What is our assessment?

Based on our analysis, decentralized composting is a “Worthwhile” solution that reduces GHG emissions while producing nutrient-rich products that improve soil health, support urban green spaces, and promote community involvement in circular waste management. 

What is it?

Decentralized composting reduces GHG emissions from landfills by diverting and locally processing OW. Composting is an aerobic biochemical process in which microorganisms break down OW into a nutrient-rich soil supplement. Since household and community waste generators are responsible for decentralized composting, this approach can also reduce transport emissions. Decentralized composting already supplements existing OW curbside collection networks in many countries, including Canada, Brazil, Sweden, India, Italy, the United States, and New Zealand (Alves et al., 2023; Bruni et al., 2020; Ricci-Jürgensen et al., 2020; Spector et al., 2026). Although on-farm composting can be part of a decentralized organic waste management system, we focus on home and community composting for this solution. 

Does it work?

There is clear evidence that aerobic decomposition from composting OW produces fewer GHG emissions than landfilling, which relies on anaerobic decomposition (Amuah et al., 2022; Manea et al., 2024) and emits methane, which is 27.9 times more effective at trapping heat than CO₂ (100-yr basis). Disposal of OW in landfills emits nearly 1.9 Gt CO₂ ‑eq (100-yr basis) of methane annually (International Energy Agency [IEA], 2024). Although composting produces CO₂, methane, and nitrous oxide, emissions can be an order of magnitude lower than landfilling (Ayilara et al., 2020; Cao et al, 2023; IEA, 2024; Nordahl et al., 2023). Widespread adoption of decentralized composting has the potential to reduce annual waste sector emissions, which accounted for 3.9% of total global GHG emissions in 2019 (Intergovernmental Panel on Climate Change [IPCC], 2023). Per-ton GHG emissions from home composting are comparable to those from centralized composting (Barrena & Sanchez, 2022; Bruni et al., 2020) although there is also evidence of lower emissions (González et al., 2024). Quantitative data on emissions from community composting sites is very limited (Sanchez et al., 2022), but still show significantly lower emissions than landfilling (de Boni et al., 2022). Most peer-reviewed literature on decentralized composting examines pilot programs with some additional case studies for commercial and institutional programs (Alves et al., 2023; de Souza & Drumond, 2022; Shen et al., 2025; Specter et al., 2026), so quantitative estimates of adoption, adoption trends, and overall climate impact are very scarce. 

Why are we excited?

Decentralized composting is affordable, supports urban green spaces, and fosters a local, circular economy with myriad socioeconomic benefits for individuals and local communities. Since it also reduces methane emissions from landfills, it also has potential to be an emergency brake solution although the global achievable impact is uncertain. Home and community composting rely on adaptable, low-cost methods that can be readily implemented and controlled to ensure high-quality compost products (Alves et al., 2023; Bruni et al., 2020; Institute for Local Self-Reliance [ILSR], n.d.; Platt, 2017; Platt & Fagundes, 2018). Decentralized composting costs less, requires less space, offers faster return on investment, and is more likely to result in compost application to soils than centralized composting (de Souza & Drumond, 2022; Spector et al., 2026), and compost quality can be as good as or better than compost produced in centralized facilities (Álvarez-Alonso et al. 2024; Alves et al., 2023; Sanchez, 2022). 

Compost use in home and community gardens or other urban green spaces is often a benefit of decentralized composting (Platt et al., 2022; Spector et al., 2026). Applying compost to soils improves soil health, nutrient supply, and water retention, and can potentially enhance carbon sequestration (Iraji et al., 2025; Martínez-Blanco et al., 2013). Reducing or eliminating collection and transportation of OW from where it’s generated to centralized facilities offers other cost and emissions savings as well (Sanchez, 2022; Shen et al 2025; Spector et al., 2026). 

Finally, decentralized composting programs stimulate local economies by supporting local organizations and fostering community (Alves et al., 2023). Community composting programs expand public awareness and education around the environmental benefits of diversion from landfills and compost application (de Souza & Drumond 2022; Shen et al., 2025; Spector et al., 2026). Well-managed community composting programs can also reduce rodent problems in urban areas (Hosain et al., 2022). Allowing for a diversity of co-existing waste processors, both centralized and decentralized, enhances the flexibility and resilience of an integrated waste collection and management system while supporting a local circular economy (Barrena & Sanchez, 2022; de Souza & Drumond, 2022).

