Les dossiers 

In recent years, a growing number of cities and other sub-national authorities have adopted net-zero targets as a cornerstone of their climate policies. By 2023, 252 cities with more than 500,000 inhabitants had committed to achieving carbon neutrality by 2050 at the latest, representing 800 million people1. More broadly, there has been a sustained increase in net-zero pledges from states (149) and non-state actors led by listed companies (929). The concept of “net-zero emissions” (or "climate neutrality") refers to a desired state in which residual anthropogenic greenhouse gas (GHG) emissions, if any, are offset by equivalent carbon removals from the atmosphere. Echoing the scientific urge to achieve global climate neutrality by mid-century2, net-zero targets quickly became an “article of faith” as well as an “accounting goal” at multiple organisational levels3. In 2015, the Paris Agreement set climate neutrality as a political horizon for governmental climate policies, while also mainstreaming it for non-state actors. The financial sector, businesses, regions and cities were invited to take increasing responsibility in implementing these transformative changes towards a zero-carbon world.

The scientific concept of net-zero has had to go through a process of translation to be integrated into organisational decision-making, governance and reporting, which has encouraged the development of specific management accounting systems4 and tools in different organisations. While net-zero accounting tools are key assets in moving towards climate neutrality beyond mere policy statements, they are rather novel socio-technical innovations. They still lack implementation and standardisation and rely heavily on questionable hypotheses that are often overlooked. To name but a few, the definition of “matters of concern”5, spatial and temporal framing and uncertainties – for instance the geographical scope, measurement challenges – such as choosing a metric, responsibility and effort allocation – that is deciding on who is to implement mitigation levers, as well as embedded policy choices and socio-cultural effects in practice, are all left unpacked. More generally, this “black boxing” of ecological issues into accounting methods and tools raises multiple scientific, technical, socio-economic, political and organisational questions about how these crucial targets and related instruments are designed, implemented and used by cities and regions aiming at climate neutrality.

More recently, a second generation of such “net-zero policies” is addressing new environmental issues, namely biodiversity and soil conservation. While No Net loss of biodiversity is not new and has been discussed by conservationists for decades6, No Net Land Take has recently been introduced into French law. The French Climate and Resilience Law7 proposes to halve land take by 2031 and achieve No Net Land Take by 20508, thus creating a major environmental policy goal and a transformative planning tool. Regions and cities will be responsible for allocation and will be held accountable to this target. In line with Net Zero Emission, the No Net Land Take policy involves a process - still underway - of translating complex scientific concepts (mainly land take, i.e. the expansion of settlements, industries and infrastructures at the expense of agricultural land, forests or other semi-natural or natural areas) and metrics (in France, the area of land that goes from non-artificial to artificial) into a set of operational and standardised methods and tools to be adopted by local authorities. Some of the challenges raised by these emerging “net-zero accounting” tools for land take are like those raised in the case of climate, while others are specific to soils.

Furthermore, cities are key actors in the achievement of national environmental transition goals. First, they are home to the majority of the world's population and therefore to our impacts on climate, accounting for around 60% of global greenhouse gas emissions, as well as other environmental pressures such as the loss and fragmentation of natural land9. Second, local jurisdictions, embedded in territories, have many drivers for the necessary socio-economic changes.

This article examines cities’ recent efforts in this direction through the lens of ecological accounting, a field of research at the intersection of conservation ecology, ecological economics and management science10. It offers critical and analytical resources to shed light on the net-zero accounting methods and tools used by cities, and the questions and challenges raised by their development and diffusion.

• 1. Net Zero Tracker. (2023).
• 2. IPCC (2014).
• 3. Allen et al. (2022)
• 4. These systems are defined as a “set of subjective information systems whose purpose is to measure the value of an entity’s means and results” (Richard et al. 2018).
• 5. Latour (2004).
• 6. Levrel (2020).
• 7. LOI n° 2021-1104 du 22 août 2021 portant lutte contre le dérèglement climatique et renforcement de la résilience face à ses effets, 2021-1104
• 8. In French “Zéro Artificialisation Nette” or ZAN.
• 9. Ulpiani et al. (2023).
• 10. Feger & Mermet (2021).

