The role of the waste sector in the sustainable development goals and the IPCC assessment reports

The 17 SDGs and their 169 targets were investigated for their relationship between waste, landfills and waste dumps. (Sanitary) landfills are defined as managed and controlled facilities for waste disposal, whereas waste dumps are facilities, which are not controlled at all or not enough. In this study, there is a distinction between direct and indirect relationship with the SDGs. A direct relationship is understood as a direct naming of waste, landfills or waste dumps in the phrasing of the SDGs and their targets. An indirect relationship, on the other hand, is defined as a relationship not necessarily directly described in the phrasing, but stemming from a clear linkage to waste, landfills or waste dumps in a broader context. However, this term also covers the SDGs related directly. Most authors do not differentiate between the direct and indirect relationship. The indirect relationship was assessed based on the authors’ expertise and consequently compared to 14 recent literature studies.

The IPCC report series from 1990 to 2023 (six in total) were examined for the evolution of waste management strategies, particularly their sections addressing waste-related topics and mitigation strategies.

The IPCC issues various documents differing mainly structure-wise and giving variable emphasis on certain topics. This study is based on information obtained from diverse types of documents ranging from Summaries for Policymakers, Technical Summaries to full assessment reports. Higher attention was paid to the reports by Working Group III containing potential mitigation options. In case of the Second Assessment Report (SAR), working groups were exceptionally restructured and mitigation options were proposed in the assessment report by Working Group II.

According to numerous studies, the waste sector is generally considered to have an important position in achieving the SDGs (Alam et al. 2022; Calderón Márquez et al. 2019; Castellani et al. 2022; Huber-Humer 2022; ISWA 2023; Mavropoulos et al. 2016; Roy et al. 2023; Ye et al. 2023; Zhang et al. 2023). Conversely to that, the SDGs accelerated research in the field of municipal solid waste management and also encouraged the transition of innovations’ focus on sustainable and circular methods in the sector (Ye et al. 2023). The importance of proper waste management is visible especially in low-income countries, because these tend to grapple with the lack of effective solid waste management, which inevitably causes diverse negative impacts (Castellani et al. 2022).

In terms of a direct relationship between waste management and the SDGs, out of 169 targets and 17 SDGs, only six targets included in four SDGs mention waste (see Fig. 1). The SDGs directly addressing waste are SDG 6 Clean water and sanitation, SDG 11 Sustainable cities and communities, SDG 12 Responsible consumption and production and SDG 14 Life below water.

The SDG’s target 6.3 addresses elimination of waste dumping to achieve an effect on water quality. SDG 11.6 relates to solid waste collection and management. SDG 12.3 focuses on food waste and SDG 12.4 on hazardous waste, its generation and management. SDG 12.5 demands minimization of waste generation through prevention, reduction, recycling and reuse, while SDG 14.1 deals with plastic debris density in marine habitats.

The number of SDGs relating indirectly to waste, is substantially higher. In this study, 11 SDGs were found to be relevant to landfills and waste dumps, these were SDGs 1, 2, 3, 6, 7, 8, 11, 12, 13, 14 and 15. Due to the complexity of waste management, it is difficult to distinguish between the relationship based solely on landfills and waste dumps or on waste management in general. Other studies found the waste sector to be indirectly related to 5–17 SDGs (Alam et al. 2022; Castellani et al. 2022; Huber-Humer 2022; IPCC 2022; Lohani et al. 2021; Puntillo 2023; Roy et al. 2023; Sallwey et al. 2017; Thacker et al. 2019; United Nations 2018). A comparison of literature sources tackling the issue of SDG’s connection to the waste sector is summarized in the Supplementary Material 1.

