Cities increasingly pledge net-zero emissions targets, but the robustness of their residual emissions strategies remains uncertain. We examine the approaches of 103 European cities aiming at net zero by 2030. Total residual emissions are 61.4 MtCO2e originating mostly from buildings and transport, with the median at 0.8 tCO2e per capita, indicating a rapid decarbonization process. All municipal strategies rely on temporary, land-based CO2 removal, then carbon credits (40%) and permanent CO2 removal (32%). We develop the residual emissions strategy robustness index to assess the robustness of compensation strategies, indicating that the current maturity is medium-low with notable geographical disparities. Although cities invest in options mapping and governance, little attention is paid to land availability, the potential of the urban fabric to become a distributed carbon sink, provisions against carbon reversals, monitoring, timing and quantification (estimates cover only 18% of total residual emissions). We also distil recommendations and best practices to address residual emissions.

Amidst escalating climate impacts and continued emissions, numerous case studies have examined how cities can mitigate and adapt to climate change. Yet, systematic cross-sectoral and cross-impact assessments that identify which climate actions are relevant to which types of cities remain limited. This study addresses this gap for Europe through a data-driven analysis of European cities, categorising them into four distinct city types ( Shrinking cities, Growing cities, Established cities, Metropolises ), quantitatively analysing their need and capacity to act on climate change, and providing a systematic overview of effective climate action strategies for each of these clusters. Based on harmonised data for all 1263 cities in Europe, we identify sectoral and climate impact hotspots requiring concerted climate action across the four city types. These include reducing building- and transport-related greenhouse gas emissions in Metropolises and Established cities , heat and drought risk in Growing cities , and flood risk in Shrinking cities . Drawing on the existing case study literature comprising 1613 climate action assessments, we provide context-specific recommendations for addressing these climate hotspots and unlocking co-benefits by overcoming reported implementation challenges such as limited finance, local governance capacity, behavioural inertia and distributional conflicts. We further outline research gaps for more actionable knowledge on urban climate mitigation and adaptation with regards to scope of cities covered, kinds of actions assessed, and quality of evaluations performed. Together, these insights can inform cross-city learning and targeted policy and investment prioritisation across urban planning, public services, technology deployment or governance capacity in line with local contexts.

This study investigates the spatial relationship between renewable energy potential, economic prosperity, and the establishment of Positive Energy Districts (PEDs) across European regions. PEDs are connected clusters of buildings that generate a surplus of renewable energy on a yearly basis through local energy production and consumption, energy storage, and direct management of renewable energy sources. Beyond their technical contribution to energy transitions, PEDs are also positioned as mechanisms for economic development, energy citizenship, democracy, and energy justice. While existing literature has predominantly focused on the technical dimensions of PEDs (e.g., energy efficiency, renewables, flexibility), little attention has been devoted to their territorial dimensions, specifically, where PEDs are implemented and under what local conditions they emerge. This study aims to investigate whether PEDs are more frequently installed in areas with higher GDP per capita and/or renewable energy potential compared to non-PED areas. A comparative analysis using descriptive statistics and non-parametric tests indicates that PEDs are primarily concentrated in areas with high GDP per capita, but not necessarily in regions with high renewable energy potential. These findings underscore the need to investigate further on the enabling conditions which shape the design and geographic distribution of PEDs, ensuring that their benefits extend beyond high-income regions.

Leading European cities race to reach net-zero emissions, but residual emissions are tied to easier-to-abate sectors and temporary, land-intensive carbon removal for compensation. To keep climate neutrality credible and fair, policy must tighten expectations on cutting emissions and set clear rules for carbon removal and credits.

Cities are pivotal in the global quest for climate neutrality, yet implementation of climate actions often lags behind their ambitions. This Perspective distils practical recommendations to unlock the full potential of cities on their zero-emission journey. It focuses on comprehensive emissions accounting, innovative green finance, multilevel governance, co-creation, and integrated urban planning. These are key areas to bridge the ambition-implementation gap and advance a fair, inclusive climate transition.

