics, and glass are generally both permanent and additional, depending on local regulations and recycling practices. While recycling reduces the need for virgin production of raw materials and associated emissions, several caveats affect the extent of its climate benefits.
There is a low risk that the avoided emissions from increased recycling will be reversed in the next 100 years. Using recycled materials in place of newly extracted (virgin) resources avoids emissions from extraction, refining, and manufacturing. These reductions are considered permanent because the avoided activities occur to a lesser extent and fewer associated emissions are released. Recycling uses less energy and therefore reduces burning of fossil fuels and emits less GHG. Avoided methane emissions from landfilled paper waste also has high permanence.
Emissions reductions from increasing recycling are additional when improvements go beyond what would happen anyway under existing law or infrastructure. Increases in recycled rates, expansion to underdeveloped areas, and improvements in recycled material quality can result in additional climate benefits (Awino & Apitz, 2024; Halog & Anieke, 2021; Oo et al., 2024; Valenzuela-Levi et al., 2021). Efforts to enable or expand closed-loop recycling are also considered additional, especially for glass bottle recycling and in regions without this infrastructure.
Material-specific limitations also apply. Material losses during product use and end-of-life processing limit metals recycling. Many metals are locked in products with long lifespans, difficult-to-separate designs, or technically unrecoverable applications, reducing availability for recycling (Ciacci et al., 2016; Guo et al., 2023). While improved recycling can decrease losses (Charpentier Poncelet et al., 2022), stagnant recycled metal inputs do not match growing metal demand (Watari et al., 2025).
Paper and cardboard can be recycled only five to seven times before fibers degrade beyond usability (Bajpai, 2014; Obradovic and Mishra, 2020), limiting long-term recyclability. Plastic recycling faces similar limits because many plastics degrade after a few cycles and mechanical processes are highly sensitive to contamination (Klotz et al., 2022; Klotz et al., 2023). For glass, downcycling is common due to quality control issues and variable regional demand for high-purity cullet. Van Ewijk et al. (2021) also emphasized that the benefits of paper recycling depend substantially on the carbon intensity of the energy used, highlighting the need to power recycling with low-carbon electricity.
Worldwide, we estimated that metals are recycled at a rate of 740 Mt/yr (Table 3a). We based this on a study by Gorman et al. (2022), which reported that approximately 1,277 Mt of metals were produced globally in 2018 using recycled feedstocks. This value included all types of scrap metals: postconsumer, pre-consumer, and home scrap reused within factories. To isolate postconsumer recycling, we applied a 58% share based on data from the U.S. Geological Survey (USGS, 2022), which gives a typical breakdown of scrap types across major metals. While this ratio is U.S.-based, we used it as a global proxy due to limited international data. Our current adoption estimate accounts for processing losses, contamination, and quality limits that prevent a full 1:1 replacement of virgin metals (Gorman et al., 2022).
We estimated current paper and cardboard recycling at 160 Mt/yr, the median among two global datasets and one report (United Nations Office on Drugs and Crime [UNODC], 2023; Table 3b). The most recent global data were compiled in 2023 by the Food and Agriculture Organization of the United Nations ([FAO], n.d.), and an earlier dataset from a World Bank analysis from 174 countries in 2018 (World Bank, 2018). To estimate postconsumer recycled paper, we assumed a 75% share of total paper waste based on industry averages (European Paper Recycling Council, 2024)..
Plastics are currently recycled at a rate of 35.9 Mt/yr, based on one global dataset (173 countries; World Bank, 2018), two reports, and one study (Table 3c). Plastics Europe (2024a, 2024b) provides data on global mechanically recycled (postconsumer) plastics production, derived from estimations and statistical projections. We assumed the share of postconsumer plastics from Houssini et al. (2025) and World Bank (2018) to be 100% because the vast majority of plastic waste appears to originate from postconsumer sources.
Glass has the lowest current recycling rate at 27 Mt/yr, calculated as the midpoint among one global dataset (168 countries; World Bank, 2018), two reviews (Delbari & Hof, 2024; Ferdous et al., 2021), and one report (Maximize Market Research Private Limited, 2025) (Table 3d). For values based on total waste generation, we used a global production-based recycling rate, which may underestimate actual glass waste recycling due to limited data on postconsumer glass waste.
Since the World Bank (2018) provided data on waste generation in metric tons per year, we applied global recycling rates of 59.3%, 9%, and 21% to the total waste generated for paper and cardboard, plastics, and glass, respectively (see Appendix for details).
Table 3. Current adoption level.
Unit: Mt/yr, 2018
| Estimate (Gorman et al., 2022) | 740 |
Unit: Mt/yr, 2023
| 25th percentile | 150 |
| Mean | 160 |
| Median (50th percentile) | 160 |
| 75th percentile | 180 |
Unit: Mt/yr, 2023
| 25th percentile | 31.2 |
| Mean | 32.0 |
| Median (50th percentile) | 35.9 |
| 75th percentile | 36.6 |
Unit: Mt/yr, 2020
| 25th percentile | 24 |
| Mean | 24 |
| Median (50th percentile) | 27 |
| 75th percentile | 27 |
Postconsumer metals recycling has grown steadily in recent years (Table 4a, Figure 2). We used global data on secondary metals production from Gorman et al. (2022), a 39.1% share of recycled metals from the total addressable market (Gorman et al., 2022), and a 58% postconsumer scrap factor (U.S. Geological Survey, 2022) to estimate the metals recycling adoption trend from 2014 to 2018. Annual adoption varies across this period. Taking the median annual change, we estimate a global adoption trend of 12 Mt/yr/yr, or 1.6% growth year-over-year (YoY). The mean annual change is estimated as 11 Mt/yr/yr, indicating consistent growth in the recovery of metals from end-of-life products.
Paper and cardboard recycling has gradually but inconsistently grown over the past two decades (Table 4b, Figure 2). Using worldwide recovered paper production data from the FAO (n.d.), we estimated the annual change in paper and cardboard waste recycled from 2003 to 2023. We applied a 75% factor to restrict this to postconsumer collection. While early years (2003–2016) in the data generally showed positive adoption, albeit with some fluctuations, more recent years (2017–2023) reflect declines, including noticeable drops in 2021–2022 (–1.9 Mt/yr/yr) and 2022–2023 (–5.4 Mt/yr/yr). The overall adoption trend is mixed despite a brief spike in 2020–2021. Taking the median annual change over the full 20-year period, we estimated a global trend of 2.2 Mt/yr/yr or a 1.3% YoY growth. The mean annual change is slightly higher at 2.8 Mt/yr/yr (2.0% YoY growth), indicating moderate but uneven progress in the recovery of paper and cardboard.
Plastics recycling is slowly increasing as a share of global plastic waste management, but the overall trend remains modest (Table 4c, Figure 2). We used data from the Organisation for Economic Co‑operation and Development ([OECD], 2022a) to estimate global adoption trends from 2000–2019 and supplemented this with 2019–2023 estimates from Plastics Europe (2022, 2023, 2024a). The adoption trend fluctuates from year to year, reflecting variability in collection rates, contamination levels, and recycling infrastructure. Taking the median annual change in recycled plastic waste across 23 years, we estimated a global adoption trend of 1.3 Mt/yr/yr, or 8.5% YoY growth. The mean annual change is slightly higher at 1.4 Mt/yr/yr, suggesting a slow growth in recycling capacity compared with plastic production volumes. However, this progress is uneven across geographies, with some countries expanding recycling systems while others face barriers, including limited infrastructure and low incentives for recovery.
Glass recycling showed a median annual change of 0 Mt/yr/yr and a mean of 0.8 Mt/yr/yr (3.7% growth YoY) from 2009–2019 (Table 4d, Figure 2). These estimates are based on Chen et al. (2020), who modeled World Bank data (Kaza et al., 2018) to generate a global dataset of waste treatment quantities across 217 countries. The apparent absence of change likely reflects limited availability of global data and inconsistent reporting rather than truly flat adoption. Although the dataset from Chen et al. (2020) is comprehensive, it is modeled rather than based on reported figures.
Table 4. Adoption trend.
