Towards a Science of Scaling for Urban Climate Action and Governance

Abstract The scaling of urban climate action and its governance is rapidly becoming a central focus in the urban climate governance literature and policy debates. Building on the broader scaling literature and inspired by related initiatives in other fields, this article calls for the development of a systematic “science of scaling” for urban climate governance. Such a science of scaling may help to give a better understanding of how well-performing urban climate action and its governance can be multiplied, accelerated and broadened (ie horizontal and vertical scaling and scaling out, up and down), and it may help to uncover scaling trajectories towards systemic change in cities (ie deep scaling).


I. Introduction
For a long time, cities, city regions, urban communities and other large human settlements (referred to here as "cities") have been lauded for taking climate action where nation states were seen to fail. 1 They have received praise for rapidly embracing new technologies and pursuing behavioural changes to reduce urban resource consumption and waste production. 2 Cities have also received accolades for experimenting with novel forms of urban climate action and its governance and for the dissemination of lessons from these experiments through city-to-city networks and other platforms. 3Finally, high hopes have been expressed regarding the potential to scale these urban climate actions and their governance (locally, regionally, nationally and even globally) and to make a significant contribution to keeping global warming under 1.5°C. 4owever, this narrative is rapidly shifting.Increasingly, scholars are pointing out that what we know about the scaling of urban climate action and its governance does not paint a hopeful picture.In this context, scaling is understood as: (1) the increased use of innovative forms of urban climate action and its governance beyond the individuals and collectives involved in their initial development and implementation; (2) transformative and systemic change achieved through innovative forms of urban climate action and its governance; or (3) a combination of both (1) and (2). 5 Scholars point out that innovative urban climate action and its governance are not resulting in fundamental changes across institutional levels 6 ; that there is no buy-in from the global majority of cities and urban citizens to take action locally (through direct replication or adjustment to the local context of innovations from elsewhere) 7 ; and that, at best, technological innovations have scaled but behavioural and institutional ones have not scaled so much. 8n sum, over recent years, scholars have begun to point out that, whilst the scaling of (innovations in) urban climate action and its governance is essential, it is not yet happening to the extent that it makes a significant contribution to keeping global warming under 1.5°C. 9Related observations are made in policy debates and documents.For example, the recent European Green Deal is explicit regarding the need for large-scale changes and the difficulty of achieving these changes under a business-as-usual scenario in areas such as building retrofits and smart urban transport.The European Commission lauds what has been achieved in a piecemeal manner over recent decades in terms of, among other things, reductions in city-related greenhouse gas emissions, but it stresses that deep, mutually reinforcing transformations are required to achieve the European Union's climate ambitions. 10or these reasons, scholars of urban climate governance have begun to focus on scaling as a topic for scholarly inquiry in and of itself if we wish to know how the scaling of urban climate action and its governance can best be achieved. 11This article seeks to contribute to this rapidly emerging debate on the scaling of (innovations in) urban climate action and (innovations in) its governance.It does so by mapping, exploring and interrogating the scaling debate in the urban climate governance literature, and it delves into discussions on scaling in other policy areas to enrich this debate.This article builds on a narrative review of the literature on scaling urban climate action and governance.For the review, peer-reviewed journal articles were sourced from the Web of Science and Google Scholar databases using "urban AND scale AND climate AND (action OR govern*)" as keywords.In addition, the same databases were searched for the keywords "science of scaling" to identify broader debates on this topic. 12he aim of this article is to begin working towards a systematic "science of scaling" for urban climate governance, which seems necessary if we wish to increase the likelihood that urban climate action and its governance will achieve systemic change. 13In what follows, following the broader scaling literature, some essential elements of such a science of scaling for urban climate governance are presented.But first, it is explained why a science of scaling has become so essential for this area of scholarship at the beginning of the 2020s and how, and with what results, insights from the scaling literature have been applied in this area to date.