This study investigates the alignment of climate change mitigation with air quality initiatives in 362 (mostly European) cities eligible under the Climate-Neutral and Smart Cities Mission, hence targeting net-zero greenhouse gas (GHG) emissions by 2030. It examines ambient air quality, particularly PM 2.5 concentration levels, and GHG emissions, considering physical attributes, policy frameworks, and local authority actions. The research finds a north-to-south gradient in air quality, with northern cities exhibiting better air conditions, and a strong correlation between sectors contributing to GHG emissions and air pollution. Cities' strategies are dominated by cross-sectoral plans and assessing air quality as a co-benefit of climate mitigation is common practice, suggesting potential for synergistic approaches to climate and air quality goals, supported by the political authority that cities typically exert over relevant policy areas. Machine learning analysis (XGBoost) highlights national context, population density, and climate class as significant predictors of PM 2.5 levels, with policy variables indicating that proactive health and justice measures in city governance may correlate with improved air quality. The study advocates for a co-benefits approach in urban policy-making to effectively address climate change and air quality challenges, and it emphasises the need for transdisciplinary research and governance to optimise outcomes and reduce trade-offs.

Achieving climate neutrality demands effective urban climate governance and stakeholders' mobilisation. This study conducts a comprehensive analysis of 362 cities' Expressions of Interest (EOI) submitted for the European Climate-Neutral and Smart Cities Mission to examine the prevalence and nature of stakeholder engagement in urban climate action. The analysis involves a combination of descriptive statistics, relationship analysis via Gephi software, and a customised text mining technique (pre-processing, frequency analysis, and clustering). The cities, with populations ranging from 11,148 to 15,000,000 and predominantly located in Europe, reveal a landscape of collaboration efforts that is somewhat proportional to the city size. Citizens and national governments are the principal stakeholders (83 %) with higher governance levels primarily involved in policy and regulation formulation as well as financial support. Over 70 % of cities engage academia, research institutions, and the private sector as key stakeholders, primarily in research and innovation activities. Furthermore, 72.6 % of cities participate actively in inter-city collaborations or are members of relevant networks. Contrastingly, utilities, energy communities, financial institutions, vulnerable groups, and trade unions exhibit suboptimal integration, engaged by less than half of the cities. Optimising collaboration for urban climate neutrality necessitates an enhanced integration of diverse stakeholders, particularly those proximal to marginalised groups, mass mobilisation to leverage the synergistic potential of inter-sectoral and inter-city collaborations, and a transition from predominantly educational initiatives to more comprehensive, participatory engagement practices.

Many cities are developing plans and strategies to achieve net-zero emissions and combat climate change. However, the operational value of residual emissions remains unknown, thus challenging the integrity, transparency and impact of such pledges.

The state of the art in urban heat mitigation and adaptation is analyzed along four elements: (1) technologies, techniques, and benefits of combinatorial approaches; (2) risks and vulnerabilities assessment to incorporate the human dimension; (3) types of monitoring approaches; and (4) urban heat modeling and mitigation/adaptation scenario-making for evidence-based actions, policies, and coping strategies. Knowledge and recent advancements related to urban green infrastructure and urban materials are analyzed in detail. Lastly, we focus on how cities are advancing in heat mitigation and adaptation within the frameworks of two major initiatives devoted to cities and climate action: the Global Covenant of Mayors and the 100 Climate-Neutral and Smart Cities Mission. Key take-home messages are enucleated that link the technological and human domains both from the science and the policy-making perspectives.