Unit: Mt/yr/yr, 2014–2018
| 25th percentile | 2.3 |
| Mean | 11 |
| Median (50th percentile) | 12 |
| 75th percentile | 20 |
Unit: Mt/yr/yr, 2003-2023
| 25th percentile | 0.15 |
| Mean | 2.8 |
| Median (50th percentile) | 2.2 |
| 75th percentile | 5.9 |
Unit: Mt/yr/yr, 2000-2023
| 25th percentile | 0.93 |
| Mean | 1.4 |
| Median (50th percentile) | 1.3 |
| 75th percentile | 1.8 |
Unit: Mt/yr/yr, 2009-2019
| 25th percentile | 0 |
| Mean | 0.8 |
| Median (50th percentile) | 0 |
| 75th percentile | 0 |
Figure 2. Trends in recycling adoption of metals (2014–2018), paper & cardboard (2003–2023), plastics (2000–2023), and glass (2009–2019). Adapted from Chen et al. (2020), Gorman et al. (2022), FAO (n.d.), OECD (2022a), and Plastics Europe (2022, 2023, 2024a).
Sources: Chen, D. M.-C., Bodirsky, B. L., Krueger, T., Mishra, A., & Popp, A. (2020). The world’s growing municipal solid waste: Trends and impacts. Environmental Research Letters, 15(7), Article 074021; Food and Agriculture Organization of the United Nations. (n.d.). FAO‑FAOSTAT: Forestry production and trade [Data set]. Retrieved April 25, 2025; Gorman, M. R., Dzombak, D. A., & Frischmann, C. (2022). Potential global GHG emissions reduction from increased adoption of metals recycling. Resources, Conservation and Recycling, 184, Article 106424; Organisation for Economic Co‑operation and Development. (2022a). Global plastics outlook database [Data set]; Plastics Europe. (2022). Plastics – the facts 2022 [Report]; Plastics Europe. (2023). Plastics – the fast facts 2023 [Infographic]; Plastics Europe. (2024a). Plastics – the fast facts 2024 [Infographic].
Metals recycling adoption is expected to remain high, with the global ceiling estimated at 2,100 Mt/yr (Table 5a). This corresponds to 68.2% of total projected metals production by 2050, based on the “maximum scenario” in Gorman et al. (2022). The scenario reflects a best-case technical potential of recycled metals adoption under full utilization of scrap feedstocks (Gorman et al., 2022). It assumes that all available postconsumer, pre-consumer, and home scrap can be recovered and can fully replace as much virgin material as possible using current technologies. We isolated the postconsumer portion as a 58% share of available metal scrap, as outlined in USGS (2022) data.
There is also a strong potential for increased paper and cardboard recycling, with an estimated adoption ceiling of 360 Mt/yr (Table 5b). We assumed a recovery rate of 85% of total global paper production, accounting for practical limits imposed by fiber degradation, contamination, and processing inefficiencies. According to UNODC (2023), about 48% of paper globally is produced from recycled materials, leaving considerable room for improvement. The 85% ceiling also assumes that not all types of paper can be recovered (e.g., sanitary paper or heavily coated grades). Because this value is based on production rather than discarded paper waste, it may slightly underestimate the ceiling based on postconsumer waste generation.
We estimated the adoption ceiling for plastics recycling at 180 Mt/yr (Table 5c). Technical barriers such as contamination, material heterogeneity, and plastic degradation constrain large-scale adoption. We therefore assumed and applied a 70% recycling rate to postconsumer plastic waste streams. We obtained similar estimates across multiple sources reporting global plastic waste generation (Houssini et al., 2025; OECD, 2022b; Stegmann et al., 2022).
We estimated a ceiling of 100 Mt/yr for glass recycling (Table 5d) based on a 90% recovery rate from global waste generation estimates (Chen et al., 2020; Ferdous et al., 2021). Although glass is considered infinitely recyclable, losses due to contamination, sorting inefficiencies, and market constraints limit complete recovery. We included modeled estimates from Chen et al. (2020) to provide a more comprehensive global ceiling due to the scarcity of global data on glass recycling.
For metals and paper and cardboard, values are derived from single datasets; for plastics, rounding across multiple datasets produced identical values across percentiles. Therefore, only the median is shown for these three subsolutions.
Table 5. Adoption ceiling.
Unit: Mt/y
| Estimate (Gorman et al., 2022) | 2,100 |
Unit: Mt/y
| Estimate (UNODC, 2023) | 360 |
Unit: Mt/y
| Median (50th percentile) | 180 |
Unit: Mt/y
| 25th percentile | 94 |
| Mean | 100 |
| Median (50th percentile) | 100 |
| 75th percentile | 110 |
For sources reporting global recycling rates or tonnage for all materials except metals, we define low and high achievable adoption as 25% or 50% increase in the most recently available material-specific recycle rate, respectively.
For metals recycling, achievable adoption is largely shaped by the dynamics of secondary metal production in global commodity markets, which in turn depends on the relative quantity of scrap available (Ciacci et al., 2016). We set achievable adoption at 1,300–1,400 Mt/yr by 2050 (Table 6a), based on the “plausible” and “ambitious” scenarios from Gorman et al. (2022), respectively. These estimates represent 41–48% of projected global metals production and incorporate both postconsumer and pre-consumer scrap, with the postconsumer share standardized at 58% across scenarios (USGS, 2022). Major commodity metals included in these estimates are steel, aluminum, copper, zinc, lead, iron, nickel, and manganese, which together represent more than 99% of all metal demand by mass from 2014–2018 (USGS, 2021). Material availability and infrastructure for downstream scrap processing remain key hurdles (Allwood et al. 2025), although industrial-scale recovery systems are already well established in many high-income countries (Campbell et al., 2022; de Sa & Korinek, 2021).
We estimated the achievable adoption range for paper and cardboard recycling at 220–260 Mt/yr (Table 6b), with an assumed postconsumer share of 75% applied to the total global recycling volumes reported by FAO (n.d.) and UNODC (2023). This range reflects expanded municipal collection, improvements in fiber separation technologies, and increased demand for recovered pulp in paper manufacturing.
Plastics recycling has substantial opportunity for growth, given <10% global recycling rates and the exponential growth of plastic accumulation in the environment (Dokl et al., 2024; Nayanathara Thathsarani Pilapitiya & Ratnayake, 2024). A 25–50% increase in global mechanically recycled plastic volumes would bring the achievable range to 45–54 Mt/yr (Table 6c). While meaningful, these levels are 8–9 times smaller than the 414 Mt of plastic produced in 2023 (Plastics Europe, 2024a). Constraints include the complexity of sorting mixed plastic streams, limited market demand for lower-grade recycled pellets, and insufficient investment in complementary technologies such as chemical recycling, which remains below 0.5 Mt/yr.
For glass recycling, we set an achievable adoption range of 36–48 Mt/yr by 2050, based on harmonized waste modeling and forward-looking estimates from Chen et al. (2020) and Delbari and Hof (2024). However, this scale-up depends substantially on reducing contamination at the collection stage, expanding color- and ceramic-sorting technologies, and improving closed-loop markets for container glass (Baek et al., 2025; Yuan et al., 2024).
Table 6. Range of achievable adoption.
Unit: Mt/yr
| Current adoption | 740 |
| Achievable – low | 1300 |
| Achievable – high | 1400 |
| Adoption ceiling | 2100 |
Unit: Mt/yr
| Current adoption | 160 |
| Achievable – low | 220 |
| Achievable – high | 260 |
| Adoption ceiling | 360 |
Unit: Mt/yr
| Current adoption | 36 |
| Achievable – low | 45 |
| Achievable – high | 54 |
| Adoption ceiling | 180 |
Unit: Mt/yr
| Current adoption | 27 |
| Achievable – low | 36 |
| Achievable – high | 48 |
| Adoption ceiling | 100 |
Increased recycling has strong potential for climate impact, especially in reducing emissions from virgin material production and landfilling waste (see Appendix for waste sector emissions).
Metals recycling has the highest current and achievable GHG emissions savings of the four material categories (Table 7a). At a >500 Mt/yr current adoption rate, we estimate current metals recycling avoids 1.1 Gt CO₂‑eq/yr (1.2 Gt CO₂‑eq/yr, 20-year basis). Our low and high achievable adoption levels reduce 1.9 and 2.1 Gt CO₂‑eq/yr (2.1 and 2.4 Gt CO₂‑eq/yr, 20-year basis), respectively, with annual GHG reductions up to 3.1 Gt CO₂‑eq/yr (3.5 Gt CO₂‑eq/yr, 20-year basis) using the adoption ceiling.
Paper and cardboard recycling currently avoids 0.16 Gt CO₂‑eq/yr (0.16 Gt CO₂‑eq/yr, 20-year basis) (Table 7b). Achievable GHG reduction is 0.22–0.26 Gt CO₂‑eq/yr (0.22–0.26 Gt CO₂‑eq/yr, 20-year basis), with a maximum potential of 0.36 Gt CO₂‑eq/yr (0.36 Gt CO₂‑eq/yr, 20-year basis).
