World Mayors Summit Day 1

The World Mayors Summit 2025 opened with a powerful plenary as the Mayors of London, Freetown, and Rio de Janeiro highlighted the bold and practical steps cities are taking to drive global progress.

We recognise that now is not the time to run down the clock, but to up the pace

Today, over 30 cities announced yearly offers of action. Climate action is urgent, and we must move from negotiation to implementation. C40 and GCoM mayors are coming together ahead of international climate negotiations to commit to action over the next twelve months.

From protecting and restoring Xibeihu Lake in Wuhan to expanding natural and built shade in Phoenix, find out more about the pledges cities are taking over the next year.

Acting together with urgency and determination, we are confident that we can truly turn the tide, we can close the gap, and we can secure a safer and more resilient world for the generations to come. The yearly offer of action is the way it's going to happen.

C40 Co-Chairs, Mayor Sadiq Khan and Mayor Yvonne Aki-Sawyerr, also celebrated the news that 73% of C40 cities, for which data is available, have peaked their emissions, with 23 cities delivering a 17% reduction compared to their peak.

Mayor Khan announced that 50 mayors have committed to new clean air targets, aiming to save hundreds of thousands of lives and prevent thousands of childhood asthma cases.

Mayor of Rio, Eduardo Paes, welcomed city leaders to the beautiful city of Rio de Janeiro and set the scene for the coming days.

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.

C40's Executive Director Mark Watts celebrated the progress C40 cities have made and provided a more data-driven picture of what must come next if we are to reach our 2030 targets.

Thanks to the tremendous leadership in this room and efforts by millions of people living in C40 cities, emissions across C40 cities are now falling, despite growing populations and economies.

The Chair of UN High‐Level Expert Group on the Net Zero Emissions Commitments of Non‐State Entities, Catherine McKenna, thanked all mayors for being climate doers and not climate wreckers, and delivered the new Integrity Matters report in a conversation with Selwin Hart, Special Adviser and Assistant Secretary-General for Climate Action.

"Leadership means implementation, not intention. 10 years ago, the world was headed for 4°C of warming. Now we bent the curve closer to 2.5°C. That's not where we need to be, but it shows what's possible. Cities have been a big part of this."

COP30 Executive Director Ana Toni set out why subnational actors are so essential to deliver on COP30 priorities.

"COP30's goals can only be achieved with mayors - there's no doubt about that. That's why Brazil's own NDC has mayors and subnational leaders at the frontline. Cities are at the centre of the action in three major UN reports from last week. Action is going to give us more ambition. We need you in Belém: we need your vision, your pragmatism, and your action."

Making cities more accessible for a healthier future

Later in the day, mayors and city leaders explored how redesigning neighbourhoods for people and nature delivers health and climate benefits.

Mayor of Paris, Anne Hidalgo, and Mayor of Bogotá, Carlos Galán, shared how their cities are reclaiming streets from cars, expanding green spaces, and prioritising active, low-emission lifestyles.

"What used to be a highway is now like a new park, a central park by the river. When we act for the climate, we act for people's health, for solidarity, and for equality among citizens."

Urban Design experts from Gensler and the Inter-American Development Bank joined Mayor Hidalgo and Mayor Galán. The panel also heard from winners of the Healthy Cities Challenge and the Students Reinventing Cities competition.

Together, they discussed how designing green and thriving neighbourhoods from the ground up makes cities more accessible, family-friendly, and enjoyable for people of every age, ability, and background.

One million buildings phasing out fossil fuels by 2050

Cities are pioneering a fair, clean energy transition; from electrifying transport and buildings to scaling renewable power.

One-third of the signatory cities of C40's Renewable Energy Accelerator are now powered entirely by renewable electricity for their municipal operations. Cities have also committed to deploying one million small-scale renewable systems by 2030 and phasing out fossil fuels from over one million buildings by 2050, creating cleaner, healthier urban environments.

Across C40 cities, renewable capacity has tripled since 2000:

• Sydney and Melbourne have adopted all-electric building policies
• Cape Town is advancing renewable procurement
• Milan is expanding its Low Emission Zone

Together, these actions demonstrate how cities are leading the shift to fossil fuel-free, resilient, and healthier futures.

Scaling green innovation

With more Chinese city leaders attending the World Mayors Summit than ever before, leaders explored new models of South-South cooperation.

Cities across Africa and Latin America are working with Chinese partners to overcome financing and technology gaps, scale their green innovation, and turn ambition into implementation to reach their climate goals.

It's In The Air powered by Breathe Cities

At the Breathe Cities session, mayors highlighted how the initiative is helping them use data and community engagement to drive bold policies and deliver cleaner air for all.

From London having established the biggest clean air zone in the world, to Rio aiming for electrification of 30% of its bus fleet by 2030, they are proving that progress is not just possible, but unstoppable.

Breathe Cities is now 14 cities strong, supporting mayors and communities transforming their streets, developing clean air zones, and implementing air quality solutions.

AI: The risks and the opportunities

At a panel on artificial intelligence and digital technology, city leaders joined tech and climate experts to explore how AI can help accelerate climate action and make cities more resilient.

In collaboration with the Federal Government of Brazil, C40 Cities and GCoM launched the City Climate Compass, an AI-assisted digital dashboard that helps all 5,570 Brazilian municipalities turn their data into real solutions, offering an integrated view of greenhouse gas emissions, climate risks, and priority high-impact actions to implement.

Speakers from Google, IBM, UNEP, and Global Optimism discussed the opportunities and risks of AI with GCoM, and the need to ensure its benefits reach all cities.