The EU Mission on Climate Neutral and Smart Cities is an ambitious initiative aiming to involve a wide range of stakeholders and deliver 100 climate-neutral and smart cities by 2030. We analysed the information submitted in the expressions of interest by 362 candidate cities. The majority of the cities’ strategies for climate neutrality include urban transport as a main sector and combine the introduction of new technologies with the promotion of public transport and active mobility. We combined the information from the EU Mission candidate cities with data from the CORDIS and TRIMIS databases, and applied a clustering algorithm to measure proximity to foci of H2020 funding. Our results suggest that preparedness for the EU Mission is correlated with research and innovation activities on transport and mobility. Horizon 2020 activities specific to transport and mobility significantly increased the likelihood of a city to be a candidate. Among the various transport technology research pathways, smart mobility appears to have a major role in the development of solutions for climate neutrality.

Mitigating urban overheating is vital to create livable urban futures. Research on urban heat mitigation is plentiful, while knowledge about the actual measures local governments are implementing is limited. This study examines 7,500+ heat mitigation actions by 2,500+ cities under two flagship programs of the European Commission. The analysis reveals that cities’ strategies pivot around green- and water-based technologies (66% of the actions) while mildly leveraging permeable and reflective surfaces (35%) and rarely solar shading and wind control (8%) or stimuli-responsive/smart systems (2%). Hundreds of cities that (1) indicate extreme heat as a hazard of growing intensity and/or frequency, (2) are located in hot-summer climatic zones, (3) will experience increasingly frequent heatwaves, and/or (4) host a numerous population are not reporting any urban heat precaution. Moreover, cities show limited familiarity with combinatorial approaches and little attention to specific vulnerable population groups. Prevention, awareness, and social justice should receive more attention.

The urgency of meeting climate targets, increasing land use competition and falling solar photovoltaic (PV) energy costs have created unprecedented opportunities for innovative deployment options. This study uses geospatial data processing to quantify the potential for large-scale deployment of vertical solar panels along Europe's major roads and railways. Factors such as geography, environmental constraints, land use limitations, and techno-economic parameters, were carefully considered. An economic assessment is provided to take account of the costs and benefits and technical feasibility of the proposed PV system as compared to the fossil-fuel based transport. The findings reveal a potential PV capacity of 403 GWp within the European Union (EU). This is the equivalent to 55% of the EU's total solar PV capacity target set for 2030. Using bifacial PV modules, these systems could generate 391 TWh (terawatt hours) of clean electricity annually. Considering only railway lines, the total annual PV electricity output could potentially reach 250% of the current annual electricity consumption of the EU railway network. Additionally, the electricity generated from PV installations alongside roads would not only be cost-effective in electricity markets but also serve as a viable alternative to fossil fuels in transportation. Tapping solar PV energy along transport infrastructure can therefore significantly contribute to the EU's energy transition.

Effectively addressing climate change in line with the Paris Agreement and the EU Climate Law requires the establishment of governance structures with the participation and coordination of all levels of government and where the local level plays a key role. This is evident with the emergence of city-to-city networks of urban policymakers and supporting initiatives such as the EU 100 Climate-Neutral and Smart Cities Mission. The purpose of this article is to demonstrate how approximately 400 European cities are shaping their governance structures to tackle the complexities of achieving climate neutrality, highlighting the key elements on which cities focus their efforts. This study analyses data collected through the Expression of Interest survey of the European Commission's 100 Climate-Neutral and Smart Cities Mission, which contains inputs directly provided by local authorities responsible for implementing climate policies. The results reveal the significant progress cities have made in adapting their governance approaches to effectively address climate challenges through for instance the institutionalisation of climate change, and the introduction of enabling and participative forms of governing with the involvement of key stakeholders in the decision-making processes. It also highlights the challenges cities face concerning climate financing and the need to unlock private investments.