Plastics recycling has a lower current climate impact of 0.07 Gt CO₂‑eq/yr (0.1 Gt CO₂‑eq/yr, 20-year basis), but it has the potential to increase to a ceiling matching that of recycling paper and cardboard (Table 7c). We estimated low and high achievable adoption levels avoid 0.09 and 0.1 Gt CO₂‑eq/yr (0.1 and 0.2 Gt CO₂‑eq/yr, 20-year basis), respectively, with GHG emissions savings of 0.4 Gt CO₂‑eq/yr (0.5 Gt CO₂‑eq/yr, 20-year basis) at the adoption ceiling. The 20-year impacts highlight the mitigated methane emissions associated with oil refining for virgin plastic production, with recycling plastics reducing both the need for petrochemical feedstocks and the volume of waste sent to landfills.
Glass recycling has the lowest current and achievable emissions reductions, avoiding 0.0021 Gt CO₂‑eq/yr (0.0023 Gt CO₂‑eq/yr, 20-year basis) with the potential to increase to 0.0028–0.0038 Gt CO₂‑eq/yr (0.0030–0.0041 Gt CO₂‑eq/yr, 20-year basis) under higher adoption (Table 7d). We estimated a maximum impact ceiling of 0.0079 Gt CO₂‑eq/yr (0.0084 Gt CO₂‑eq/yr, 20-year basis). Although emissions savings are relatively small, glass recycling is still worthwhile to benefit from cullet-driven energy reductions, conserve raw materials, and contribute to larger reductions when combined with other materials in municipal recycling programs.
Table 7. Climate impact at different levels of adoption.
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | 1.1 |
| Achievable – low | 1.9 |
| Achievable – high | 2.1 |
| Adoption ceiling | 3.1 |
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | 0.16 |
| Achievable – low | 0.22 |
| Achievable – high | 0.26 |
| Adoption ceiling | 0.36 |
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | 0.07 |
| Achievable – low | 0.09 |
| Achievable – high | 0.1 |
| Adoption ceiling | 0.4 |
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | 0.0021 |
| Achievable – low | 0.0028 |
| Achievable – high | 0.0038 |
| Adoption ceiling | 0.0079 |
In our analysis, we adjusted emissions reductions from recycling using a TSR, since recycled materials often do not replace virgin materials on a 1:1 basis due to differences in quality, durability, or performance (Nordahl & Scown, 2024). To ensure we didn’t overestimate emissions savings, we applied an average material-specific ratio that adjusted the avoided emissions from primary material production. Recycled paper and cardboard and glass were assigned a ratio of 0.83; metals, 0.90; and plastics, 0.80 (Figure 3). These unitless ratios were based on technical literature (Barbato et al., 2024; Rigamonti et al., 2020; UNEP, 2024; Zheng & Suh, 2019) and were applied consistently across all emissions units for effectiveness.
Figure 3. Conceptual diagram of a general recycling loop for (a) metals, (b) paper & cardboard, (c) plastics, and (d) glass and how technical substitutability determines the maximum share of recycled content due to quality constraints. Graphics for (b), including the MRF and manufacturing plant for (a), (c), and (d), were modified from International Paper (n.d.). BioRender and Canva were used to make the remaining graphics.
International Paper. (n.d.). Paper’s life cycle: The recycling process [Infographic]. Retrieved June 10, 2025.
Recycling can create jobs and reduce energy costs. The National Institutes of Health (NIH) estimated that incinerating or landfilling 10 kt of waste creates one or six jobs respectively, while recycling the same amount of waste creates 36 jobs (NIH Environmental Management System [NEMS], n.d.). A case study in Florida found that increasing recycling rates can lead to small amounts of job growth, with most new jobs concentrated in the recycling processing sector (Liu et al., 2020).
Using recycled materials can reduce the need for imports and support domestic manufacturing (Das et al., 2010; Dussaux & Glachant, 2019). The sale of products manufactured from recyclables instead of virgin materials can translate to economic benefits. A study of recycling systems in Nigeria found that the sale of recyclables could contribute about US$11.7 million to the country’s economy each year and create about 16,562 new jobs (Ayodele et al., 2018).
Materials in landfills can leach into the surrounding environment (McGinty, 2021). Plastics, along with associated additives such as bisphenol A and phthalates, can degrade into microplastics that enter the surrounding ecosystem and food chain, posing health risks to humans (Bauer et al., 2022; Li et al., 2022; Rajmohan et al., 2019; Zheng & Suh, 2019).
In low- and middle-income countries, informal recycling, which involves networks of individuals who sort through waste and sell or recycle it using informal methods, is a common form of waste management (Yang et al., 2018). Increasing recycling in these contexts could formalize this recycling method and improve some of the social and health equity concerns associated with informal recycling, such as exploitation, safety, child labor, and occupational health exposures, and may improve income-earning capabilities (Aparcana & Salhofer, 2013; Yang et al., 2018). Low- and middle-income countries typically face a disproportionate burden of plastic pollution, which could be improved by increasing recycling capacities globally (World Wildlife Fund [WWF], 2023).
Recycling can benefit land resources and soil quality by reducing materials in landfills and incinerators and by reducing the need to extract virgin materials such as timber and minerals (Dussaux & Glachant, 2019; McGinty, 2021; U.S. EPA, 2025). Rajmohan et al. (2019) estimated that about 22–43% of plastic waste reaches landfills. Plastic waste can degrade into microplastics, leaching into surrounding ecosystems and reducing soil fertility (McGinty, 2021; Rajmohan et al., 2019). The environmental benefits of displacing the need for production using virgin materials through recycling may be more significant than reducing landfilling (Geyer et al., 2016). Recycling, along with the use of wood residues, is projected to reduce the demand for wood and fiber, easing pressures of land resources (FAO, 2009).
Recycling can reduce the amount of water needed to produce new materials. For example, using recycled steel to make steel requires 40% less water than using virgin materials (NEMS, n.d.).
Increasing recycling reduces the amount of waste in landfills and incinerators and can reduce harmful pollution associated with landfilling and incineration (U.S. EPA, 2025). Additionally, recycling reduces the need to mine and process new materials, thereby reducing air pollution emitted during these processes (U.S. EPA, 2025)
Increasing metals recycling, paper and cardboard recycling, and plastics recycling can inadvertently increase environmental and human exposure to hazardous chemicals if not properly managed. Exposure to heavy metal fumes can occur while processing metal waste, and concealed pressurized or reactive items in scrap can cause fires or explosions. Chemical additives such as mineral oils and printing inks often persist throughout the paper life cycle and can migrate into the environment and food packaging, posing health risks such as chronic inflammation, endocrine disruption, and cancer (Pivnenko et al., 2016; Sobhani & Palanisami, 2025). Flame retardants, per- and polyfluoroalkyl substances, and other pollutants can leach from materials during and after plastics recycling. Microplastics accumulate at higher concentrations in recycled plastics and are released during all recycling stages (Monclús et al., 2025; Singh & Walker, 2024). Additionally, recycled papers and plastics contain unintentionally added substances, which carry different additives whose composition is often unknown (Monclús et al., 2025; Sobhani & Palanisami, 2025).
Increased plastics collection for recycling without global coordination can lead to disproportionate plastic pollution if high-income countries export plastic waste to low-income countries with inadequate recycling infrastructure (Singh & Walker, 2024).
When glass recycling is included in single-stream systems, glass shards can damage MRF machinery and contaminate other recyclable materials, decreasing their market value (Deer, 2021). Additionally, the heavy weight and fragility of glass means recycling trucks require multiple trips, consuming more fuel and increasing transportation costs.
Another key risk is that materials collected for recycling may ultimately be landfilled when poor market conditions prevent their recovery.
All of these solutions can reuse clean and high-quality recycled materials as a raw material or feedstock or repurpose them as substitute materials in targeted uses. The embodied emissions from the recovered waste used as production or process inputs will be reduced, enhancing the solutions’ net climate impacts and supporting circularity.
Recycling paper and cardboard waste reduces deforestation required for extracting and processing primary raw materials.
Increased adoption of efficient mechanical recycling systems and equipment can improve the rate and cost of scaling similar highly-efficient, complementary technologies (e.g., chemical recycling).
Diverting certain paper and cardboard types from landfills lowers methane emissions available to be captured and sold for biogas revenue. Paper and cardboard recycling also can reduce the amount of material available for methane digesters.