A first set of challenges for net zero policies relates to the measurement of environmental impacts at the city scale. This includes defining and standardising specific biophysical metrics, designing budgets and trajectories, allocating responsibilities and efforts, and designing offset mechanisms.

Caronte Canal and surrounding areas from Copernicus satellite data

©Credit: European Union, contains modified Copernicus Sentinel data, 202411

The commonly accepted measure of climate impact is the CO2 equivalent (CO2e) tonne. The amount of different greenhouse gases emitted by a given entity is expressed in terms of their cumulative warming power on the climate system and compared to that of CO2. Their respective global warming potential (GWP) is  expressed over a given time period, conventionally one hundred years. While this metric might appear quite straightforward, it is subject to several structural issues: the scope or scale of emissions considered, the accuracy of estimating distributed emission sources, the list of gases considered, the time scale chosen, and the tendency of this metric to make gases the same, i.e. to make emissions from different nature, processes and activities comparable12. No such single indicator exists for land degradation. The dichotomy between hypothetical 'natural' and 'artificial' land leads to a major conceptual ambiguity that hides most threats to soil health such as the expansion or intensification of agriculture and forestry13, and delays the implementation of related policies14. Land use and land cover classifications can help assess land patterns at a global scale through digital satellite mapping, but land 'quality' in terms of soil ecosystem properties, functions or services is much more complex to assess as it depends on local land uses and values15.

Standardising metrics allows cities to take into account past and current trends, which can help them set a date for achieving neutrality. Typically ranging from 2025 (Copenhagen) to 2050 (Paris), in most cases with interim target(s), the neutrality date enables the definition of emissions trajectories and carbon emissions budgets (gross, annual, net) to be allocated to different sectors, activities and ultimately actors. The breakdown of a global budget into sectoral budgets is also a political negotiation process aimed at triggering commitments to reduce impacts. For carbon, a definition of scope is needed to address either only territorial emissions (geographical criteria) or also induced emissions, i.e. energy, transport and goods consumed (responsibility criteria). For land, private property, planning law, infrastructure, private housing and economic policies are significant constraints, raising questions of environmental justice towards disadvantaged areas, which are often located on the most polluted land but have the greatest need for housing and economic development.

A final fundamental challenge on the biophysical side is the other side of the “net”. Net-zero accounting assumes the possibility of 'positive' environmental impacts to compensate for residual negative impacts. For carbon, these offsets rely on the fact that Earth's ecosystems (such as oceans, forests and soils) have an inherent, albeit limited, capacity to capture and sequester a fraction of our anthropogenic carbon emissions. Beyond this threshold, net-zero climate policies rely on yet-to-be-developed carbon removal technologies, either by capturing direct emissions at source or by maintaining, enhancing or creating new carbon sinks. Emerging offset projects and markets, often implemented outside urban boundaries, raise the issue of land use conflicts and land grabbing, particularly in the Global South16, but also present huge uncertainties about the permanence and reversibility of sequestration (i.e., GHGs released back into the atmosphere after a period of time). In the case of No Net Land Take, notwithstanding the lack of reliable - if any - scientific standards for soil restoration, there are significant challenges regarding the technical and economic feasibility of producing functional soil on a large scale. While legislation such as the Climate and Resilience Law has yet to address these technicalities, the implementation of these compensation solutions in urban and peri-urban areas increases competition for land use and the dependence of cities on their hinterland17.      

