Opinión CIDOB nº 769

Climate-diligent cities: Aligning mitigation ambitions with the Paris Agreement

Publication date:
Didac Amat, PhD candidate in International Climate Law, Pompeu Fabra University (UPF) and Ricardo Martinez, Senior Research Fellow, Global Cities Programme, CIDOB

City governments are often more ambitious than their national counterparts in terms of GHG emission reduction goals. Yet the formal rules underpinning the international regime and guiding the climate action of nation-states are not incorporated by cities. The time to set the urban climate standard of diligence has come.


Almost 300 hundred years after the steam engine emitted the first CO2 molecules and catapulted urban areas towards industrialization, the acceleration of climate change is self-evident. However, the droughts in Europe, the wildfires in Chile, or the Pakistan floods are just the beginning. As a gradual event, the consequences of global warming will be more extreme as the emission of greenhouse gases (GHG) and their atmospheric concentration continue to grow.

But how much can we emit before exceeding the safe threshold? During the last decades, the IPCC has determined the remaining carbon budget. If we want to avoid the most critical climate scenarios, from 2020 on, humanity can only emit 500Gt of CO2 net emissions. While this amount may seem gigantic, by 2019, the world emitted 52.6 Gt. Therefore, at the current level, we will have consumed the entire budget by 2030.

However, it is well-known that emissions are not equally distributed among and within countries. Altogether with the historic North-South division, there are huge differences between the emissions from rural and urban areas, with the IPCC considering cities responsible for 67-72% of the global emissions. Indeed, city governments are also failing future generations.

During the last decades, this evidence has led several cities to adopt climate-sensitive strategies. This is particularly the case of climate-oriented city networks through which local governments amplify urban climate action and seek to contribute to the objectives of the international climate regime. For instance, the Global Covenant of Mayors for Climate & Energy (GCoM), the world’s largest alliance with over 12,000 members, estimates that the climate mitigation objectives adopted by their signatories will reduce global emissions by 4.1 GtCO2eq by 2050. As such, the GCoM signatories have demonstrated to go further and faster than their respective Nationally Determined Contributions (NDCs). With countries unable - individually and collectively - to rise to the challenge, the climate mitigation objectives adopted by city governments constitute an essential part of the highly necessary comprehensive response to the climate emergency. 

In overall terms, city governments are hence more ambitious than their national counterparts in terms of GHG emission reduction goals. Manchester, for example, has committed to a carbon budget of 3.6 million tonnes between 2023 and 2027. Similarly, Johannesburg has announced a 43% reduction of Business as Usual (BAU) emissions by 2030. But is this enough to fulfill the urgent measures needed to limit the temperature increase to 1.5 °C as the Paris Agreement pledges? Are 3.6 million tonnes too much for Manchester? Is 43% sufficiently ambitious for Johannesburg?

The truth is that there are several tools to monitor the mitigation strategies of nation-states and to determine their fair share. However, we lack information and instruments to assess whether a city is doing enough to combat global warming, making it harder for citizens to exercise their democratic rights and hold their governments accountable.

In this context, we advocate for the notion of climate-diligent cities. According to this concept, a diligent city is one which deploys the adequate means and best feasible efforts to reduce its net emissions. In line with the expectations that the Paris Agreement sets on countries, diligent cities are those whose contribution reflects their highest possible ambition.

However, determining when a mitigation plan observes these two requirements is challenging. We here lay out a conceptual framework as the first step of a broader effort towards defining such a climate standard of diligence. It is evident that cities are not immune to the historical differences between the global North and the global South, nor do they all have the same resources and capacities to mitigate global warming. Nonetheless, thirty years of international climate negotiations have established mechanisms to incorporate such differences. As the UNFCCC and the Paris Agreement prescribe, climate mitigation and adaptation strategies must consider the principle of Common but Differentiated Responsibilities and Respective Capabilities (CBDR-RC)in the light of the different national circumstances. If such an international principle guides the climate action of nation-states, city governments can legitimately adapt their ambitious urban strategies and align them with the formal rules underpinning the international climate regime.

The conceptual framework of the climate standard of diligence for cities should rest on three propositions deriving from the state-based CBDR-RC principle. Firstly, global warming is a common responsibility. Therefore, while contextual factors will modulate the individual contribution of each city, all local governments must deploy adequate mitigation means and their most ambitious efforts.

Secondly, the CBDR-RC principle also establishes that, while common, the responsibility of each city government is different. Inasmuch as Northern cities have contributed the most to historical emissions, their climate ambition should be higher. Hence, Southern cities would own most of the remaining urban carbon budget.

Finally, the third conclusion recognizes that ambition levels strongly rely on each city’s assets, capabilities, and circumstances. Therefore, we cannot use the historical contribution as the only yardstick, but we must accept that achieving carbon neutrality may take longer in cities with fewer resources. Accordingly, the CBDR-RC not only modulates climate ambition between Northern and Southern cities. It also distributes climate ambition within each of these groups.

In this regard, international transfers like the C40 promise to spend two-thirds of its budget supporting climate action in global South cities should help to partially strengthen their mitigation commitments. To the extent that resources, capabilities, and circumstances are unique and dynamic, so are the levels of climate ambition. Accordingly, we cannot determine the diligence standard of each city by only using the historical emissions or the fixed binary division between the global North and the global South. By contrast, we should design more complex variables capable of setting individual urban ambition levels and mechanisms to adjust them to the cities' time-changing circumstances.

To conclude, by 2023, the critical role of cities in limiting global warming to 1.5ºC is undeniable. However, since urban areas are responsible for most of today's global emissions, climate-sensitive cities are no longer enough. Only climate-diligent cities, those that deploy adequate means, put forth their best possible efforts, and reflect their greatest possible ambition to mitigate climate change, will be part of the solution. The time to set the urban climate standard of diligence has come.

Keywords: cities, climate, mitigation, Paris Agreement, emission reduction, IPCC, GCoM, UNFCCC, CBDR-RC, North-South division

All the publications express the opinions of their individual authors and do not necessarily reflect the views of CIDOB as an institution.