II. How the scaling challenge has entered urban climate action and governance scholarship
For a long time, the development, use, maintenance and transformation of cities have been governed through laws and regulations introduced by national, regional and local governments. 14Whilst such laws and regulations have served cities well in the past,15 they face challenges in dealing with the urgently required climate change transformation of cities (mitigation and adaptation).The problems include, but are not limited to: a lag between the development of law and regulation and the growth of cities in low-and middle-income countries 16 ; the slow replacement rate of existing buildings and infrastructure in cities in developed economies17 ; and the difficulty of changing or altering the existing property rights of the owners, users and other beneficiaries of buildings, infrastructure and landmeaning that new urban law and regulation often exempt from compliance existing buildings, infrastructure and land use in cities. 18 Facing these challenges, governments have developed alternatives for law and regulation (sometimes in collaboration with non-governmental parties) to initiate urban climate action. 19For example, in 2010, the City of Amsterdam introduced a Climate and Energy Fund.The Fund makes finance available for projects that, among other things, help to reduce the city's carbon emissions but that cannot find funding elsewhere.The Fund operates as a revolving loan fund, meaning that once a loan is paid back to it the funds are made available again to other projects.The Fund helps the City of Amsterdam to reduce the city's carbon emissions and to normalise the development of low-and even zero-carbon construction projects. 20imilarly, these challenges have spurred non-governmental parties to take voluntary urban climate action and to develop and implement strategies to govern this voluntary action.For example, around the globe, for-profits and not-for-profits have introduced building rating and certification programmes, with a dominant example in Europe being the Building Research Establishment Environmental Assessment Method (BREEAM). 21hese programmes allow the environmental impacts of existing and new buildings to be evaluated.Depending on its performance, a building will be given a higher or lower rating, typically represented by a certificate, to help (future) owners or tenants to distinguish between poor-performing and well-performing buildings.It is then expected that owners and tenants will increasingly call for buildings with a low environmental impact and that developers will begin building these.
Another response is represented by a mushrooming of city-to-city, city-to-citizen and city-to-firm climate networks.In such networks, cities can cooperate and share information on how to take and govern climate action (eg there are well-known municipal climate networks such as the Covenant of Mayors for Climate and Energy, which was launched in Europe in 2008); they can collaborate with citizens and firms within the same jurisdiction (an example here is the Transition Town Network); and they can even embrace the private-sector and non-governmental initiatives that provide "off-the-shelf" urban climate action (an example being the Rockefeller Foundation's 100 Resilient Cities programme, which has merged into the Resilient Cities Network). 22

Unpacking and understanding the scaling challenge
The developments discussed should be understood within the context of at least three decades of exceptionally active debates about the role of cities in the global response to climate change.At the beginning, during the 1990s, cities were increasingly seen as the most promising level for governing climate action. 23Arguably, Local Agenda 21, adopted at the Earth Summit in Rio de Janeiro in 1992, was a landmark and paradigmshifting publication that recognises and explicitly mentions cities as important sites for climate action. 24Local Agenda 21 gave (local) governments and policymakers legitimacy to put climate mitigation (and later adaptation) on the urban agenda, and it provided an impetus for academics to begin systematic and ongoing inquiries into the how, what, why and where of urban climate action and its governance. 25rom the early 2000s onwards, the narrative of cities, climate change and urban climate action and its governance has grown rapidly.In a first storyline, cities are seen as one of the main victims of climate change.It is commonplace to acknowledge that the negative results of climate change will hit cities hardest because of their high population densities, their role in the global economy and function as capital sinks and their often-vulnerable locations. 