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The International Institute for Applied Systems Analysis (IIASA), in collaboration with its Japan National Member Organization (NMO), supported by Ministry of the Environment Japan (MOEJ) has initiated a joint research endeavor centered on Cities Transformation. The primary aim of this collaborative effort's inaugural phase is the compilation of a fast-track comprehensive report. This report aims to consolidate the current understanding of urban transformations, identifying critical knowledge gaps therein. It serves to support the scientific community, city stakeholders, and policy-makers in discerning areas warranting greater attention and, crucially, further investigation and study. Particularly, it provides updates on the IPCC 7th Assessment Cycle, with a specific focus on its Special Report on Climate Change and Cities. Commencing with an overview of global urbanization trends, the report delves into the status of informal urban settlement development (Section 2). Subsequently, it comprehensively discusses the physical aspects of climate change, including impacts, vulnerability, adaptation, and mitigation, with a spotlight on air pollution and waste challenges (Section 3). Section 4 shifts focus to systems transformation, examining sectors and cross-cutting perspectives through various case studies. Following this, Section 5 investigates the enabling conditions for city transformations, emphasizing the roles of governance, behavioral and lifestyle changes, innovation and technology, and finance. Expanding further, Section 6 assesses the synergies and trade-offs of mitigation and adaptation strategies, with a particular lens on Sustainable Development Goals (SDGs), health, and well-being. The report concludes by recognizing significant knowledge gaps highlighted through expert insights.

South Asia is a global hotspot of air pollution, harboring 37 of the world's 40 most polluted cities. Sixty percent of its residents inhabit areas characterized by high pollution levels, where concentrations of fine particulate matter (PM2.5) - accountable for chronic respiratory diseases and over two million premature deaths annually in the region - surpass the least stringent air quality standard set by the World Health Organization (WHO). Addressing this problem with fragmented approaches is unlikely to yield significant results, as air pollution extends beyond geographical boundaries. Even if fully executed, existing policy measures will only offer partial relief in diminishing PM2.5 concentrations in South Asia. This study aims to identify and map air pollution hotspots in South Asia in terms of concentration and exposure, understand the various sources of pollution in hotspot areas, and help categorize policy actions and interventions based on a systematic analysis of costs and benefits using the GAINS modeling framework. A large variety of emission sources contribute to PM2.5 pollution in ambient air therefore, effective air quality management needs to balance measures across these sources. Our results reveal that the current environmental policies will decouple emissions from economic growth, however, will not be sufficient to deliver large reductions in ambient PM2.5 in the South Asia region. There is scope for further measures beyond current policies that could approach the WHO Interim Targets (35 µg/m3) for PM2.5. Finally, cost-optimal strategies for air quality management can achieve significant cost savings compared to conventional approaches; however, they require cooperation within states, regions and countries in South Asia. Monitoring of the chemical composition of PM2.5 reveals that a significant share of total fine particulate matter in ambient air in South Asia is composed of secondary particles, i.e., particles that are formed in the atmosphere

The need for improved waste management systems has gained momentum globally in order to work towards the reduction of GHG emissions and the impact it has on global climate change. In South Africa, the disposal of unsorted waste to landfill is still the primary waste management method across the country; however, legislative developments aim to drive integrated waste management and the circular economy, putting the disposal of waste to landfill as the least favorable waste management solution. With 80% of the municipal solid waste ending up in landfill sites unsorted and untreated, the only reasonable “activator” of the circular economy would be an integrated waste management system, which is underpinned by an efficient separated collection at the source, followed by carefully selected and strategically localized waste treatment strategies, decentralized recycling facilities, and sustainable end-of-life disposal options. The Waste Resource Optimization and Scenario Evaluation (WROSE) model was developed to assist municipalities in aligning with national legislative requirements and achieving zero waste. This will be achieved through the application of the waste hierarchy into municipal solid waste management practices as well as through the promotion of the circular economy. The WROSE model/decision-making tool is a multiple scenario optimization model that analyzes and evaluates the feasibility of waste management strategies upon all four levels of sustainability (environmental, economic, social and institutional). One of the key gaps identified is lack of application of the WROSE model as a comprehensive zero waste model on South African municipalities with updated waste characterization data; this study addresses the gap identified, by presenting the results of the successful activation of circular economy and integrated waste management in South African case study municipalities. The WROSE model was applied to several metros for problem waste streams such as C&D

The global anthropogenic emissions of air pollutants including sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3), particulate matter (distinguishing PM2.5, PM10, BC, OC, OM), non-methane volatile organic compounds (VOC), carbon monoxide (CO), and methane (CH4) were developed at CIAM/IIASA[2]. These emission datasets have been produced with the GAINS model[1] (Amann et al., 2011) within work under UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP) and cover the 1990-2050 period. The respective emission datasets consist of 5-yearly global annual and monthly emissions and include two to three scenarios, depending on the version of the dataset: a baseline that is referred to as current legislation case (LRTAP Baseline), a scenarios exploring technical mitigation potential for all pollutant species (LRTAP MTFR), and a scenario that combines climate policy, behavioral changes, and strong technical mitigation of all pollutants (LRTAP LOW) Brief explanation of assumptions used in these three scenarios. The current legislation scenario (LRTAP Baseline) assumes implementation and effective enforcement of all committed energy and environmental policies affecting emissions of air pollutants and greenhouse gases. CIAM has undertaken a review and update of historical data (up to 2020) driving emissions of all species in the GAINS model, drawing on the statistical information from EUROSTAT, International Energy Agency (IEA), UN Food and Agriculture Organization (FAO), as well as reporting of data and emissions to the Center on Emission Inventories and Projections[3]. For the EU27, the energy and agriculture projections are consistent with the objectives of the European Green Deal and Fit for 55 package making EU carbon neutral by 2050; these are consistent with the projections used in the EU third Clean Air Outlook [4]. For West Balkan, Republic of Moldova, Georgia, and Ukraine, a similar set of modelling tools was used as for the EU developing a new consi

Recent trajectories of production and consumption patterns have resulted in massively rising quantities of municipal solid waste (MSW). Building on the Shared Socioeconomic Pathways, we build two sets of global scenarios until 2050, namely baseline and mitigation scenarios. We assess trajectories of future MSW generation and the impact of MSW management strategies on methane and air pollutant emissions. In 2050, the adoption of mitigation strategies in the sustainability-oriented scenario yields earlier, and major, co-benefits compared to scenarios in which inequalities are reduced but that are focused solely on technical solutions. In 2050, the GHG emissions in the sustainability-oriented scenario amount to 182 Gg CO2eq/yr of CH4, to be released while particulate matter, and air pollutants from open burning of MSW can be virtually eliminated. We demonstrate that the 6.3 target of the SDG 6 can only be achieved through more ambitious sustainability-oriented scenarios that limit MSW generation and improve management.