Post-consumer waste is a small contributor to global greenhouse gas (GHG) emissions (<5%) with total emissions of approximately 1300 MtCO2-eq in 2005. The largest source is landfill methane (CH4), followed by wastewater CH4 and nitrous oxide (N2O); in addition, minor emissions of carbon dioxide (CO2) result from incineration of waste containing fossil carbon (C) (plastics; synthetic textiles) (high evidence, high agreement). There are large uncertainties with respect to direct emissions, indirect emissions and mitigation potentials for the waste sector. These uncertainties could be reduced by consistent national definitions, coordinated local and international data collection, standardized data analysis and field validation of models (medium evidence, high agreement). With respect to annual emissions of fluorinated gases from post-consumer waste, there are no existing national inventory methods for the waste sector, so these emissions are not currently quantified. If quantified in the future, recent data indicating anaerobic biodegradation of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in landfill settings should be considered (low evidence, high agreement).
Existing waste-management practices can provide effective mitigation of GHG emissions from this sector: a wide range of mature, environmentally-effective technologies are available to mitigate emissions and provide public health, environmental protection, and sustainable development co-benefits. Collectively, these technologies can directly reduce GHG emissions (through landfill gas recovery, improved landfill practices, engineered wastewater management) or avoid significant GHG generation (through controlled composting of organic waste, state-of-the-art incineration and expanded sanitation coverage) (high evidence, high agreement). In addition, waste minimization, recycling and re-use represent an important and increasing potential for indirect reduction of GHG emissions through the conservation of raw materials, improved energy and resource efficiency and fossil fuel avoidance (medium evidence, high agreement).
Because waste management decisions are often made locally without concurrent quantification of GHG mitigation, the importance of the waste sector for reducing global GHG emissions has been underestimated (medium evidence, high agreement). Flexible strategies and financial incentives can expand waste management options to achieve GHG mitigation goals – in the context of integrated waste management, local technology decisions are a function of many competing variables, including waste quantity and characteristics, cost and financing issues, infrastructure requirements including available land area, collection and transport considerations, and regulatory constraints. Life cycle assessment (LCA) can provide decision-support tools (high evidence, high agreement).
Commercial recovery of landfill CH4 as a source of renewable energy has been practised at full scale since 1975 and currently exceeds 105 MtCO2-eq, yr. Because of landfill gas recovery and complementary measures (increased recycling, decreased landfilling, use of alternative waste-management technologies), landfill CH4 emissions from developed countries have been largely stabilized (high evidence, high agreement). However, landfill CH4 emissions from developing countries are increasing as more controlled (anaerobic) landfilling practices are implemented; these emissions could be reduced by both accelerating the introduction of engineered gas recovery and encouraging alternative waste management strategies (medium evidence, medium agreement).
Incineration and industrial co-combustion for waste-to-energy provide significant renewable energy benefits and fossil fuel offsets. Currently, >130 million tonnes of waste per year are incinerated at over 600 plants (high evidence, high agreement). Thermal processes with advanced emission controls are proven technology but more costly than controlled landfilling with landfill gas recovery; however, thermal processes may become more viable as energy prices increase. Because landfills produce CH4 for decades, incineration, composting and other strategies that reduce landfilled waste are complementary mitigation measures to landfill gas recovery in the short- to medium-term (medium evidence, medium agreement).
Aided by Kyoto mechanisms such as the Clean Development Mechanism (CDM) and Joint Implementation (JI), as well as other measures to increase worldwide rates of landfill CH4 recovery, the total global economic mitigation potential for reducing landfill CH4 emissions in 2030 is estimated to be >1000 MtCO2-eq (or 70% of estimated emissions) at costs below 100 US$/tCO2-eq/yr. Most of this potential is achievable at negative to low costs: 20–30% of projected emissions for 2030 can be reduced at negative cost and 30–50% at costs <20 US$/tCO2-eq/yr. At higher costs, more significant emission reductions are achievable, with most of the additional mitigation potential coming from thermal processes for waste-to-energy (medium evidence, medium agreement).
Increased infrastructure for wastewater management in developing countries can provide multiple benefits for GHG mitigation, improved public health, conservation of water resources, and reduction of untreated discharges to surface water, groundwater, soils and coastal zones. There are numerous mature technologies that can be implemented to improve wastewater collection, transport, re-use, recycling, treatment and residuals management (high evidence, high agreement). With respect to both waste and wastewater management for developing countries, key constraints on sustainable development include the local availability of capital as well as the selection of appropriate and truly sustainable technology in a particular setting (high evidence, high agreement).