26A second storyline takes a different point of view and looks at cities as key sources of climate change.More than half of the world's population lives in cities (and that number will only rise), and most global carbon emissions and resource consumption can be attributed to urban lifestyles, whilst cities make up less than 5% of Earth's land surface. 27A third storyline sees cities as sites of opportunity because their population densities and relative affluence mean that major reductions in energy, finite material use and greenhouse gas emissions could be realised relatively quickly in them. 28uring the 2010s, the narrative grew thicker.In a fourth storyline, cities are lauded as saviours of the planet in the face of climate change. 29Cities are reported to be rapidly embracing new technologies and behavioural changes to reduce city-related greenhouse gas emissions and to change urban lifestyles (in part by embracing alternatives to traditional, government-led direct regulationas discussed previously). 30Cities are also found to collaborate actively with citizens and businesses to develop tailored urban governance climate interventions and to operate in regional, national and international city networks, helping to build knowledge regarding urban climate action, disseminate best practice and, in international forums, raise the voice of cities as meaningful players in global climate governance (again, these tailored interventions are developed as alternatives to traditional, government-led direct regulationas discussed previously). 31This role of cities was, for example, underlined in 2015 in the lead-up to the signing of the Paris Agreement, in the New Urban Agenda in 2016 and in the European Union Strategy on Adaptation to Climate Change in 2021. 32owever, in the early 2020s, the narrative has now begun to shift. 33Increasingly, scholars are stressing that cities are not taking the necessary actions and making changes of the magnitude and at the speed required to keep global warming to 1.5°C. 34Their work hints at different challenges.Cities may have embraced new technologies, innovative forms of behavioural change and governance alternatives in too haphazard a way, and they may now be struggling to merge these into a coherent whole that is larger than the sum of its parts. 35Some cities have managed to harvest the "low-hanging fruit" by such actions as increasing the building energy efficiency of new buildings, but they may have been less successful in tackling more complex problems such as energy retrofits of existing buildings, 36 whereas other cities may have found it difficult (or perhaps have been unwilling) to learn from and repeat each other's best practices. 37Replicating best practices is often challenging because their performance and impact are strongly affected by local contexts and local actors. 38As a result, the combined climate activities and governance interventions of cities have not (yet) accumulated to a point at which they trigger a fundamental change in norms, values and rules across cities globally. 39hese issues have rapidly entered the urban climate governance research agenda and point to a common denominator: a scaling challenge.We have now reached a point where we need to think critically and systematically about how to stabilise and accelerate, how to broaden and grow and how to replicate and transfer the innovations in urban climate action and governance that have mushroomed around the world for more than three decades. 40Equally importantly, we have reached a point where we need to think critically about how to achieve the systemic changes that are critical to the rapid transformation of our cities in a way that helps to keep global warming to 1.5°C. 41

III. State of the art: urban climate governance scholarship embraces the scaling challenge
Increasingly, scholars of urban climate governance are embracing this scaling challenge and discussing the need for a better understanding of the scaling of urban climate action and its governance.When carrying out an overview of the literature, three different areas of focus stand out.First, scholars have begun to explore where we can expect to find scaling of urban climate action and its governance, resulting in a range of ideal types of scaling.Second, they have begun to explore the conditions that may contribute to or hamper this scaling, resulting in a broad set of (expected) drivers of and causal mechanisms for scaling.Third and finally, scholars have introduced different ways of looking at scaling by mapping, exploring and interrogating the urban climate actions that can be scaled (the "what" of scaling), the urban climate governance and other mechanisms required for such scaling (the "how" of scaling) and the interplay of these elements and other dynamics that make scaling processes context-specific or more generally applicable (the "replicability" of scaling).