Mt recycled
CO₂ , CH₄
Mt recycled
CO₂ , CH₄
Mt recycled
CO₂ , CH₄
Mt recycled
CO₂ , CH₄
Ciacci et al. (2016) and van Ewijk and Stegemann (2023) noted that as recycling approaches near-total recovery, energy consumption steeply rises, driven by increased decontamination efforts, sorting challenges, and diminished material quality. However, recycling rates are currently low enough that recycling is less carbon intense than primary material manufacturing.
The eventual quality degradation in secondary materials requires supplementation with virgin resources. However, overall embodied emissions are still lower than they would be for producing all-new materials.
Glass recycling poses a trade-off between convenience and recycling efficiency in single-stream systems. Only 40% of glass is repurposed into new products, and the glass can contaminate other materials. Multi-stream or source-separated systems require more effort but achieve 90%-plus recycling rates (Berardocco et al., 2022; Deer, 2021).
Watari et al. (2025) noted that countries can achieve high local recycling rates and high recycled content by importing scrap metals from elsewhere, but with the trade-off that metal production emissions are offshored rather than reduced. This also introduces dependencies on international scrap flows and global supply chains (Guo et al., 2023), which can similarly occur for paper, cardboard, and plastics.
Recycling reduces solid waste, mitigates GHG emissions from landfilled solid waste, and offers significant savings in electricity and fuel consumption (Cudjoe et al., 2021; Kaza et al., 2018; Uekert et al., 2023). UNEP (2024) estimated that 2.1 Gt of municipal solid waste was generated globally in 2020, and projected that to increase to 3.8 Gt by 2050 if action is not taken. Although postconsumer waste contributes ~5% to total global GHG emissions (Oo et al., 2024), around 30–37% of global waste ends up in landfills with only 19% recovered through recycling and composting processes (Kaza et al., 2018; UNEP, 2024).
Three extensive reviews of industrial decarbonization identify four technologies either ready for near-term deployment or already achieving material impact across global industries: electrification, material efficiency, energy efficiency, and circularity driven by increased reuse and recycling (Daehn et al., 2022; Gailani et al., 2024; Rissman et al., 2020). The last includes recovery of the four waste subcategories considered in this solution, where metals and plastics rank among the top six most-produced human-made materials globally (BioCubes, n.d.).
Incorporating recycled metal scraps into manufacturing consumes 30–95% less energy than producing metals from raw feedstocks, where the primary metal sector emits approximately 10% of global GHG emissions from energy-intensive mining, smelting, and refining (Yokoi et al., 2022). Reprocessing 1 t of plastic waste can save up to 130 GJ of energy (Singh & Walker, 2024), and secondary production of plastics with a ~40% global collection rate could mitigate 160 Mt CO₂ /yr in 2050 (Daehn et al., 2022). Glass recycling offers 2–3% energy savings and a 5% reduction in CO₂ emissions from furnace fuel combustion for every 10% increase in cullet content in the melting batch (Baek et al., 2025; Glass Packaging Institute, n.d.; Miserocchi et al., 2024).
We reiterate that GHG savings from recycling are highly sensitive to assumptions such as material quality, contamination rates, transportation distances, and market conditions. These factors introduce uncertainty because recycling benefits can vary depending on the efficiency of recycling systems in practice and market viability.
The results presented in this document summarize findings from 18 reports, 22 reviews and meta-analyses, 41 original studies, nine perspectives, two books, five web articles, and three datasets reflecting the most recent evidence for more than 200 countries.
Figure A1. The % revenue from recyclables compared to the % mass of each recyclable processed in an MRF. Values pertain to 2021 and extracted from Bradshaw et al. 2025.
In addition to applying global recycling rates of 59.3%, 9%, and 21% to the total waste generated for paper & cardboard, plastics, and glass, respectively (World Bank, 2018; Table A1), we also calculated total tonnage recycled using reported recycling percentages and total MSW tonnage for each country. Combined recycled percentages were consistently lower than the total combined percentage of metal, paper & cardboard, plastic, and glass waste in MSW. This indicates ample opportunity for increased recycling, even in regions where it is already well established.
Table A1. Global recycling rates for each of the waste materials analyzed in this solution.
| Waste material | Global recycling rate (%) | Reference |
|---|---|---|
| Metals | 76a | Charpentier Poncelet et al. (2022) |
| Paper and cardboard | 59.3b | European Paper Recycling Council (2020) |
| Plastics | 9c | OECD (2022b) |
| Glass | 21d |
Ferdous et al. (2021) Westbroek et al. (2021) |
aEstimated using end-of-life recycling rates from Charpentier Poncelet et al. (2022), weighted by average annual global production for aluminum, copper, zinc, lead, iron, nickel, and manganese 2015–2019. We normalized weights against total metal production (1,619 Mt) to reflect each metal’s contribution to global scrap availability. This approach reflects the dominance of aluminum and iron in global scrap flows.
bBased on the average global paper recycling rate in 2018.
cBased on the global plastic recycling rate in 2019.
dBased on total glass produced in 2018 (a production-based recycling rate, meaning the share of recycled cullet used in total glass production), rather than on total glass waste generated (a waste-based recycling rate). We used this value due to a lack of consistent global data on postconsumer (end-of-life, old scrap) glass waste generation, although it may underestimate the recycling rate of actual discarded glass.
The World Bank (2018) also provided country-specific recycling rates and waste composition fractions of MSW for the materials we considered. Metals, paper and cardboard, plastics, and glass were reported as percentages of MSW by 169, 174, 173, and 168 countries, respectively. However, only 125 countries reported recycling rates, and these rates reflect combined MSW rather than material-specific recovery, so the dataset could not be used to estimate achievable adoption ranges for individual materials.
For low achievable adoption, we assumed global recycling increases by 25% of the existing or most recently available rates or total recycled waste tonnage (i.e., recycling volumes) for all four materials except metals. For example, Delbari and Hof (2024) reported 2018 estimates of global glass recycling volumes at 27 Mt annually, so the Adoption – Low recycling rate was calculated at 34 Mt of glass waste recycled/yr.
For high achievable adoption, we assume that global recycling rates increase by 50% of the existing or most recently available rates or total recycled waste tonnage (i.e., recycling volumes) for all four materials except metals. As an example, Houssini et al. (2025) reported global plastic production in 2022, from which 38 Mt were generated as secondary plastics from plastic mechanical recycling. Therefore, the high adoption recycling rate came out to 57 Mt of plastic waste recycled/yr.
According to estimates by Ferdous et al. (2021), Ge et al. (2024), and Oo et al. (2024), the waste sector is responsible for 3.4–5% of total global GHG emissions, with solid waste management of landfills accounting for roughly two-thirds (Ge et al., 2024). In view of this and the energy-intensive production of raw materials, consistently improving recycling efficiency and rates can meaningfully mitigate the world’s carbon output.
Bradshaw, S. L., Aguirre-Villegas, H. A., Boxman, S. E., & Benson, C. H. (2025). Material recovery facilities (MRFs) in the United States: Operations, revenue, and the impact of scale. Waste Management, 193, 317–327. https://doi.org/10.1016/j.wasman.2024.12.008
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A composting system diverts organic waste (OW) from landfills, reducing the production of methane and other GHG emissions. OW is defined as the combination of food waste and green waste, composed of yard and garden trimmings. Composting transforms it into a nutrient-rich soil supplement.
Our focus is on centralized (city- or regional-level) composting systems for the OW components of municipal solid waste (MSW). Decentralized (home- and community-level) and on-farm composting are also valuable climate actions, but are not included here due to limited data availability at the global level (see Increase Decentralized Composting).
There are many stages involved in a composting system to convert organic MSW into finished compost that can be used to improve soil health (Figure 1). Within this system, composting is the biochemical process that transforms OW into a soil amendment rich in nutrients and organic matter.
Figure 1. Stages of a composting system. Solution boundaries exclude activities upstream and downstream of centralized MSW composting such as waste collection and compost application. Modified from Kawai et al. (2020) and Manea et al. (2024).
Sources: Kawai, K., Liu, C., & Gamaralalage, P. J. D. (2020). CCET guideline series on intermediate municipal solid waste treatment technologies: Composting. United Nations Environment Programme; Manea, E. E., Bumbac, C., Dinu, L. R., Bumbac, M., & Nicolescu, C. M. (2024). Composting as a sustainable solution for organic solid waste management: Current practices and potential improvements. Sustainability, 16(15), Article 6329.
