- 9th C40 World Mayors Summit begins with cities joining Brazilian COP Presidency’s Global Mutirão and calling for a ‘decade of delivery’
- New data shows emissions in 73% of C40 cities have peaked and are now declining
- Mayors present their ‘yearly offers of action’ pledging to take bold steps to protect their residents and the planet in the next 12 months
- Two new Accelerators launched to establish mayoral commitments to tackle urban heat and develop sustainable food systems by 2030
- Members of Clean Air Accelerator to announce new targets of saving over 450,000 lives by 2040
Rio de Janeiro, Brazil (3 November 2025) – Mayor of London Sadiq Khan and Mayor of Rio de Janeiro Eduardo Paes will welcome more than 300 of their fellow city leaders to the C40 World Mayors Summit in Rio today with a single clear message: it is time to move from the era of climate negotiation to the decade of delivery, with cities taking the lead.
The C40 World Mayors Summit 2025, part of the Bloomberg Philanthropies COP30 Local Leaders Forum, will bring together city leaders from five continents. They stand united in their commitment to protect their residents from the dangers of the climate emergency whilst also utilising climate progress to improve livelihoods, create fairer societies and boost their local economies. The Local Leaders Forum is the official sub-national pillar of COP30 and the first time sub-national leadership has been recognised as a key part of the COP process.
C40 cities have already made huge progress in turning the tide on their negative environmental impact, with new research (see ‘Notes To Editors’ for link to the full report) showing that emissions in 73% of the organisation’s member cities (for which data is available) have already peaked and are now declining. This is proof that rapid, sustained decarbonisation is possible even as economies and populations expand. Eleven cities have cut emissions by more than 30 per cent since their peaks, and C40 data shows cities in the network are collectively reducing per-capita emissions five times faster than the global national average.
These results show that climate action can deliver results to protect the people and places we love, not just in the future but today. In this spirit, and reflecting COP30’s goal of moving from ‘negotiation to implementation’, mayors from across the world will today set out not just what they have achieved, but also what they will do in the next twelve months.
This ‘yearly offer of action’ ties in to the Brazilian COP30 Presidency’s call for a Global Mutirão – a collective effort to deliver on climate commitments – and adds urgency and accountability to the climate promises made by elected officials. By delivering practical actions rooted in science and centred on people, mayors are bringing the real-life benefits of climate action directly to city residents, creating good green jobs, affordable housing, cleaner air, healthier streets, and safer places to live.
Co-Chair of C40 Cities, Mayor of London Sadiq Khan said: “Mayors are not waiting for others to act. Across the C40 network, we are proving that local leadership delivers real results, from cleaner air and healthier streets to fairer, stronger local economies.
“Twenty years after C40 was established, our cities are cutting emissions faster than national governments and showing that progress is possible. We’re leading from the front, protecting residents, creating good green jobs and showing that climate leadership can improve lives for every community.
“We need national governments around the world to follow suit. This must be the decade of delivery, where ambition is matched by action.”
Mayor of Rio de Janeiro, Eduardo Paes said: “Hosting the World Mayors Summit here in Rio is a proud moment for our city and for Brazil.
“We know what it means to face climate risks, but also the opportunity that comes with action. Brazil’s hosting of COP30 will show that cities can deliver results now, not in the distant future.
“Through collaboration across C40 and the Global Mutirão, we are proving that mayors can turn ambition into reality, building cleaner, fairer and more prosperous cities for our people and for generations to come.”
Co-Chair of C40 Cities, Mayor of Freetown Yvonne Aki-Sawyerr OBE, said: “Floods, food insecurity, and deadly heat are not future risks. For many cities, especially across the Global South, they are our present reality.
“That is why we cannot wait for change; we must drive it ourselves. The climate actions showcased over the next two days, together with the launch of pioneering projects such as the Cool Cities and Thriving Food Systems Accelerators, demonstrate what is possible when cities lead and local communities are empowered to act. Our focus is on practical, people-centred solutions that save lives, build resilience, strengthen our economies, and create opportunities for everyone, especially the most vulnerable.”