Types of scaling
The area of focus that has received most attention is where scaling of urban climate action and its governance may be expected and what forms it may take.Despite some minor quibbles over terminology, 42 scholars largely agree on three ideal types of scaling.Of course, the boundaries of these types will not be as easy to define in real-world settings as they are when discussed in the literature, and there are likely to be interactions and interdependencies between the types. 43he first type of scaling is characterised by the multiplication (in time, space or both) of urban climate actions and their governance and parts thereof, the replication of (conceptually) similar actions and governance interventions to (conceptually) dissimilar contexts and the replication of the principles of actions and interventions to (conceptually) similar contexts. 44The conventional terminology used for this ideal type is "horizontal scaling" and "scaling out". 45This type of scaling is typically expected to occur voluntarily on the basis of learning and the exchange of experiences and knowledge. 46For example, the BREEAM building certification programme (discussed earlier) was originally launched in the UK and has been replicated with local adaptations in countries such as Austria, Spain and Sweden. 47Similarly, the principles of the Transition Town movement have been replicated in many European cities, leading to a variety of local actionsfrom urban agriculture in Essen, Germany, to a community centre that raises awareness about environmental and social sustainability in Linda-A-Velha, Portugal. 48he second type of scaling is characterised by the transferring and spreading of urban climate actions and their governance and parts thereof through administrative or organisational levels other than the levels at which they originated.This type of scaling is seen as particularly promising in multi-level systems such as the European Union, where promising local initiatives (such as efficiency standards for buildings) can be made mandatory in a large geographical region. 49It is likely that the conditions for such scalingsuch as changes to laws, policies or institutionswill have to be created intentionally. 50For example, an action or governance intervention may be integrated at a higher system or governance level (from local to national, from national to global or even from local to global) and, once integrated, the responsibility or accountability for it can be further redirected 51 including to lower system or governance levels. 52The conventional terminology used for this ideal type is "vertical scaling" and "scaling up".This type of scaling is typically expected to require some form of power 53 whether this is a voluntary and self-organised pull mechanism or a forced and authoritarian push mechanism. 54For example, in 2021, twenty Danish municipalities across five regions adopted development plans to reduce their greenhouse gas emissions by 2030 by up to 70% relative to 1990 levels and to become carbon neutral by 2050. 55This is a direct implementation of the voluntary standards for urban climate planning that were developed by the C40 city-to-city climate network. 56he third type of scaling is concerned with systemic change rather than the directional multiplication, replication, transferring or spreading of urban climate actions and their governance (that is, horizontal or vertical scaling and scaling out, up and down). 57Put differently, this type of scaling has a focus on improvement at scale rather than implementation at scale. 58The conventional terminology used for this ideal type of scaling is "deep scaling". 59It is conceptualised as a process of social transformation that occurs "when sustainable values and norms become culturally and institutionally embedded by individuals and institutions". 60It seems unlikely that deep scaling is a process that can be planned in a linear manner; rather, it requires multiple strategic interventions in different social, economic, political and cultural contexts. 61The latter is indeed a point of departure in the transitions literature and is central to the multi-level perspective (MLP) that acknowledges that the scaling up and scaling out of innovative climate actions (innovations at the "niche" level in MLP jargon) could ultimately result in systemic change (change at the "regime" and "landscape" levels in that same jargon). 62 Drivers and causal mechanisms of scaling Considerably less attention is given in the literature to the conditions that contribute to or hamper the scaling of urban climate action and its governance.Identifying these conditions requires analytical scrutiny of real-world instances of such cases, but scaling is notoriously difficult to study empirically because of the long timespan that is often needed for something to scale and the many moving parts involved.63 That being said, and as illustrated by the ideal types, the urban climate governance literature (obviously) touches on coercion and cooperation as important factors for the scaling of urban climate action and its governance.Coerced scaling involves, among other things, the changing of laws and regulations to scale urban climate action and its governance, 64 and cooperative scaling involves, among other things, the changing of institutions and power relationships to scale climate action and its governance, but without the force of law.65 Other broad conditions that drive scaling or otherwise affect it can be summed up under the headings of finance (ie the profitability of urban climate action for developers and end-users), confidence in the solution (ie the reliability of the technical, environmental and economic performance of urban climate action), complexity (ie the financial, human, information and technical resources required for developers and end-users), compatibility (ie the technical, geographical, cultural and normative alignment of urban climate action) and information (ie the communication between the instigators of urban climate action and its developers