Certain SDGs were evaluated as relevant to the waste sector by most authors and also by the authors of this study—these are: SDG 6 Clean water and sanitation (12 out of 15 studies), SDG 12 Responsible consumption and production (14 out of 15 studies), and SDG 15 Life on land (12 out of 15 studies) (Alam et al. 2022; Calderón Márquez et al. 2019; Castellani et al. 2022; Huber-Humer 2022; IPCC 2022; Lohani et al. 2021; Mavropoulos et al. 2016; Puntillo 2023; Roy et al. 2023; Sallwey et al. 2017; Thacker et al. 2019; United Nations 2018; Zhang et al. 2023). The SDG assessed as relevant by all literature sources was SDG 11 Sustainable cities and communities (15 out of 15 studies) (Alam et al. 2022; Calderón Márquez et al. 2019; Castellani et al. 2022; Huber-Humer 2022; IPCC 2022; Lohani et al. 2021; Mavropoulos et al. 2016; Puntillo 2023; Roy et al. 2023; Sallwey et al. 2017; Thacker et al. 2019; United Nations 2018; Zhang et al. 2023). Based on this finding, SDGs 6, 11, 12 and 15 are perceived as significantly connected to waste management and actions in the waste sector have profound effects on them.

One of the SDGs, that was not perceived as relevant to the waste sector by the majority of studies, but was found to be relevant by the authors of this study, is SDG 2 Zero hunger (IPCC 2022; Mavropoulos et al. 2016; Roy et al. 2023; Sallwey et al. 2017; Thacker et al. 2019). Proper resource management can assure that edible food will be utilized by people instead of being wasted in landfills or elsewhere. Furthermore, proper waste management may support composting and the production of high-quality composts, which may consequently support agriculture.

A study by Thacker et al. (2019) investigated the relationship between SDGs and solid-waste infrastructure distinguishing between direct and indirect relationships. The directly linked SDGs have references to waste generation and management or pollution of marine and terrestrial ecosystems caused by debris and dumping. Findings of Thacker et al. (2019) in terms of direct relationship are aligned with the ones in this study except for SDG 9 Industry, innovation and infrastructure. This discrepancy results from the focus of the study on solid-waste infrastructure.

It has to be noted that there are differences in the perception of the relationship between the SDGs and waste sector among various subjects or entities, as described by Zhang et al. (2023). For example, construction and demolition waste management relates to various SDGs. While academic literature addresses mainly SDGs 7, 8 and 14, industrial innovation facilitates SDGs 3, 9 and 15. SDGs 6, 11 and 12 were priorities for both, academia and industry (Zhang et al. 2023).

Even though all 17 SDGs share the same goal, there can be trade-offs between them, as described by Gusheva et al. (2022). For example, the formalization of the recycling sector is beneficial for SDG 8 Decent work and economic growth and SDG 3 Good health and well-being. On the other hand, it might bring trade-offs for SDG 1 No poverty. Informal workers can be negatively affected by the formalization of waste management, which may cause a decrease in their income and an increase in the chances of falling into poverty. However, the synergies generally prevail (Gusheva et al. 2022).

The IPCC also acknowledges the connection between the SDGs and the waste sector. For example, according to the Sixth Assessment Report (AR6), “Waste prevention, minimisation and management” as a mitigation option relates to almost all SDGs (Pathak et al. 2022).

Landfilling has an important role in the waste sector based on a strong representation in global waste management. Therefore, landfills and waste dumps in particular are connected to SDGs. A few studies declare the relationship between landfills and waste dumps and the SDGs, see Supplementary Material 1.

The only SDG directly targeting landfills or waste dumps is the SDG’s target 6.3, which addresses the elimination of dumping in order to improve water quality. When looking at the broader context of the SDGs, there are more connections between landfills and waste dumps.

SDG 13 Climate action is relevant to landfills and waste dumps, but it does not directly mention them. However, none of the sectors are addressed directly, the related indicator 13.2.2 is defined very broadly, unlike SDG 6 Clean water and sanitation. The indicator addresses “Total greenhouse gas emissions per year” (United Nations 2023) which, however, clearly emphasizes the connection to methane emitted from landfills and waste dumps.