The composting process is based on aerobic decomposition, driven by complex interactions among microorganisms, biodegradable materials, and invertebrates and mediated by water and oxygen (see the Appendix). Without the proper balance of oxygen and water, anaerobic decomposition occurs, leading to higher methane emissions during the composting process (Amuah et al., 2022; Manea et al., 2024). Multiple composting methods can be used depending on the amounts and composition of OW feedstocks, land availability, labor availability, finances, policy landscapes, and geography. Some common methods include windrow composting, bay or bin systems, and aerated static piles (Figure 2; Amuah et al., 2022; Ayilara et al., 2020; Cao et al., 2023).
Figure 2. Examples of commonly used centralized composting methods. Bay systems (left) move organics between different bays at different stages of the composting process. Windrows (center) are long, narrow piles that are often turned using large machinery. Aerated static piles (right) can be passively aerated as shown here or actively aerated with specialized blowing equipment.
Credit: Bays, iStock | nikolay100; Windrows, iStock | Jeremy Christensen; Aerated static pile, iStock | AscentXmedia
Centralized composting generally refers to processing large quantities (>90 t/week) of organic MSW (Platt, 2017). Local governments often manage centralized composting as part of an integrated waste management system that can also include recycling non-OW, processing OW anaerobically in methane digesters, landfilling, and incineration (Kaza et al., 2018).
Organic components of MSW include food waste and garden and yard trimmings (Figure 2). In most countries and territories, these make up 40–70% of MSW, with food waste as the largest contribution (Ayilara et al., 2020; Cao et al., 2023; Food and Agriculture Organization [FAO], 2019; Kaza et al., 2018; Manea et al., 2024; U.S. Environmental Protection Agency [U.S. EPA], 2020; U.S. EPA, 2023).
Diverting OW, particularly food waste, from landfill disposal to composting reduces GHG emissions (Ayilara et al., 2020; Cao et al., 2023; FAO, 2019). Diversion of organics from incineration could also have emissions and pollution reduction benefits, but we did not include incineration as a baseline disposal method for comparison since it is predominantly used in high-capacity and higher resourced countries and contributes less than 1% to annual waste-sector emissions (Intergovernmental Panel On Climate Change [IPCC], 2023; Kaza et al., 2018).
Disposal of waste in landfills leads to methane emissions estimated at nearly 1.9 Gt CO₂‑eq (100-yr basis) annually (International Energy Agency [IEA], 2024). Landfill emissions come from anaerobic decomposition of inorganic waste and OW and are primarily methane with smaller contributions from ammonia, nitrous oxide, and CO₂ (Cao et al., 2023; Kawai et al., 2020; Manea et al., 2024). Although CO₂, methane, and nitrous oxide are released during composting, methane emissions are up to two orders of magnitude lower than emissions from landfilling for each metric ton of waste (Ayilara et al., 2020; Cao et al, 2023; FAO, 2019; IEA, 2024; Nordahl et al., 2023; Perez et al., 2023). GHG emissions can be minimized by fine-tuning the nutrient balance during composting.
Depending on the specifics of the composting method used, the full transformation from initial feedstocks to finished compost can take weeks or months (Amuah et al., 2022; Manea et al., 2024; Perez et al., 2023). Finished compost can be sold and used in a variety of ways, including application to agricultural lands and green spaces as well as for soil remediation (Gilbert et al., 2020; Platt et al., 2022; Ricci-Jürgensen et al., 2020a; Sánchez et al., 2025).
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Megan Matthews, Ph. D.
Ruthie Burrows, Ph.D.
James Gerber, Ph.D.
Daniel Jasper
Alex Sweeney
Aiyana Bodi
Hannah Henkin
Ted Otte
Sarah Gleeson, Ph. D.
Amanda D. Smith, Ph.D.
Paul C. West, Ph.D.
We estimated that composting reduces emissions by 3.9 t CO₂‑eq /t OW (9.3 t CO₂‑eq /t OW, 20-yr basis) based on avoided landfill emissions minus the emissions during composting of MSW OW (Table 1). In our analysis, composting emissions were an order of magnitude lower than landfill emissions.
Table 1. Effectiveness at reducing emissions.
Unit: t CO₂‑eq (100-yr basis)/t OW
| 25th percentile | 2.5 |
| Mean | 3.2 |
| Median (50th percentile) | 3.9 |
| 75th percentile | 4.3 |
Emissions data from composting and landfilling OW are geographically limited, but our analysis includes three global reports and studies from the U.S., China, Denmark, and the EU (European Energy Agency [EEA], 2024; Industrious Labs, 2024; Perez et al., 2023; U.S. EPA, 2020; Yang et al., 2017, Yasmin et al., 2022). We assumed OW was 39.6% of MSW in accordance with global averages (Kaza et al., 2018; World Bank, 2018).
We estimated that landfills emit 4.3 t CO₂‑eq /t OW (9.9 t CO₂‑eq /t OW, 20-yr basis). We estimated composting emissions were 10x lower at 0.4 t CO₂‑eq /t OW (0.6 t CO₂‑eq /t OW, 20-yr basis). We quantified emissions from a variety of composting methods and feedstock mixes (Cao et al., 2023; Perez et al., 2023; Yasmin et al., 2022). Consistent with Amuah et al. (2022), we assumed a 60% moisture content by weight to convert reported wet waste quantities to dry waste weights. We based effectiveness estimates only on dry OW weights. For adoption and cost, we did not distinguish between wet and dry OW.
Financial data were geographically limited. We based cost estimates on global reports with selected studies from the U.K., U.S., India, and Saudi Arabia for landfilling and the U.S. and Sri Lanka for composting. Transportation and collection costs can be significant in waste management, but we did not include them in this analysis. We calculated amortized net cost for landfilling and composting by subtracting revenues from operating costs and amortized initial costs over a 30-yr facility lifetime.
Landfill initial costs are one-time investments, while operating expenses, which include maintenance, wages, and labor, vary annually. Environmental costs, including post-closure operations, are not included in our analysis, but some countries impose taxes on landfilling to incentivize alternative disposal methods and offset remediation costs. Landfills generate revenue through tip fees and sales of landfill gas (Environmental Research & Education Foundation [EREF], 2023; Kaza et al., 2018). We estimated that landfilling is profitable, with a net cost of –US$30/t OW.
Initial and operational costs for centralized composting vary depending on method and scale (IPCC, 2023; Manea et al., 2024), but up-front costs are generally cheaper than landfilling. Since composting is labor-intensive and requires monitoring, operating costs can be higher, particularly in regions that do not impose landfilling fees (Manea et al., 2024).
Composting facilities generate revenue through tip fees and sales of compost products. Compost sales alone may not be sufficient to recoup costs, but medium- to large-scale composting facilities are economically viable options for municipalities (Kawai et al., 2020; Manea et al., 2024). We estimated the net composting cost to be US$20/t OW. The positive value indicates that composting is not globally profitable; however, decentralized systems that locally process smaller waste quantities can be profitable using low-cost but highly efficient equipment and methods (see Increase Decentralized Composting).
We estimated that composting costs US$50/t OW more than landfilling. Although composting systems cost more to implement, the societal and environmental costs are greatly reduced compared to landfilling (Yasmin et al., 2022). The high implementation cost is a barrier to adoption in lower-resourced and developing countries (Wilson et al., 2024).
Combining effectiveness with the net costs presented here, we estimated a cost per unit climate impact of US$10/t CO₂‑eq (US$5/t CO₂‑eq , 20-yr basis) (Table 2).
Table 2. Cost per unit climate impact.
Unit: US$ (2023)/t CO₂‑eq (100-yr basis)
| Median | 10 |
Global cost data on composting are limited, and costs can vary depending on composting methods, so we did not quantify a learning rate for centralized composting.
Speed of action refers to how quickly a climate solution physically affects the atmosphere after it is deployed. This is different from speed of deployment, which is the pace at which solutions are adopted.
At Project Drawdown, we define the speed of action for each climate solution as emergency brake, gradual, or delayed.
Increase Centralized Composting is an EMERGENCY BRAKE climate solution. It has the potential to deliver a more rapid impact than nominal and delayed solutions. Because emergency brake solutions can deliver their climate benefits quickly, they can help accelerate our efforts to address dangerous levels of climate change. For this reason, they are a high priority.
The composting process has a low risk of reversal since carbon is stored stably in finished compost instead of decaying and releasing methane in a landfill (Ayilara et al., 2020; Manea et al., 2024). However, a composting system, from collection to finished product, can be challenging to sustain. Along with nitrogen-rich food and green waste, additional carbon-rich biomass, called bulking material, is critical for maintaining optimal composting conditions that minimize GHG emissions. Guaranteeing the availability of sufficient bulking materials can challenge the success of both centralized and decentralized facilities.