Antha Williams, Environment Programme lead at Bloomberg Philanthropies, said: “Cities are proving what’s possible on climate change, and the C40 World Mayors Summit demonstrates exactly how local leadership drives global progress.
“For more than a decade, Bloomberg Philanthropies has supported C40 and city-led climate action because we’ve seen time and again that mayors deliver results: cleaner air, healthier communities, and stronger local economies.
“The fact that emissions have already peaked in most C40 cities shows what’s possible when local leaders have the tools and support to act. As we look toward COP30 in Belém, the World Mayors Summit and COP30 Local Leaders Forum are showcasing the practical, people-centered solutions that turn ambition into reality and build momentum for even greater action ahead.”
Alongside mayors Khan and Paes, the Summit’s opening plenary is set to be addressed by COP30 Executive Director Ana Toni who is expected to set out how she sees the future of global climate cooperation with cities driving the level of ambition and action needed. Delegates will also hear from UN Special Adviser on Climate Action Selwin Hart alongside former Canadian Environment Minister and now Chair of the UN High-Level Expert Group on the Net-Zero Emissions Commitments of Non-State Entities, Catherine McKenna, who will present her latest Integrity Matters Report showing the vital role cities are playing on climate action.
Special Adviser and Assistant Secretary-General for Climate Action at the United Nations, Selwin Hart said: “In the decade since the adoption of the Paris Agreement, cities have proven that ambitious climate action delivers – driving jobs, growth and cleaner air. Even amid global divisions and tensions, C40 mayors have shown what cooperation and collaboration across borders and sectors can achieve. As the world turns to COP30 we must launch a decade of acceleration, implementation and delivery – one in which the leadership of local leaders will be essential.”
Executive Director for Brazil’s COP30 Presidency, Ana Toni said: “Cities are where the impacts of climate change are felt most directly and where some of the most innovative solutions are already taking shape. Our Global Mutirão is a call for collective action, and mayors and governors are answering that call with energy, commitment, and results. With cities and states helping us lead the way, we can make this the decade when ambition is finally turned into delivery.”
Mark Watts, C40 Executive Director, said: “This year we celebrate 20 years of C40. In 2005, a small group of forward-thinking mayors created this organisation because they feared no one else would act.
“Today, the results speak for themselves. 73% of our cities, for which we have data, have peaked their emissions, cutting faster than national governments and proving that climate leadership works.”
C40 was established twenty years ago on the understanding that the climate emergency was a global emergency that required cities to work together and learn from each other. This led to the establishment of a number of ‘accelerators’ bringing together cities from different countries facing the same climate issues to learn from each other.
One of the most successful such accelerators has been the Clean Air Accelerator, launched six years ago by 35 cities, now expanded to 51, led by Mayor Sadiq Khan, with commitments aligned to WHO guidelines. Cities in the network have taken a huge leap forward in the way they monitor pollution, expanding from just 250 PM2.5 sensors in 2019 to more than 1,600, and from 49 NO₂ sensors to nearly 900 across the same time period.
Announcing a new collective goal today, the accelerator member cities will pledge to save over 450,000 lives from air pollution across their cities by 2040, gaining 5.4 million years of life, and save over $840 billion by reducing air pollution to meet their air quality targets.
Meanwhile, the two newest global accelerators will be launched today, targeting two of the most urgent climate concerns facing cities today:
- The Cool Cities Accelerator responds to the UN Secretary-General’s Call to Action on Extreme Heat, committing mayors to protect lives and redesign their cities to address rising urban heat. Cities will establish heat governance teams, early-warning systems and public cooling networks while also transforming buildings and streets with green roofs, shade and water features. 33 cities from across Asia, Africa, Europe, and the Americas are united to protect residents and transform urban spaces for a hotter future by 2030. The accelerator was established with the support of the Rockefeller Foundation.
- The Thriving Food Systems Accelerator supports cities across Africa, Asia and Latin America to ensure access to nutritious and affordable food that is sustainably produced. Cities commit to providing a daily healthy meal for every child, upgrading markets, cutting food waste and creating good green jobs with the surrounding municipalities.
Together, these accelerators show how cities are turning science into delivery and delivering on COP30’s goal of implementing practical solutions that protect the most vulnerable.