In this study, 11 SDGs and 29 targets out of 17 and 169, respectively, were assessed as indirectly relevant to landfills and waste dumps. Only few other studies examined the relationship between landfills and the SDGs as illustrated in Fig. 2 and Supplementary Material 1. Mavropoulos et al. (2016) concluded that closure of waste dumps would be beneficial for all 17 SDGs, while Calderón Márquez et al. (2019) found landfill mining to be relevant for 10 SDGs—SDGs 1, 3, 6, 7, 8, 11, 12, 13, 14, 15. Landfill mining is a process, which can provide valuable resources by extracting minerals or other solid natural resources that have been disposed (Krook et al. 2012). In contrast, Castellani et al. (2022) emphasized the linkage with only four SDGs, namely SDGs 6, 11, 14 and 15, by analysing the impact on the SDGs from landfilling, open dumping and open burning avoidance in low-income countries.

The EU-waste hierarchy is a sequence of actions in the order of their preferability in the context of environmental impact (Cecere et al. 2023). It suggests that the society should treat waste or materials in the given order. However, a deviation from this framework can be justifiable if given proper information on life cycle thinking and the waste’s overall impact (European Commission 2019).

The changes in the waste sector’s role in the IPCC assessment reports are illustrated in Fig. 3 using the waste hierarchy pyramid, the graphic is based on a figure published in the AR5 by the IPCC (IPCC 2014). Figure 3 differentiates between main focus and main mitigation options in the field of waste management in the respective reports. Thereby, it visualises the shift of priority in the waste hierarchy in a clear and concise manner. Moreover, it shows the SDGs directly linked to particular steps of the hierarchy, which comprises SDGs 6, 11, 12 and 14. More indirect connections, which are not demonstrated in Fig. 3 could be found, for example, SDG 7 Affordable and clean energy is indirectly connected to “Energy recovery” or “Landfill with CH₄ Recovery and Use”. Landfills are strongly connected to SDG 13 due to methane emissions as demonstrated in Fig. 2.

According to the observation in this study, the perception of the waste sector in the IPCC assessment reports changes. Landfilling as a disposal strategy is relevant in all reports. Landfills and waste dumps play an important role in climate change given the fact that they are significant sources of a strong GHG—methane. Landfills with methane flaring are listed as a mitigation option in the First Assessment Report (FAR), whereas landfilling without the use of emitted gases is not being seen as an acceptable approach that can mitigate climate change. When landfills are equipped with technologies that enable gas recovery and use, they become a relevant mitigation option in all IPCC assessment reports, comparably to energy recovery of waste during waste incineration.

All reports perceive recycling as an important mitigation option. Re-use becomes more relevant in the latter reports, especially in the last three of them. Waste avoidance and reduction is seen as a relevant approach from the beginning of the IPCC assessment reports, but it receives higher attention in the last three reports.

Many mitigation options in waste management that were listed in older reports remain important, but they tend to be extended with more options that are often indirect and more complex. Initially, mainly technological mitigation options were relevant, later also the non-technological ones started to be essential, e.g., behavioural changes such as reduction of demand and choice of products (Pathak et al. 2022).

The ISWA addresses the lack of attention paid to the waste sector’s relevancy, claiming that the waste and resource management is being neglected in the global climate strategy (ISWA 2023).

The role of waste sector cannot be perceived only as a role of a polluter but also as a necessary tool and a positive contributor to climate protection (Obersteiner 2021). The waste sector can partially contribute to climate change mitigation and may have positive effects on energy, forestry, agriculture, etc. (United Nations Environment Programme 2010). Wilson (2023) also claims that improvements in waste and resource management can significantly mitigate global heating. In other words, waste is considered both an environmental problem and a solution/resource (Roy et al. 2023).

Analogous to the perception of waste management in the IPCC assessment reports, also the role of landfills and waste dumps changed in the course of time. Landfills were highly relevant in the first assessment reports, because methane emissions from landfills strongly contribute to climate change. This was seen as the main impact to which the most attention should be paid to. The reports focused on landfills and mitigation options were directly addressing them. In latter reports, the GHGs emissions slightly increased (see Table 1), but the question of waste management’s effects on the environment and climate becomes more complex. Mitigation options become more indirect, as they focus on waste reduction rather than methane utilization, moving from exclusively technical solutions towards transdisciplinary approaches.