and end-users).66 Besides a focus on these institutional, structural and contextual conditions, there is an ongoing (niche) debate in the urban climate governance literature on the (assumed) role that frontrunners (also termed "leaders", "innovators", "pioneers", "trend-seekers" and "explorers") play in the process of scaling urban climate action and its governance.67 This debate echoes a process of linear scaling described in the diffusion of innovations literature: urban climate action or its governance begins small with innovators, is then taken up by early adopters and via them makes the jump to the majority and laggards.68 Typically, large and affluent cities in the Global North are seen (and studied) as the innovators and early adopters in this debate, and the assumption is quite easily made that once these cities are on board cities elsewhere will follow.69 It remains to be seen, however, whether frontrunners play as strong a role in the process of scaling of urban climate action and its governance as is often assumed.In nonhomogeneous environments (with large variety in those that make up the majority) such as the global pool of cities, city regions and urban communities (and, perhaps more importantly, the people that live, work and invest in them), there is a substantial risk that the majority (and laggards) are not convinced by the experiences and insights of the frontrunners because they do not consider them as their peers or equals 70 a challenge that has indeed been flagged in the urban climate governance literature.71 3. Different ways of looking at scaling Over the years, scholars have both embraced existing heuristics and analytical frameworks and developed novel ones that help to capture the scaling of urban climate action and urban climate governance.72 For example, the diffusion of innovations framework presents a rather straightforward view on scaling: an innovation begins small and, if it scales, it does so by going through different phases of ever-larger adoption.To use the terminology introduced above, this first involves a scaling out of the innovation within a group of innovators before there is a scaling up to the group of early adopters.Once the innovation has scaled out far enough within that group of early adopters, it is expected to scale up again to the majority, and so on until it has become transformative.73 A different way of looking at scaling of urban climate action and its governance is the small-wins perspective.74 Rooted in organisational psychology, 75 this holds that transformative change may result from the accumulation of small wins and occurs in a non-linear manner (contrary to the linear view taken by the diffusion of innovations perspective).To this end, targeted governance interventions are required to introduce a variety of propelling mechanisms that accelerate the application of innovations (the small wins) but within a larger vision of transformation.The central idea of this perspective is to "[stimulate] distributed innovation efforts to foster gradual, yet in-depth change in a desired direction".76 The small-wins perspective calls for a shift away from seeking large-scale transformation through bold policy programmes (which may be too overwhelming for policymakers, practitioners and citizens) towards modest policy planning that cultivates small wins and governs them towards the desired outcome.77 Yet other ways of looking at scaling are provided in sustainability transition studies, 78 an area of scholarship concerned with "large-scale disruptive changes in societal systems that emerge over a long period of decades". 79Among other things, sustainability transition studies are concerned with the mechanisms and driving forces that can accelerate the uptake of innovations and lead to urban climate transitions, such as contestation, competition and cooperation.80 Acceleration is seen as an important phase of transitions in which innovations have scaled and are beginning to combine, and in doing so they cause regime change by affecting policy, business and consumer practices.81 A central overlap with the small-wins perspective is the expectation that it is likely that large-scale change of technological systems, ecological systems and institutions will be a non-linear process; the major difference is that the focus of transition studies is on "radical, systemic, and accelerated change" (contrary to the incremental view taken by the small-wins perspective).82 IV.Looking forward: a science of scaling for urban climate governance scholarship Scaling is rapidly becoming a central focus in urban climate governance scholarship, and the time seems ripe to pursue a science of scaling for urban climate governancean endeavour that is also being undertaken in related academic and policy areas.83 The overall aim of a science of scaling is "to contribute to building a culture of critical thinking on [scaling]" 84 and to increase the likelihood that (innovative) urban climate action and (innovations in) its governance will benefit society and make a meaningful contribution to keeping global warming to 1.5°C.Such a science of scaling should be systematic, and it essentially pursues four objectives.85 A first (obvious) objective of a science of scaling for urban climate governance is to answer ontological questions.86 To take the extreme positivist and interpretivist positions: does the scaling of urban climate action and its governance exist as an objective, predictable phenomenon (ie a mechanism or process that will emerge once the "right" conditions are in place) or does such scaling only exist by virtue of its context and the subjects involved (which include the scholars who study scaling)? Cosidering the abovementioned typologies, conditions and perspectives, it is likely that the answer will lie somewhere between those extremes.Nevertheless, in order to understand whether and to what extent the scaling of urban climate action and its governance can be designed and nurtured, and thus governed and managed, answering such questions is essential.