Cities represent unique spaces for climate mitigation where wide-ranging action to reduce emissions meets ambition and collaboration. This research work distils climate neutrality narratives for 362 cities that expressed interest in the European Mission on 100 Climate-Neutral and Smart Cities and focuses on the 112 cities selected to spearhead the process of reaching climate neutrality by 2030 (representing a mitigation potential of 318.3 megatonnes of carbon dioxide equivalent emissions). The method involves steps that profile the characteristics of these cities, enunciate cross-cutting patterns in cities’ visions by thematic groupings, and compare 14 contextual factors with 77 possible main barriers. There are both similarities and differences among the results as a basis for learning together and certain barriers can be relatively more dominant in some thematic groupings, such as fragmentation of responsibilities. As a synthesis of the main findings, the original analyses are used to derive and prioritise nine high-level recommendations based on the cities' visions, contextual factors, and expected main barriers. Opportunities for mobilising transformative change relate to transforming siloed into integrated approaches, inclusive climate governance and collaborations, innovative financing, welfare and just transition as well as planning, implementation, and policy coherence. The advances provide pioneering steps for stimulating co-learning processes among Mission Cities and beyond to support the transition to climate neutrality and open up opportunities to progress together in climate action while producing impact with global reach.

To mitigate climate change while catering to the needs of a growing population, cities need to find smarter ways to manage their resources, while reducing their greenhouse gas emissions. Since waste management and circular economy will be instrumental in this endeavour, the current level of circularity in cities, the environmental impact of related activities and sharable best practices need to be explored. This paper examines the roadmap to zero emissions of the 362 cities that expressed interest in the Horizon Europe 100 Climate-Neutral and Smart Cities Mission. Based on an unprecedented suite of city inputs, this study answers a set of research questions so far unaddressed due to the lack of a suitable dataset. The analysis focusses on a) current actions undertaken by cities in achieving a circular economy and reducing/optimising waste streams, b) envisioned circular actions in supporting climate neutrality by 2030, and c) urban sectors and metabolic flows for which circularity has a particularly high potential to mitigate climate change. Best practices are captured to create an informative set of actions aimed at policy-makers and at encouraging peer-to-peer learning. Finally, the barriers to incrementing circular approaches that emerge from the cities' self-assessments are compared to those identified in existing scientific literature to provide input for a more comprehensive conceptual framework. Overall, this study distils how circular economy imaginaries are translated into local governance and policy-making by focussing on a large group of cities. This is key to truly understand why some initiatives fail and others succeed and can inform all relevant stakeholders on the next steps to take.

Photovoltaics (PVs) provide clean and affordable energy contributing to the decarbonisation of the energy sector. High surface temperature of the PV modules reduces their efficiency and the corresponding energy production and increases the sensible heat released to the atmosphere contributing to urban overheating. For roof mounted PVs, increase of the roof albedo helps to decrease the surrounding ambient temperature, raises the efficiency of the PVs and increases the reflected solar radiation received by the modules. Numerous studies have assessed the impact of increased roof albedo on the energy yield of the monofacial and bifacial PVs for given installation characteristics and specific climatic conditions. There is a serious need to collect, analyse, compare, and parameterize the existing information in order to provide more global and holistic knowledge to the PVs industry. We have analysed 13 and 57 case studies reporting the impact of modified roof albedo on the energy yield of monofacial and bifacial PV modules, respectively. It is concluded that, on average, increasing the roof albedo by 0.1 contributes to enhance the energy production of monofacial and bifacial PV modules by 0.7% and 4.55% respectively while delivering important co-benefits to urban heat mitigation. Parametric relations between the potential increase of the roof albedo and the increase of the annual energy yield are proposed for both monofacial and bifacial PV modules. The impact of the geographic and installation parameters on the energy production of the modules is analysed and discussed. The results of such a study could help to identify the optimal roof albedo for maximizing energy performance and reducing energy costs.

