The role of cities in the pursuance of the Paris Agreement

The C40 Cities Climate Leadership Group is already in existence for more than 12 years and represents 96 of the world’s greatest cities with together more then 650 million inhabitants (March 2918).

The group is making every effort to ensure that its member cities contribute proportionately to the Paris Agreement. The Paris Agreement commits signatories holding the increase in the global average temperature below 2 degrees above pre-industrial levels and to pursue efforts to limit the temperature increase to1.5 degrees above pre-industrial levels. Actually this commitment includes two scenarios.

C40 has published three solid reports – together with Arup and McKinsey – that provide a roadmap towards the above mentioned goal, preferably the 1,5 degrees Celsius trajectory.

The first report is Climate Action in Megacities 3.0. (December 2015), an account of the accomplishments of C40 cities in the decade before the Paris Agreement. The second one Deadline 2020: How cities will get the job done. (December 2016) suggests necessary actions in the period 2016 – 2020. The third one Focused acceleration: A strategic approach to climate action in cities to 2030. (November 2017) is emphasizing the necessity of focusing and accelerating actions in the next decade.

These reports provide insight into the ultimate challenge of the Paris Agreement and the road towards its eventual accomplishment. They are a must to be consulted by anyone who is involved in urban energy policy. Reading the brief account below might be a substitute or – better – an appetizer.

1 The world is already in danger

Global warming is a direct consequence of the emission of CO2 above the critical level of 350 ppm (parts per million). At this time the global emission level is 400 ppm. Global temperatures have already increased by 1 degree Celsius from pre-industrial level. The diagram below depicts the main sources of urban emission: buildings, transport and waste.


2 Growth of CO2 emissions under conditions of ‘business-as-usual’

Without any further climate actions beyond the 2015 level, global emissions in C40 cities will rise seven times during the 21th century.


3 The effects of global warming

At this time representatives from C40 cities already refer at observable climate changes. The graph below depicts the character of these changes.

As a consequence of these changes, cities face several different types of hazards. Extreme temperature and flooding account for 63% of all hazards reported globally. North American cities experience more temperature hazards (40%) than other regions. European cities report the highest proportion of flooding hazards (30%). 62% of all land movement hazards were reported by Latin American cities. 63% of all water scarcity were in either North American or European cities.

It has have been estimated that by 2050 global warming related disasters will put 1.3 billion people and assets worth $158 trillion at risk. In addition to efforts to reduce carbon emissions the Paris Agreement commits signatory nations to a common effort of enhancing adaptive capacity, strengthening resilience and reducing vulnerability to climate change.

4 CO2 emissions have to be zero after 2050

The graph below is disclosing at one hand the expected growth of CO2 emissions without any intervention by climate actions (BAU; business as usual) beyond the 2015 level and at the other hand their stepwise phasing-out due to determined policy. The C40 cities’ emissions need to bend from an increase of 35% by 2020 to peak at only a further 5% higher than current emissions.

The next four years will determine the feasibility of the contribution of the world’s largest cities to the Paris Agreement. In 2020, C40 cities’ annual emissions target is 0.7 GtCO2e below the business-as-usual emissions, requiring accumulative savings from 2015 of 1.9 GtCO2e.

The Paris agreement kept open the door for a more risky 2 degrees trajectory, which is running parallel with the 1,5 degrees trajectory until 2030. In case of a 2 degrees Celsius trajectory zero emissions will be realized after 2050.

5 The C40’s emission budget

In 2015 the global level of emissions was 47 GtCO2e. The remaining global emissions budget until 2100 is 387 GtCO2 (at the 1.5 degrees trajectory). In 2015 the emissions of the C40 Cities were 2.4 GtCO2e. As a consequence the remaining C40 budget is 22 GtCO2e from to date until 2100. The emissions after 2050 are supposed to be zero (at the 1,5 trajectory). In case of a 2 degrees Celsius trajectory, the C40 cities’ budget is 67 GtCO2e.

Following the 1,5 degree Celsius trajectory, the average per capita emissions across C40 cities have to drop from over 5 tCO2e per capita today to 2.9 tCO2e per capita by 2030.


6 Negative emissions

The 1.5 degree target trajectory hits zero emissions by 2050 and has to continue until 2100 with negative emissions. A zero emission level in 2050 unfortunately does not mean that the production of CO2 has vanished. In the 1,5 degree Celsius trajectory from now until 2100 31 GtCO2e will be produced on top of the budgeted 22 GtCO2e. This has to be stored and eliminated eventually.

Since carbon capture and storage is not yet widely employed there is an enormous amount of work to be done to make this trajectory a reality. A range of negative emissions technologies is currently under scientific research and evaluation. These capture CO2 from the air directly or indirectly, and permanently store it in underground reservoirs or in other stable forms for geological timescales.

Without negative emissions our calculations suggest that zero net emissions would need to be reached in C40 cities as early as 2030.

7 Contribution of cities is variable

Wealthier, high carbon cities must deliver the largest savings between 2017-2020. Cities with GDP over $15,000 per capita must begin to reduce their per capita emissions immediately. Cities with a steep decline trajectory are required to make considerably larger savings in the early years. By 2020 these cities need to save between two and five times as much as any other group. By 2030 the peaking cities need to take a step change through transformative action. They will benefit from the lessons learned by the declining cities, reducing per-capita emissions in the later decades at similar paces to declining cities in the early decades.




8 Decreasing emissions by targeted actions

The C40 cities have adopted a strategy of targeted actions to reduce the effects of climate change (mitigation) and to cope with them (adaptation). Between 2005 and 2016 nearly 11.000 unique actions have started with respect to adaptation, buildings, community-scale development, energy supply, finance, food & agriculture, mass transit, outdoor lighting, private transport, waste and water.