• 11. https://browser.dataspace.copernicus.eu/?zoom=15&lat=43.39963&lng=5.032… Accessed November 2024.
• 12. MacKenzie (2009).
• 13. FAO, ITPS, GSBI, SCBD, & EC. (2020).
• 14. Marquard et al. (2020).
• 15. Cousin, Desrousseaux et Leenhardt (2024).
• 16. Ecosystem Marketplace. (2022)
• 17. Barral & Guillet (2023).

A second set of questions and challenges relates to the integration of these targets, budgets and trajectories into existing accounting systems and tools. As the forthcoming IPBES (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) report on "Methodological assessment of the impact and dependence of business and nature's contribution to people" will probably show, there is a wide variety of approaches available to meet different needs and situations. However, if these biophysical measures are to influence decision-making and effectively achieve transformative organisational change, they would need to be integrated into existing accounting information used to steer organizations. There are a number of issues that need to be considered in this regard, relating to monetisation, valuation methods and integration.

The first question concerns the monetisation of these ecological impacts. While some believe that value pluralism is essential to resist the value monism imposed by economics and ensure a liveable world for all18, others believe that biophysical indicators alone cannot challenge the economic narrative focused on financial metrics. Indicators and environmental dashboards19 are therefore opposed to green budgeting, a tool to label funds according to their negative or positive impacts, or natural capital accounting.

Second, putting a "price tag" on carbon or land is not that straightforward. Existing methods for monetising the environment fall into two categories. The first considers ecosystems as assets that provide ecosystem services to the economy and society. Hence, most valuation techniques tend to value these ecosystem assets and services based on market or net present value. Another strand of approaches focuses on estimating the cost of restoring ecosystems, defined in biophysical terms. The two methodologies are based on differentiated worldviews, on the relationship between nature and society, considering natural capital either as an 'asset' or as a 'liability', and lead to different outcomes in terms of ecological conservation. 

Thirdly, how this value is then used and integrated, or not, into the existing accounting system is crucial. Ultimately, economic rationale and metrics are the cornerstone of public action and accountability. Promoting transformative change therefore requires transforming information systems, tools and practices to integrate these new values. To do this, the paradigm of strong sustainability assumes that natural and financial capital are not interchangeable and should be maintained independently. Some cities are already experimenting with ecological accounting frameworks20. Finally, the development of ecological accounting systems and tools to guide cities towards net zero policy design, implementation and evaluation will require further articulation with management information systems built at micro and macro levels, especially in enterprises (with the European Directive on Corporate Sustainability Disclosure) and at national and global levels (like United Nations proposition of a System of Environmental Economic Accounting).

• 18. IPBES (2022).
• 19. Ekins, Milligan & Usubiaga-Liaño (2019).
• 20. As an illustration, the CARE accounting model (Comprehensive Accounting in Respect of Ecology) is currently being developed in different French local territories to work on the connection between the monitoring of ecological transitions with public accounting and finance.

In short, while the number of net-zero pledges has risen sharply in recent years, their ongoing translation into policy documents and legislation goes hand in hand with the development of management information systems and tools. Whether for climate or land use, the ability of these net-zero accounting tools and practices to effectively steer transformative change depends on how they address the political questions and challenges of this daunting task. From biophysical measurement to gradual integration into accounting systems and tools, net-zero climate and land use policies are fraught with questions. Where further legislation is needed to drive standardisation, feedback from experimentation, best practice sharing and action research are needed to ensure that cities are up to the challenge.

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Eulalie Saïsset is a PhD student in economics at Sciences Po (CRIS), CIRED and the French Ministry for Ecological Transition. She is working on the territorial planning of the no net land take target and the inequalities it implies. Eulalie holds master's degrees from Mines Paris and the Paris School of Economics.

Clément Boyer is a PhD student in management at Paris-Dauphine University (DRM), CIRED and the “Ecological accounting” research chair (AgroParisTech). He studies ecological accounting theory and practice and focuses on the development of ecological accounting models and methodologies. He holds a master’s degree in Sustainable Development and Organizational Responsibility from Paris Dauphine University - PSL.