Why are we concerned?

Successful decentralized composting requires careful source separation of OW from contaminants such as nonbiodegradable plastics, persistent monitoring of the composting process to ensure optimal conditions, and public acceptance and support. In general, home and community composting faces lower risks of contamination than centralized facilities due to better sorting (Bruni et al., 2020). Optimal composting requires carbon-rich woody biomass as well as nitrogen-rich food and yard waste, but securing sufficient carbon feedstocks can be challenging (Sanchez, 2022). In addition, smaller scale composting operations can struggle to maintain temperatures high enough to kill pathogens (Sanchez, 2022), though management practices can mitigate this risk (Bilsens Brolis & Platt, 2019; ILSR, n.d.). 

Poor management of decentralized composting programs can increase GHG emissions, odors, and safety risks, including increased rodent problems (Hosain et al., 2022), sparking community backlash. GHG emissions during composting can be minimized through precise management, especially of temperature and oxygen availability (Yasmin et al., 2022), emphasizing the importance of training and education in decentralized composting (Spector et al., 2026). Robust community outreach and education on the benefits of separating waste and safe composting methods are essential components of decentralized composting programs (Brown, 2015; Platt & Fagundes, 2018). Although community composters can generate revenue from selling compost products, direct funding through memberships or service contracts with communities and local governments results in more sustainable decentralized composting operations (Spector et al., 2026). Despite clear evidence that decentralized composting reduces GHG emissions, the lack of global adoption data and persistent social barriers limits our ability to estimate maximum achievable climate impact.

What is our assessment?

Based on our analysis, we find that fishing vessel efficiency improvements are ready to deploy and feasible, but probably have limited climate impact because the wild capture fisheries sector contributes a relatively small share of global GHG emissions. These improvements will likely provide long-term cost savings and added benefits for ecosystems and air quality. We conclude this climate solution is “Worthwhile.”

What is it?

Improving fishing vessel efficiency reduces CO₂ emissions by using gear, vessel, or operational changes that lower fuel use in wild capture fisheries. Vessel upgrades include propulsion-related changes, such as installation of more efficient engines, and non-propulsion-related alterations, such as modified bows and hulls that reduce drag. Changing to low-fuel-use gear to catch fish, when and where possible, can also reduce CO₂ emissions. Operational changes, such as speed reductions or route optimization, can likewise lead to more efficient fuel use.

Does it work?

Vessel efficiency improvements are expected to deliver substantial fuel savings. An estimated 60–90% of emissions in wild capture fisheries, which emit roughly 0.18 Gt CO₂‑eq/yr in total, likely result from fuel consumption. Speed reductions alone can reduce fuel use by up to 30%. Vessel modifications could provide fuel savings of up to 20% in small fishing vessels, which comprise roughly 86% of all motorized fishing vessels globally. Upgrading engines and other propulsion-related equipment can reduce fuel use by up to 30%. Gear switching, when viable, can also be highly effective at improving fuel use efficiency, particularly if the target species are typically caught using methods such as trawling, which has a high carbon footprint. 

Why are we excited?

The average emissions per metric ton of landed fish in wild capture fisheries have grown by over 20% since 1990, highlighting the need for efficiency improvements. Many of these improvements can be implemented without sacrificing fishing effort or opportunities, and some operational changes, such as reducing vessel speed, can be done without any new equipment. All changes reduce fuel use, saving fishers money over time and likely resulting in fewer emissions of harmful air pollutants, such as sulfur oxides and black carbon. Some upgrades could deliver additional benefits to air quality and ocean ecosystems. Cleaner engines can further reduce air pollution through more complete combustion of fuel, and gear changes could benefit seafloor ecosystems, which can be damaged from bottom fishing practices, such as trawling and dredging. Additionally, some fishing gear has high bycatch rates, and switching to gear that allows for more exclusive capture of target species can reduce waste.

Why are we concerned?

Even with widespread adoption, efficiency improvements that reduce fuel use are unlikely to have a major climate impact. Efficiency improvements could also inadvertently encourage increases in fishing effort, which would increase fuel use and offset emissions cuts. Initial costs to upgrade can be highly variable, but might be high in some cases and therefore not feasible for some fishers. Gear switching can result in lower fish catches, as some methods might not be as efficient. Some operational changes, such as reducing speeds, could lead to fishers arriving at fishing grounds late.