Mayor of London Sadiq Khan and Mayor of Rio de Janeiro Eduardo Paes welcomed 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, while 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 showing that emissions in 73% of the organisation’s member cities (for which data is available) have already peaked and are now declining.
This demonstrates that rapid and sustained decarbonisation is possible even as economies and populations continue to expand. Eleven cities have cut their emissions by more than 30 per cent since their peaks, and C40 data show that cities in the network are collectively reducing per-capita emissions five times faster than the global national average.
These results demonstrate that climate action can deliver tangible benefits 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 around the world will today outline not only 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, 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-centred 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 outline her vision for the future of global climate cooperation, with cities driving the level of ambition and action required.
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, highlighting the vital role cities are playing in 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 20 years ago, on the understanding that the climate emergency was a global emergency that required cities to work together and learn from one another. This led to the establishment of several ‘accelerators’ that bring together cities from different countries facing similar climate issues to learn from one another.
One of the most successful such accelerators is the Clean Air Accelerator, launched six years ago by 35 cities, now expanded to 51, led by Mayor Sadiq Khan, with commitments aligned with WHO guidelines. Cities in the network have made a significant leap forward in their pollution monitoring capabilities, expanding from 250 PM2.5 sensors in 2019 to more than 1,600, and from 49 NO₂ sensors to nearly 900 across the same 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