In 2015, 30% of climate actions were delivered as a result of collaboration with other cities, mostly C40 cities.

The Green Digital Charter collected 24 case-studies for 21 contributing cities in a booklet. This booklet depicts the ingenuity of many actions and at the same their rather small scale.

Green Digital Charter (GDC) collection of case studies 2017


GDC signatories are leading the way in deploying digital solutions to reduce their carbon footprint and improve their citizens’ quality of life. Buildings, energy, transport, e-participation, green ICT, waste management: This third publication gathers inspiring (and replicable?) solutions.

In the four years to 2020, an additional 14,000(!) actions of a comparable scale are required. An alternative are less and bigger actions.

9 Towards a focused acceleration 

The costs of most (54%) actions are below $1 million. At the other hand one in four actions have received capital investment of more than $10 million. Apart from their rather small size C40 has realized that these actions are dispersed over a myriad of topics. At current rates of implementation and adoption these actions are set to deliver only a 20 to 50 percent decrease of the emissions through 2030. Therefore many cities with climate actions in place are currently falling short of a 1.5°C trajectory.

As a consequence cities are recommended to switch to a strategy of focused acceleration within 12 fields of action, belonging to four groups:

  • Decarbonizing the electricity grid
  • Optimizing energy efficiency in buildings
  • Enabling next-generation mobility
  • Improving waste management

The chart below is a short description each of the four groups and the 12 fields of action



10 A differentiated approach of types of town

To demonstrate the scale of action needed to achieve the full city’s emissions-reductions target by 2030, C40 has modeled sample road maps for six illustrative city types varying in size, income and density. These road maps demonstrate the practical impact of focused acceleration across different types of cities. An overview of two roadmaps is disclosed below. The other maps can be consulted in the report Focused acceleration.


11 The power of the city is not unlimited

Cities can deliver or influence just over 50 percent of the savings needed to keep a 1.5 degree trajectory either through their own direct action or through collaboration with the private sector. This means that action to deliver structural changes from outside cities (i.e. electrical grid decarbonization), must start right now to have a significant impact from 2023 at the latest. This will become the dominant driver of urban CO2 reductions after 2030.

An additional option is active engagement of cities in district thermal systems, possibly as public-private partnerships.

An additional problem is that the use of electricity is growing faster than anticipated, partly because of the towering deployment of digital equipment for a myriad of applications.  The American Council for an Energy-Efficient Economy (ACEEE) recently released its 2017 City Energy Efficiency Scorecard.. In a host of frequently lauded cities, building electricity use is up in Los Angles (+3 percent); New York City (+1 percent); San Francisco (+1 percent); Boston (+2 percent); Denver (+3 percent); Austin (+5 percent); and D.C. (+1 percent).

12 Investments

The accomplishment of zero carbon emissions in 2050 is requiring huge investments, roughly $50 to $200 per ‘saved’ metric ton of CO2 equivalent. Otherwise, these investments come with a global  $16.6 trillion global economic opportunity.

From 2016 to 2050 each C40 city in Europe will have to invest $ 10 billion to meet the ambition of the Paris Agreement. This is over $1 trillion investment across all C40 cities. $ 375 billion of this investment is needed over the next four years alone to take the climate action required.

13 Other towns

Should all global cities population greater than 100,000 adopt the roadmap that has been set out for C40 cities, the cumulative effect would be 40% of the emission reductions required to keep temperature rise below 1.5 degrees. As a consequence there is a potential to save 863 GtCO2e globally by 2050.

14 Summary

From a starting point of 2.4 GtCO2e greenhouse gas emissions by C40 cities in 2015 emissions have the potential to rise almost sevenfold by 2100 if no further climate action is taken. Commitment to a 1.5 degree future is requiring that C40 cities limit emissions to 22 GtCO2e between to date and 2100. In addition they have to contributing to global negative emissions efforts, removing 31 GtCO2e from the atmosphere in the second half of the century.

Climate action enable C40 cities to save a total of just over 500 GtCO2e versus the business-as-usual trajectory by 2100. However while these actions represents an impressive 51% of the savings necessary, cities will be reliant on external actors and events to achieve the full transition to zero and beyond.

Of the 51% of reductions achieved, 20% of the necessary actions can be implemented by cities unilaterally while the remaining 80% can be delivered through a combination of collaboration and partnerships.


After the retirement of the president of the USA from the Paris Agreement many cities in the USA and globally announced that they would compensate for the declining support from federal level in the USA. The C40 cities in particular are determinate to contribute significantly to the success of the Paris Agreement and have produced detailed plans to act accordingly. At the same time C40 cities have made clear that they are reliant on external actors and events to fulfill their ambitions.

I must admit that while studying the C40 plans the degree of external reliance exceeded my expectations and dampened my optimism as well. Mayors can buy as many electric busses as they want but the efficacy of electrification is limited without decarbonisation of the grid. And this is largely beyond their influence.

Meanwhile cities are faced with tremendous tasks, for instance:

  • Decarbonisation of traffic and transport;
  • Massive deployment of district heating (and cooling);
  • Supporting initiatives with respect to local production of sustainable energy ;
  • Substantial lowering of energy-use in new and retrofitted property and in lightning.

I am pretty sure that the 1,5 degree Celsius trajectory is attainable only by tight cooperation within cities between all actors, citizens not to forget and – at country level – between cities, industry, energy producers and government.

Anyway all actors involved can mirror the excellent performance of C40 cities by initiating climate actions more then ten years ago.

*) This article was brought to you by Professor Herman van den Bosch, Professor at Open University of The Netherlands.

Herman van den Bosch


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