A simple factor was determined to show the relevance of landfills and waste dumps in the IPCC report series. The factor was calculated dividing the sum of certain key words (landfill- and dump-) by the sum of pages of the full IPCC assessment reports, see Fig. 4. The counts of the key words and pages are summarized in the Supplementary Material 2. Landfills and waste dumps remain relevant to climate change, yet they seem to attract less attention in the recent IPCC assessment reports according to the factor. The factors’ increase in the AR4 can be attributed to an additional chapter solely dedicated to post-consumer waste (Chap. 10), while the factors’ decrease in the latest report is caused by declining attention to landfills and waste dumps in terms of mitigation options. Profoundly higher emphasis is put on waste avoidance, which is the opposite strategy in the waste hierarchy triangle. The word waste is becoming to be substituted by the word resource.

However, waste dumps remain a dominant waste management strategy mainly in developing countries, whereas they have been fully replaced by engineered sanitary landfills in developed countries (Mavropoulos et al. 2016). Globally, 33% of waste is still disposed in waste dumps, 8% in sanitary landfills without gas collection, and 4% of waste is disposed in controlled landfills. According to Manfredi et al. (2009), up to 1000 kg CO₂-eq tonne⁻¹ are produced by open dumps, 300 kg CO₂-eq tonne⁻¹ by conventional landfills of mixed waste and 70 kg CO₂-eq tonne⁻¹ by low-organic-carbon waste landfills.

Despite the decreasing attention to landfills and waste dumps, methane emissions from the waste sector and landfills in particular have been increasing on a global scale according to the IPCC reports (Table 1 and further demonstrated in Fig. 5).

The waste sector is the largest contributor to the urban share of GHG emissions after the energy sector (Lwasa et al. 2022). Moreover, landfills remain to be one of the strongest anthropogenic sources of methane, both compared to other sectors (namely placed third compared to agriculture and fossil fuel mining and distribution) (Toha and Rahman 2023), and within the waste management sector itself. For comparison, according to data from the AR4, estimated emissions from waste incineration were around 50 MtCO₂-eq/yr in 2005. In the same year, the emissions from landfills were approximately tenfold (Bogner et al. 2008).

It is necessary to emphasize that the situation differs greatly worldwide. For example, the GHGs emissions from waste sector have fallen by 42% in the EU between the years of 1995–2017 (Eurostat 2023). This decrease was caused by the increase in landfill gas recovery and the decrease in landfilling. However, this tendency does not apply to other countries and continents where the emissions from landfills continue to rise, as visualised in Fig. 5.

Even though the landfill-GHGs generation has been decreasing in North America, Europe and Central Asia, local landfills remain to be the strongest sources both in total amount and in terms of per capita emissions. The South Asian region, on the other hand, has the lowest per capita landfill-GHGs emissions. This is linked to the level of economic development of the regions, which tends to be a key factor in terms of waste generation and consequently to GHGs generation. Higher income is linked to higher GHGs emissions according to Zhao et al. (2019) and US EPA (2012). In developing countries, the GHGs emissions from landfills are rising and are expected to rise in future (Mavropoulos et al. 2016). The GHGs emissions in high-income countries have to keep decreasing, and adequate measures have to be applied to recover the emitted gas in the low/lower middle-income countries and to reduce its generation.

In 2017, waste was the EU’s fourth largest source sector with 3% share of total GHG emissions (Eurostat 2023). However, the AR4 listed the waste sector as a “small contributor” to global GHGs emissions, with a share of less than 5% (IPCC 2007). For comparison, global aviation accounted for 2% of energy-related CO₂ emissions in 2022 (International Energy Agency 2023).

It has to be noted that data regarding waste sector are often difficult to obtain, including the data regarding methane emissions. Some assessment reports list data for landfill-related emissions only, but others list them in broader categories, as seen in Table 1.