C40 Events
C40 convenes mayors, city leaders, climate experts, and youth activists at events around the world to share solutions, build partnerships, and accelerate the ambitious climate action cities are delivering.
From our triennial World Mayors Summit to Climate Weeks and COP participation, these gatherings demonstrate how cities are turning climate commitments into action – protecting communities and building resilient futures.
2025 Highlights
Throughout 2025, C40 brought cities together at critical moments to drive climate action and shape global policy:
- C40 World Mayors Summit in Rio de Janeiro kicked off the COP30 Local Leaders Forum, marking 20 years of C40 Cities leadership and showcasing scalable city-led solutions (3-5 November).
- Urban 20 (U20) in South Africa put African city leadership at the centre of G20 discussions, calling for urban just transition funding that creates jobs and reduces inequality (12-14 September).
- Climate Week NYC brought together mayors showcasing bold, city-led solutions from cutting fossil fuels to creating good green jobs (21-28 September).
London Climate Action Week marked 20 years of C40 Cities and a decade since the Paris Agreement, spotlighting how mayors are redefining climate leadership in times of geopolitical instability and rising disinformation (21-29 June).
2026 Events
London Climate Action Week 2026
With more mayors, governors, and global leaders coming together than ever before, this year’s London Climate Action Week will be the biggest yet and marks a pivotal moment for city-led climate action.
2025 Events
C40 World Mayors Summit 2025
Co-hosted by the Mayor of London and C40 Cities Co-Chair Sadiq Khan and the Mayor of Rio de Janeiro Eduardo Paes, the Summit brought together mayors from nearly 100 cities alongside business leaders and civil society. Taking place 3-5 November in Rio de Janeiro, it kicked off the COP30 Local Leaders Forum and built momentum ahead of COP30 in Belém.
Climate Week NYC 2025
C40 mayors gathered at New York Climate Week to showcase bold city-led solutions, from cutting fossil fuels and scaling clean energy to creating good green jobs and protecting communities. The event took place on 21-28 September 2025.
London Climate Action Week 2025
Marking 20 years of C40 and a decade since the Paris Agreement, mayors and global leaders spotlighted how cities are stepping up with urgent climate action amid geopolitical instability and rising disinformation. This event took place on 21-29 June 2025.
C40 World Mayors Summit
C40’s flagship event driving the shift from climate commitments to action
Every three years, the C40 World Mayors Summit brings together mayors from C40’s nearly 100 cities on the frontline of the climate crisis to set the course for the next generation of city-led climate action.
At a time of growing climate impacts, geopolitical instability, and rising disinformation, the Summit demonstrates that united, cities can push the global agenda forward, mobilise the resources needed, and deliver urgent solutions to build a safer, healthier, and more equitable future for all.
Key highlights from previous Summits
- Record investment secured for C40 cities in the Global South, projected to access over $1 billion to tackle the climate emergency (2022)
- First-ever global network of city-youth climate councils launched, uniting youth leaders and mayors (2022)
- Landmark City-Business Climate Alliance launched to accelerate private sector engagement (2019)
C40 World Mayors Summit: Rio de Janeiro 2025
The 2025 Summit focused on turning commitments into action. With over 70% of C40 cities outpacing their national targets, cities are already proving that climate action works. The 2025 Summit brought cities together to help them secure the finance and build the collaborative frameworks needed to meet the urgency of this moment.
Taking place days before COP30 in Belém, the Summit:
- Marked 20 years of C40 leadership and 10 years since the Paris Agreement
- Kicked off the COP30 Local Leaders Forum, co-hosted by Bloomberg Philanthropies and COP30 Presidency, to put cities at the heart of global climate negotiations
- Showcased two decades of city-led delivery on emissions reduction
- Recognised standout climate leadership through the Local Leaders Awards
C40 World Mayors Summits
The 2025 Summit focused on turning commitments into action. Taking place 3-5 November, days before COP30, it marked 20 years of C40 leadership and kicks off the Local Leaders Forum.
The 2022 Summit united mayors, business leaders, and youth activists around pandemic recovery, wellbeing in cities, and climate finance. Key outcomes included over $1 billion secured for Global South cities.
The 2019 Summit gathered a global coalition demonstrating radical climate action. Mayors announced support for the Global Green New Deal, with 35 cities committing to clean air initiatives.
C40 Cities participates in Climate Week NYC annually with events and announcements showcasing city climate leadership. Past events include the 2024 Climate Week and virtual gatherings on the urban energy transition.
C40 Cities brings city voices to UN Climate Conferences, showcasing local climate action and advocating for city priorities. Recent participation includes COP29 in Baku, COP28 in Dubai, COP27 in Sharm el-Sheikh, and COP26 in Glasgow.
Celebrating the most ambitious, impactful, and inclusive climate projects led by cities worldwide.
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Discover the creative ways cities are taking climate action to create a safer, healthier future where everyone can thrive.
Commitments by C40 cities to drive ambitious climate results and halve fossil fuel use by 2030.