Cities are increasingly becoming critical climate actors. However, their preparedness and ambition in forging climate-neutral futures is hard to ascertain. In this study, we analyse the Expressions of Interest in the Mission on 100 Climate-Neutral and Smart Cities by 2030, an unprecedented dataset of city inputs to 374 different questions on the transition to (net) zero. We i) delineate emissions baselines, accounting methodologies, and inventories' completeness (sectors/sources, carriers, gases), ii) analyse emission trends and cities' capacity to deliver on their climate mitigation commitments, iii) examine the estimated magnitude and origin of residual emissions by 2030 together with the envisioned offsetting strategies, and iv) elucidate gaps, methodological deficiencies, and forms of assistance. Data suggest that if all 362 eligible cities were to reach climate neutrality, approximately 650 MtCO2eq would be removed. However, this would require at least a quadruple effort in half the time compared to current mitigation achievements. Beyond the challenge of emissions baselining, cities lack adequate data collection and monitoring systems and show little familiarity with non-technological and technological avenues to tackle harder-to-eradicate emissions. Capacity building will be key across multiple (e.g., technical, financial, operational) domains to turn ambitious mayoral commitments into factual contributions to climate mitigation.

Renewable energy sources have emerged globally as a key lever to ensure energy security and to promote climate mitigation. Cities need to exploit this energy transition, but how they are building their strategies and actions is undetermined. A new dataset, collected through the European 100 Climate-Neutral and Smart Cities Mission, offers unique insights on the 362 cities which expressed the ambition to reach climate neutrality by 2030. Insights include their level of preparedness, ambition, capacity and the risks envisaged in the pursuit of zero-emission and greener futures. This study focuses in particular on the role of renewable energy across high greenhouse gas emitting sectors in cities (e.g. buildings, mobility, waste and industry). It analyses i) the status quo for renewable energy generation, consumption, and policymaking, ii) the key measures to enhance and upscale renewable energy deployment in the near future, and iii) how policies and relevant instruments will evolve to curb emissions and accelerate the energy transition. The insights that emerge from the analysis are discussed in relation to existing evidence, to inform future research strands and forms of assistance for cities. Overall, for cities to deliver on large renewable projects, efforts need to be intensified, barriers need to be lifted and multi-governance approaches must be operationalised.

Owing to the synergic effect of heat island and global warming, urban overheating has become a growing concern. Solutions to mitigate the thermal stress and provide enhanced comfort conditions are numerous, yet not equally investigated. A rather underexplored avenue is that of evaporative cooling systems based on water misting. The cooling effect is substantial and highly localized, so that this technology lends itself to integration in smallscale urban cooling shelters. This paper explores the potential of such solution, through an experimental campaign in which the misting system works in combination with other technologies, such as sun and wind protections, as well as smart and renewable energy management. The monitoring was carried out in the ENEA Casaccia research center (Rome, Italy) in the summers of 2021 and 2022. Eight different test configurations were evaluated to determine the performance of the system. It was found that the most effective configuration includes a windshield protection with maximum reduction of the perceived temperature of 10 degrees C. The analysis further reveals that the use of larger nozzles' spacing (130 cm vs. 100 cm) slightly worsens the performance of the system (by around 1 degrees C). Conversely, switching from continuous, manual control to a comfort-based control logic for the pump activation comes with similar comfort performance but drastically reduced water and electricity consumption.

Urban overheating is the most documented phenomenon of climate change impacting humans. This article presents the most recent developments on the magnitude and characteristics of urban overheating and the potential synergies with global climatic change. It analyses the latest qualitative and quantitative data on the impact of higher urban temperatures on buildings’ energy supply and demand, heat-related mortality, morbidity and wellbeing, human productivity, survivability of low-income populations, and environmental quality of cities. It describes the state of the art on the development of innovative mitigation materials, advanced urban greenery, heat dissipation, and evaporative techniques as the main mitigation and adaptation technologies to offset the impact of urban overheating. It also analyses the current knowledge on the impact of each mitigation technology on energy, health, environmental quality, urban economy, and survivability. Finally, this article presents the main future challenges related to urban overheating and proposes a specific research agenda to alleviate and counterbalance its impact on human life.