Financially and environmentally sustainable composting depends not only on the quality of incoming OW feedstocks, but also on the quality of the final product. Composting businesses require a market for sales of compost products (in green spaces and/or agriculture), and poor source separation could lead to low-quality compost and reduced demand (Kawai et al., 2020; Wilson et al., 2024). Improvements in data collection and quality through good feedback mechanisms can also act as leverage for expanding compost markets, pilot programs, and growing community support.
If composting facilities close due to financial or other barriers, local governments may revert to disposing of organics in landfills. Zoning restrictions also vary broadly across geographies, affecting how easily composting can be implemented (Cao et al., 2023). In regions where centralized composting is just starting, reversal could be more likely without community engagement and local government support (Kawai et al., 2020; Maalouf & Agamuthu, 2023); however, even if facilities close, the emissions savings from past operation cannot be reversed.
We estimated global composting adoption at 78 million t OW/yr, as the median between two datasets (Table 3). The most recent global data on composting were compiled in 2018 from an analysis from 174 countries and territories (World Bank, 2018). We also used an Organisation for Economic Co-operation and Development (OECD) analysis from 45 countries (OECD, 2021). However, there were still many countries and territories that did not report composting data in one or both datasets. Although the World Bank dataset is comprehensive, it is based on data collected in 2011–2018, so more recent, high-quality, global data on composting are needed.
Table 3. Current adoption level (2021).
Unit: t OW composted/yr
| 25th percentile | 67,000,000 |
| Mean | 78,000,000 |
| Median (50th percentile) | 78,000,000 |
| 75th percentile | 89,000,000 |
Globally in 2018, nearly 40% of all waste was disposed of in landfills, 19% was recovered through composting and other recovery and recycling methods, and the remaining waste was either unaccounted for or disposed of through open dumping and wastewater (Kaza et al., 2018)
We calculated total tonnage composted using the reported composting percentages and the total MSW tonnage for each country. Composting percentages were consistently lower than the total percentage of OW present in MSW, suggesting there is ample opportunity for increased composting, even in geographies where it is an established disposal method. In 2018, 26 countries/territories had a composting rate above 10% of MSW, and 15 countries/territories had a composting rate above 20% of MSW. Countries with the highest composting rates were Austria (31%), the Netherlands (27%), and Switzerland (21%) (World Bank, 2018).
We used OECD data to estimate the composting adoption trend from 2014–2021 (OECD, 2021), which fluctuated significantly from year to year (Table 4). Negative rates indicate less OW was composted globally than in the previous year. Taking the median composting rate across seven years, we estimate the global composting trend as 260,000 t OW/yr/yr. However, the mean composting trend is –1.3 Mt OW/yr/yr, suggesting that on average, composting rates are decreasing globally.
Table 4. Adoption trend (2014–2021).
Unit: t OW composted/yr/yr
| 25th percentile | -1,200,000 |
| Mean | -1,300,000 |
| Median (50th percentile) | 260,000 |
| 75th percentile | 4,300,000 |
Although some regions are increasing their composting capacity, others are either not composting or composting less over time. Germany, Italy, Spain, and the EU overall consistently show increases in composting rates year-to-year, while Greece, Japan, Türkiye, and the U.K. show decreasing composting rates. In Europe, the main drivers for consistent adoption were disposal costs, financial penalties, and the landfill directive (Ayilara et al., 2020).
Lack of reported data could also contribute to a negative global average composting rate over the past seven years. A large decline in composting rates from 2018–2019 was driven by a lack of data in 2019 for the U.S. and Canada. If we assumed that the U.S. composted the same tonnage in 2019 as in 2018, instead of no tonnage as reported in the data, then the annual trend for 2018–2019 is much less negative (–450,000 t OW/yr/yr) and the overall mean trend between 2014–2019 would be positive (1,400,000 t OW/yr/yr).
We estimate the global adoption ceiling for Increase Centralized Composting to be 1.35 billion t OW/yr (Table 5). In 2016, 2.01 Gt of MSW were generated, and generation is expected to increase to 3.4 Gt by 2050 (Kaza et al., 2018). Due to limited global data availability on composting infrastructure or policies, we estimated the adoption ceiling based on the projected total MSW for 2050 and assumed the OW fraction remains the same over time.
Table 5. Adoption ceiling. upper limit for adoption level.
Unit: t OW composted/yr
| Median (50th percentile) | 1,350,000,000 |
In reality, amounts of food waste within MSW are also increasing, suggesting that there are sufficient global feedstocks to support widespread composting adoption (Zhu et al., 2023).
We assume that all OW could be processed via composting, but this ceiling is unlikely to be reached. In practice, organics could also be processed via methane digesters (see Deploy Methane Digesters), incinerated, or dumped, but these waste management treatments have similar environmental risks to landfilling.
Since the global annual trend fluctuates, we used country-specific composting rates and organic fractions of MSW from 2018 to estimate the achievable range of composting adoption (see Appendix for an example). In our analysis, achievable increases in country-specific composting rates cannot exceed the total organic fraction of 2018 MSW.
For the 106 countries/territories that did not report composting rates, we defined achievable levels of composting relative to the fraction of OW in MSW. When countries also did not report OW percentages, the country-specific composting rate was kept at zero. For the remaining 86 countries/territories, we assumed that 25% of organic MSW could be diverted to composting for low achievable adoption and that 50% could be diverted for high achievable adoption.
For the 68 countries/territories with reported composting rates, we define low and high achievable adoption as a 25% or 50% increase to the country-specific composting rate, respectively. If the increased rate for either low or high adoption exceeded the country-specific OW fraction of MSW, we assumed that all organic MSW could be composted (see Appendix for an example). Our Achievable – Low adoption level is 201 Mt OW/yr, or 15% of our estimated adoption ceiling (Table 6). Our Achievable – High adoption level is 301 Mt OW/yr, or 22% of our estimated adoption ceiling.
Table 6. Range of achievable adoption levels.
Unit: t OW composted/yr
| Current adoption | 78,000,000 |
| Achievable – low | 201,000,000 |
| Achievable – high | 301,000,000 |
| Adoption ceiling | 1,350,000,000 |
Our estimated adoption levels are conservative because some regions without centralized composting of MSW could have subnational decentralized composting programs that aren’t reflected in global data.
Although our achievable range is conservative compared to the estimated adoption ceiling, increased composting has the potential to reduce GHG emissions from landfills (Table 7). We estimated that current adoption reduces annual GHG emissions by 0.3 Gt CO₂‑eq/yr (0.73 Gt CO₂‑eq/yr, 20-yr basis). Our estimated low and high achievable adoption levels reduce 0.78 and 1.2 Gt CO₂‑eq/yr (1.9 and 2.8 Gt CO₂‑eq/yr, 20-yr basis), respectively. Using the adoption ceiling, we estimate that annual GHG reductions increase to 5.2 Gt CO₂‑eq/yr (12.6 Gt CO₂‑eq/yr, 20-yr basis).
Table 7. Climate impact at different levels of adoption.
Unit: Gt CO₂‑eq (100-yr basis)/yr
| Current adoption | 0.30 |
| Achievable – low | 0.78 |
| Achievable – high | 1.2 |
| Adoption ceiling | 5.2 |
The IPCC estimated in 2023 that the entire waste sector accounted for 3.9% of total global GHG emissions, and solid waste management represented 36% of total waste sector emissions (IPCC, 2023). Disposal of waste in landfills leads to methane emissions estimated at nearly 1.9 Gt CO₂‑eq (100-yr basis) annually (IEA, 2024). Based on these estimates, current composting adoption reduces annual methane emissions from landfills more than 16%.
Increasing adoption to low and high achievable levels could reduce the amount of OW going to landfills by up to 40% and avoid 32–50% of landfill emissions. Reaching our estimated adoption ceilings for Increase Centralized Composting and reduction-focused solutions like Reduce Food Loss and Waste could avoid all food-related landfill emissions.
These climate impacts can be considered underestimates of beneficial mitigation from increased composting since we did not quantify the carbon sequestration benefits of compost application and reduced synthetic fertilizer use. Our estimated climate impacts from composting are also an underestimate because we didn’t include decentralized composting.
