Curbing Global Solid Waste Emissions Toward Net-Zero Warming Futures
Kok Sin Woon
Xiamen University Malaysia
DOI: https://doi.org/10.25453/fpprize.28723997.v1
Winning article: Curbing global solid waste emissions toward net-zero warming futures (Science, 2023)
“To meet Paris targets, the global solid waste sector needs abrupt intervention. Existing technologies are available, but we must act fast.”
The global solid waste management system contributes to methane (CH₄) emissions, a potent greenhouse gas (GHG) with a global warming potential 84 times that of CO₂ over 20 years. In 2022, atmospheric CH₄ levels reached 191.8 parts per billion, more than twice the preindustrial levels, with solid waste sectors accounting for around 20% of anthropogenic CH₄ emissions. Activities like open dumping and poorly managed landfills worsen CH₄ emissions. If prompt action is not implemented, emissions related to municipal solid waste (MSW) are expected to nearly double by 2050 compared to 2016.
Our research was driven by the lack of a comprehensive study linking solid waste emissions with the Paris Agreement’s goals for 1.5°C and 2°C pathways, as well as the Global Methane Pledge, which aims for a 30% reduction in CH₄ emissions by 2030, based on a 2020 baseline. Our paper addresses a critical gap in understanding the CH₄ flow affecting the short-term warming effect in the solid waste industry. We focused on this industry as it is often overlooked, but is one of the highest methane-emitting sectors and has significant CH₄ reduction potential. We predicted the aggregated GHG emissions of the global MSW system to evaluate its capacity to mitigate global warming and achieve climate targets. Our findings indicated that the current MSW system is projected to exceed the emissions budget for the 1.5°C target between 2028 and 2029 and the 2°C target between 2038 and 2043.
Given that the global MSW system would exceed the emissions budget under business-as-usual conditions, our research identifies four key mitigation strategies to reduce GHG emissions across income groups: (i) retrofitting landfills with landfill gas capture, (ii) diverting organic waste for composting, (iii) diverting organic waste for anaerobic digestion, and (iv) halving waste generation. These strategies could cut cumulative GHG emissions by 33–72% compared to business-as-usual, with anaerobic digestion (72% reduction) and halving waste (68%) leading the way. The effectiveness of these mitigation strategies varies by income group. For high-income countries, halving waste generation is the most effective approach, given the high rates of non-biodegradable waste (e.g., plastics and packaging). For other income groups, diverting organics to anaerobic digestion presents the most effective strategy due to higher biodegradable waste volumes.
Another key finding in our research is that staying within the 1.5°C limit requires adopting more than one strategy because individual strategies alone are insufficient. An integrated MSW framework encompassing multiple strategies to tackle the heterogeneity of MSW composition will result in a more adaptable approach to reducing GHG emissions. Adopting all three strategies, retrofitting landfills, composting, and halving waste, could achieve a net-zero warming waste system by 2050 relative to 2020. Upon the complete adoption of mitigation strategies by 2050, CH4 emissions can be reduced by up to 80% compared to the business-as-usual scenario. However, the designed mitigation strategies will not be able to reduce 30% of the CH4 emissions from the global MSW system in a timely manner by 2030 relative to 2020. We found that it is necessary to accelerate the complete adoption of mitigation strategies by at least 9 to 17 years (by 2033 to 2041) to be on track with the progress needed to achieve the Global Methane Pledge under a linearly decarbonizing future.
Our research connects directly with the climate change boundary, where CH4 reductions from MSW systems provide immediate cooling for countering near-term warming. We offer MSW management strategies based on a data-driven approach to formulate sustainable CH4 flow and nutrient cycling of organic waste, enhancing biogeochemical flows and reducing land use change in the waste-to-resource mechanism. Integrating MSW reduction into the circular economy implementation minimizes resource extraction and reduces pressure on planetary systems.
Fingure 1. Our paper was featured on the Science cover
The identified mitigation potential is a focal point that captures attention and fosters awareness, which is crucial to initiating and launching effective MSW management policies. We have outlined a timely blueprint for its integration into sustainable MSW policies and commercial practices. Our research provides a benchmark for countries regarding the necessary waste minimization rate and the volume of MSW that should be treated biologically. Our proposed MSW management practices are scalable for widespread implementation. They are designed for countries at various income levels to ensure stakeholders can prioritize effective strategies based on their unique circumstances.
Our findings highlight the need for a cohesive mix of three categories of policy tools to expedite this transition: (i) direct regulation, which includes laws that are strictly enforced; (ii) economic instruments that provide incentives and disincentives for specific solid waste management practices; and (iii) social tools based on communication and engagement with stakeholders. Our results display the essential role of the global solid waste system as a catalyst for keeping our planet within its planetary boundaries. Government institutions should collaborate with environmental consultants and policy analysts to conduct feasibility studies, select MSW treatment sites, and develop policy proposals for implementing these mitigation strategies. When governments and companies adopt sustainable MSW management practices, they set an example for communities. This moral obligation extends to individuals, encouraging them to change their consumption and disposal patterns in favor of sustainability.
The specific design and implementation of incentives must be tailored to each country's socioeconomic context to ensure equitable access to MSW-related mitigation practices. Charging systems used in high-income countries (e.g., flat rates and the “pay-as-you-throw” system) collect funds to finance advanced treatment services and provide an incentive for MSW reduction. International funding (e.g., World Bank development loans) and decentralized solutions (like community composting) are essential for lower-middle-income and low-income countries.
The future of planetary health hinges on our actions today. Our key message is simple: waste disposal and treatment technologies are available. What remains is our collective will to act, and we must act quickly.
Figure 2: From the top left corner: Zheng Xuan Hoy, Vincent Kok Sin Woon, Wen Cheong Chin, Yee Van Fan, and Seung Jick Yoo.