A second objective is to answer epistemological questions.In other words, how can we know that the scaling of urban climate action and its governance exists (be that as an objective phenomenon, a subjective one or something in-between)?This calls for careful thinking about the methods and tools required to study such scaling. 87Given the long timeframes and interdependencies between the many conditions involved in scaling, it is likely that careful case studies of a process-tracing type are required first in order to grasp the broad boundary conditions and mechanisms that recur across real-world observations of scaling. 88From there, configurational comparative research may help us to uncover evidence-based scaling pathways that are broad enough to guide future urban climate action experiments (including innovative urban climate governance interventions) but are not oversimplified to the point where they are little more than the broad ideal types introduced earlier. 89 third objective is theory building and testing.Practically, this calls for a move away from studying "best practices" and "innovations" in urban climate action (including its governance) and their stabilisation, embedding, speeding up, growth, replication, transfer and so on to questioning and refining scaling pathways and trajectories.Ideally, such theorybuilding and testing will be undertaken with the ambition of informing real-world governance and policy initiatives that seek large-scale transformational change.Obviously, scholarship needs to cast a wider net beyond the typical "leading" cities and initiatives in the Global North and increasingly include cities and initiatives from the Global South as well as cities and initiatives from the Global North that currently operate in the shadow of the leaders.
A fourth objective is to reflect on the practical application of the existing knowledge of scaling and the different ways of looking at it.Is the work produced by the academic community of value to policymakers and practitioners?Does this work help them, ultimately, to implement policies and undertake urban climate action that help in keeping global warming to 1.5°C?It is likely that this will require closer collaboration between the academic, policy and practitioner communities to ensure that our academic work will have practical value.It may also ask for introspection by the academic community to understand whether and how decades of our collective work in this area have (or have not) contributed to the required scaling of urban climate action and its governance.

V. Conclusion: why a science of scaling for urban climate action and governance is essential
Scaling of urban climate action and its governance is rapidly becoming a central focus in the urban climate governance literature and policy debates.Building on the broader scaling literature, this article has called for the development of a systematic science of scaling for urban climate action and governance.Such a science of scaling is relevant not only to gaining a better understanding of the ideal types of scaling (such as scaling up and out and deep scaling) but also to producing practical and applicable lessons to aid governance and policy initiatives that seek large-scale transformational change.For example, for the European Green Deal to be successful, it seems that it will be essential to gain an understanding of how its various parts (such as the New European Bauhaus 90 and 100 Climateneutral Cities by 2030 91 ) can be designed and implemented to achieve, in cohorts, the large-scale transformation for which the European Commission is aiming.
The call for a science of scaling made in this article is inspired by similar calls and advances made by scholars who study scaling in other policy areas.Put simply, a science of scaling for urban climate action and its governance aims to understand the essence of scaling.It questions whether scaling is something that can be designed and nurtured, and thus can be governed and managed, or whether it is something that emerges in a nonpredictable mannerand it could question whether scaling is as desirable as is often claimed in the urban climate literature.Its ambition is to increase the likelihood that (innovations in) urban climate action and (innovations in) its governance will benefit society. 92As Newell, Daley and Twena have recently illustrated, thinking systematically about scaling can break new ground for theory and practicethey suggest, among other things, the exploration of the dynamics that allow "shallow" forms of scaling (scaling up and out) to evolve into more transformational change over time (deep scaling). 93qually importantly, by committing to (the development of) a systematic science of scaling for urban climate action and its governance, this area of research may avoid some of the challenges and pitfalls experienced by scholars who study scaling in related areas.These include, but are not limited to, a bias towards studying success stories of scaling (and not failure stories), 94 a bias towards conceptualising scaling as a linear process (rather than a dynamic, multiplicative or exponential one) 95 or a bias towards conceptualising scaling as a maximising (rather than a sufficing) process. 96In short, a science of scaling may prevent us from ignoring the important trade-offs that are likely to be required when it comes to scaling urban climate action and its governance. 97As this article has indicated, urban climate scholarship does not have to start from scratch in the development of a science of scaling.The building blocks are available in related areas of research and in the broad urban climate scholarship itself.