Composting creates more jobs than landfills or incinerators and can save money compared with other waste management options (Bekchanov & Mirzabaev, 2018; Farhidi et al., 2022; Platt et al., 2013; Zaman, 2016). It is less expensive to build and maintain composting plants than incinerators (Kawai et al., 2020). According to a survey of Maryland waste sites, composting creates twice as many jobs as landfills and four times as many jobs as incineration plants (Platt et al., 2013). Composting also indirectly sustains jobs in the distribution and use of compost products (Platt et al., 2013). Compost is rich in nutrients and can also reduce costs associated with synthetic fertilizer use in agriculture (Farhidi et al., 2022).
Odors coming from anaerobic decomposition landfills, such as ammonia and hydrogen sulfide, are another source of pollutants that impact human well-being, which can be reduced by aerobic composting (Cai et al., 2018).
Reducing community exposure to air pollution from landfills through composting has implications for environmental justice (Casey et al., 2021; Nguyen et al., 2023). A large review of waste sites in the United States and Europe found that landfills are disproportionately located near populations with low socioeconomic status and near racially and ethnically marginalized neighborhoods (Marzutti et al., 2010). Reducing disproportionate exposures to air pollution from landfills may mitigate poor health outcomes in surrounding communities (Brender et al., 2011)
Compost provides an important soil amendment that adds organic matter and nutrients to soil, reducing the need for synthetic fertilizers (Urra et al., 2019; U.S. EPA, 2025). Healthy soils that are rich in organic matter can benefit the surrounding ecosystem and watershed and lead to more plant growth through improved water retention and filtration, improved soil quality and structure, and reduced erosion and nutrient runoff (Bell & Platt, 2014; Martinez-Blanco et al., 2013; U.S. EPA, 2025). By reducing the need for synthetic fertilizers and by improving soils’ ability to filter and conserve water, compost can also reduce eutrophication of water bodies (U.S. EPA, 2025). These soil benefits are partially dependent on how compost is sorted because there may be risks associated with contamination of microplastics and heavy metals (Manea et al., 2024; Urra et al., 2019).
For a description of water resources benefits, please see Land Resources above.
Composting can reduce air pollution such as CO₂, methane, volatile organic compounds, and particulate matter that is commonly released from landfills and waste-to-energy systems (Kawai et al., 2020; Nordahl et al., 2020; Siddiqua et al., 2022). An analysis comparing emissions from MSW systems found composting to have lower emissions than landfilling and other waste-to-energy streams (Nordahl et al., 2020). Composting can also reduce the incidence of landfill fires, which release black carbon and carbon monoxide, posing risks to the health and safety of people in nearby communities (Nguyen et al., 2023).
Before the composting process can start, feedstocks are sorted to remove potential contaminants, including nonbiodegradable materials such as metal and glass as well as plastics, bioplastics, and paper products (Kawai et al., 2020; Perez et al., 2023; Wilson et al., 2024). While most contaminants can be removed through a variety of manual and mechanical sorting techniques, heavy metals and microplastics can become potential safety hazards or reduce finished compost quality (Manea et al., 2024). Paper and cardboard should be separated from food and green waste streams because they often contain contaminants such as glue or ink, and they degrade more slowly than other OW, leading to longer processing time and lower-quality finished compost (Kawai et al., 2020; Krause et al., 2023).
Successful and safe composting requires careful monitoring of compost piles to avoid anaerobic conditions and ensure sufficient temperatures to kill pathogens and weed seeds (Amuah et al., 2022; Ayilara et al., 2020; Cao et al., 2023; Kawai et al., 2020; Manea et al., 2024). Anaerobic conditions within the compost pile increase GHGs emitted during composting. Poorly managed composting facilities can also pose safety risks for workers and release odors, leading to community backlash (Cao et al., 2023; Manea et al., 2024; UNEP, 2024). Regional standards, certifications, and composter training programs are necessary to protect workers from hazardous conditions and to guarantee a safe and effective compost product (Kawai et al., 2020). Community outreach and education on the benefits of separating waste and composting prevent “not-in-my-backyard” attitudes or “NIMBYism” (Brown, 2015; Platt & Fagundes 2018) that may lead to siting composting facilities further from the communities they serve (Souza, et al., 2023; Liu et al., 2018).
Increased composting could positively impact annual cropping by providing consistent, high-quality finished compost that can reduce dependence on synthetic fertilizers and improve soil health and crop yields.
High-quality sorting systems also allow for synergies that benefit all waste streams and create flexible, resilient waste management systems. Improving waste separation programs for composting can have spillover effects that also improve other waste streams, such as recyclables, agricultural waste, or e-waste. Access to well-sorted materials can also help with nutrient balance for various waste streams, including agricultural waste.
Composting facilities require a reliable source of carbon-rich bulking material. Agricultural waste can be diverted to composting rather than burning to reduce emissions from crop residue burning.
Diverting OW from landfills will lead to lower landfill methane emissions and, therefore, less methane available to be captured and resold as revenue.
Composting uses wood, crop residues, and food waste as feedstocks (raw material). Because the total projected demand for biomass feedstocks for climate solutions exceeds the supply, not all solutions will be able to achieve their potential adoption. This solution is in competition with other climate solutions for raw material.
t organic waste
CO₂, CH₄
Robust collection networks and source separation of OW are vital for successful composting, but they also increase investment costs. However, well-sorted OW can reduce the need for separation equipment and allow for simpler facility designs, leading to lower operational costs. The emissions from transporting OW are not included here, but are expected to be significantly less than the avoided landfill emissions. Composting facilities are typically located close to the source of OW (Kawai et al., 2020; U.S. Composting Council [USCC], 2008), but since centralized composting facilities are designed to serve large communities and municipalities, there can be trade-offs between sufficient land availability and distance from waste sources.
We also exclude emissions from onsite vehicles and equipment such as bulldozers and compactors, assuming that those emissions are small compared to the landfill itself.
Annual generation of MSW per capita. Total global MSW generation exceeded 2 Gt/yr.
World Bank Group (2021). What a waste global database (Version 3) [Data set]. WBG. Retrieved March 6, 2025, from Link to source: https://datacatalog.worldbank.org/search/dataset/0039597
Annual generation of MSW per capita. Total global MSW generation exceeded 2 Gt/yr.
World Bank Group (2021). What a waste global database (Version 3) [Data set]. WBG. Retrieved March 6, 2025, from Link to source: https://datacatalog.worldbank.org/search/dataset/0039597
Globally, 17 countries reported composting more than 1 Mt each of organic waste in 2018, with India, China, Germany, and France reporting more than 5 Mt each (World Bank, 2018). With the exception of Austria, which composted nearly all organic waste generated, even countries with established centralized composting could divert more organic waste to composting.
The fate from which composting diverts organic waste varies from region to region, but globally over 40% of all waste ends up in landfills. Since organic waste makes up the largest percentage of MSW in most regions, excluding North America, parts of East Asia and the Pacific, and parts of Europe and Central Asia, there is ample opportunity to increase composting. In East Asia and the Pacific, South Asia, and sub-Saharan Africa, diverting organics to composting also avoids disposal in waterways and open dumps, which reduces pollution. In North America and Europe and Central Asia, 15–20% of MSW is incinerated (Kaza et al., 2018), so diverting all organic waste to composting would avoid harmful incineration emissions including CO, NOx, and VOCs (Abedin et al., 2025; Global Alliance for Incinerator Alternatives, 2019; Liu et al., 2021; Nubi et al., 2024).
Diversion of organic waste requires separation of waste streams, and cities with better collection and tracking networks often have more robust composting programs. Higher quality and more frequent reporting on waste generation and disposal worldwide could improve source separation and increase composting. Additionally, city-level and decentralized pilot programs allow for better control over feedstock collection and can bolster support for larger scale, centralized operations.
Multiple cities in Latin America and the Caribbean represent a resurgence in composting markets . In the 1960s and 1970s, composting facilities were built in cities across Mexico, El Salvador, Ecuador, Venezuela, and Brazil, but many closed due to high operational costs (Ricci-Jürgensen et al., 2020a). In 2018, 15% of waste was recycled or composted in Montevideo, Uruguay, and Bogotá and Medellín, Colombia, and 10% of waste was composted in Mexico City, Mexico, and Rosario, Argentina (Kaza et al., 2018).
Waste generation is increasing globally, with the largest increases projected to occur in sub-Saharan Africa, South Asia, and the Middle East and North Africa (Kaza et al., 2018). As waste generation doubles or triples in these regions, sustainable disposal methods will become more critical for human health and well-being.
In 2018, Ethiopia reported the highest organic waste percentage in sub-Saharan Africa at 85% of MSW, but no composting (World Bank, 2018). Organic waste percentages are high in other countries in the region, so composting could be a valuable method to handle the growing waste stream. In the Middle East & North Africa, 43% of countries reported composting as of 2018 (Kaza et al., 2018), indicating the presence of infrastructure that could be scaled up to handle increased waste in the future.
Composting reduces OW, prevents pollution and GHG emissions from landfilled OW, and creates soil amendments that can reduce the use of synthetic fertilizers (Kaza et al., 2018; Manea et al., 2024). Although we do not quantify carbon sequestration from compost use in this analysis, a full life-cycle analysis that includes application could result in net negative emissions for composting (Morris et al., 2013).
Globally, the waste sector was responsible for an estimated 3.9% of total global GHG emissions in 2023, and solid waste management represented 36% of those emissions (IPCC, 2023; UNEP, 2024). Emissions estimates based on satellite and field measurements from landfills or direct measurements of carbon content in food waste can be significantly higher than IPCC Tier 1-based estimates. Reviews of global waste management estimated that food loss and food waste account for around 6% of global emissions or approximately 2.8 Gt CO₂‑eq/yr (Wilson et al., 2024; Zhu et al., 2023). Facility-scale composting reduces emissions 38–84% relative to landfilling (Perez et al., 2023), and monitoring and managing the moisture content, aeration, and carbon to nitrogen ratios can further reduce emissions (Ayilara et al., 2020).
Unclear legislation and regulation for MSW composting can prevent adoption, and there is not a one-size-fits-all approach to composting (Cao et al., 2023). Regardless of the method used, composting converts OW into a nutrient-rich resource and typically reduces incoming waste volumes 40–60% in the process (Cao et al., 2023; Kaza et al., 2018). A comparative cost and energy analysis of MSW components highlighted that while composting adoption varies geographically and economically, environmental benefits also depend on geography and income (Zaman, 2016). Food and green waste percentages of MSW are higher in lower-resourced countries than in high-income countries due to less packaging, and more than one-third of waste in high-income countries is recovered through recycling and composting (Kaza et al., 2018).
The results presented in this document summarize findings from 22 reports, 31 reviews, 12 original studies, two books, nine web articles, one fact sheet, and three data sets reflecting the most recent evidence for more than 200 countries and territories.
Analysis of MSW in this section is based on the 2018 What a Waste 2.0 global dataset and report as well as the references cited in the report (Kaza et al., 2018; World Bank 2018). In 2018, approximately 2 Gt of waste was generated globally. Most of that went to landfills (41%) and open dumps (22%). Out of 217 countries and territories, 24 sent more than 80% of all MSW to landfills and 3 countries reported landfilling 100% of MSW. The average across all countries/territories was 28% of MSW disposed of in landfills. Both controlled and sanitary landfills with gas capture systems are included in the total landfilled percentage.
Approximately 13% of MSW was treated through recycling and 13% through incineration, but slightly more waste was incinerated than recycled per year. Incineration was predominately used in upper-middle and high-income countries with negligible amounts of waste incinerated in low- and lower-middle income countries.
Globally, only about 5% of MSW was composted and nearly no MSW was processed via methane digestion. However, OW made up nearly 40% of global MSW, so most OW was processed through landfilling, open dumping, and incineration all of which result in significant GHG emissions and pollution. There is ample opportunity to divert more OW from polluting disposal methods toward composting. Due to lack of data on open dumping, and since incineration only accounts for 1% of global GHG emissions, we chose landfilling as our baseline disposal method for comparison.
In addition to MSW, other waste streams include medical waste, e-waste, hazardous waste, and agricultural waste. Global agricultural waste generation in 2018 was more than double total MSW (Kaza et al., 2018). Although these specialized waste streams are treated separately from MSW, integrated waste management systems with high-quality source separation programs could supplement organic MSW with agricultural waste. Rather than being burned or composted on-farm, agricultural waste can provide bulking materials that are critical for maintaining moisture levels and nutrient balance in the compost pile, as well as scaling up composting operations.
Successful centralized composting starts with collection and separation of OW from other waste streams, ideally at the source of waste generation. Financial and regulatory barriers can hinder creation or expansion of composting infrastructure. Composting systems require both facilities and robust collection networks to properly separate OW from nonbiodegradable MSW and transport OW to facilities. Mixed waste streams increase contamination risks with incoming feedstocks, so separation of waste materials at the source of generation is ideal.
Establishing OW collection presents a financial and logistical barrier to increased composting adoption (Kawai et al., 2020; Kaza et al., 2018). However, when considering a full cost-chain analysis that includes collection, transportation, and treatment, systems that rely on source-separated OW can be more cost-effective than facilities that process mixed organics.
OW and inorganic waste can also be sorted at facilities manually or mechanically with automated techniques including electromagnetic separation, ferrous metal separation, and sieving or screening (Kawai et al., 2020). Although separation can be highly labor-intensive, it’s necessary to remove potential contaminants, such as plastics, heavy metals, glass, and other nonbiodegradable or hazardous waste components (Kawai et al., 2020; Manea et al., 2024). After removing contaminants, organic materials are pre-processed and mixed to achieve the appropriate combination of water, oxygen, and solids for optimal aerobic conditions during the composting process.
Regardless of the specific composting method used, aerobic decomposition is achieved by monitoring and balancing key parameters within the compost pile. Key parameters are moisture content, temperature, carbon-to-nitrogen ratio, aeration, pH, and porosity (Cao et al., 2023; Kawai et al., 2020; Manea et al., 2024). The aerobic decomposition process can be split into distinct stages based on whether mesophilic (active at 20–40 oC) or thermophilic (active at 40–70 oC) bacteria and fungi dominate. Compost piles are constructed to allow for sufficient aeration while optimizing moisture content (50–60%) and the initial carbon-to-nitrogen ratio (25:1–40:1), depending on composting method and feedstocks (Amuah et al., 2022; Manea et al, 2024). Optimal carbon-to-nitrogen ratios are achieved through appropriate mixing of carbon-rich “brown” materials, such as sawdust or dry leaves, with nitrogen-rich “green” materials, such as food waste or manure (Manea et al., 2024). During the thermophilic stage, temperatures exceeding 62 oC are necessary to kill most pathogens and weed seeds (Amuah et al., 2022; Ayilara et al., 2020).
Throughout the composting process key nutrients (nitrogen, phosphorus, potassium, calcium, magnesium, and sodium), are mineralized and mobilized and microorganisms release GHGs and heat as by-products of their activity (Manea et al., 2024; Nordahl et al., 2023). Water is added iteratively to maintain moisture content and temperature in the optimal ranges, and frequent turning and aeration are necessary to ensure microorganisms have enough oxygen. Without the proper balance of oxygen and water, anaerobic conditions can lead to higher methane emissions (Amuah et al., 2022; Manea et al., 2024). Although CO₂, methane, and nitrous oxide are released during the process, these emissions are significantly lower than associated emissions from landfilling (Ayilara et al., 2020; Cao et al., 2023; FAO, 2019; Perez et al., 2023).
Once aerobic decomposition is completed, compost goes through a maturation stage where nutrients are stabilized before finished compost can be sold or used as a soil amendment. In stable compost, microbial decomposition slows until nutrients no longer break down, but can be absorbed by plants. Longer maturation phases reduce the proportion of soluble nutrients that could potentially leach into soils.
The baseline waste management method of landfilling OW is cheaper than composting; however it also leads to significant annual GHG emissions. Composting, although more expensive due to higher labor and operating costs, reduces emissions and produces a valuable soil amendment. Establishing a composting program can have significant financial risks without an existing market for finished compost products (Bogner et al., 2007; Kawai et al., 2020; UNEP, 2024).
In 2018, Austria had the highest composting rate of 31.2%, and Vietnam composted 15% of MSW (World Bank, 2018).
For low adoption, we assumed composting increases by 25% of the existing rate or until all OW in MSW is composted. In Austria, OW made up 31.4% of MSW in 2018, so the Adoption – Low composting rate was 31.4%. In Vietnam, the Adoption – Low composting rate came out to 18.75%, which is still less than the total OW percentage of MSW (61.9%).
For high adoption, we assumed that composting rates increase by 50% of the existing rate or until all OW in MSW is composted. So high adoption in Austria remains 31.4% (i.e., all OW generated in Austria is composted). In Vietnam, the high adoption composting rate increases to 22.5% but still doesn’t capture all OW generated (61.9% of MSW).
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