Turning climate ambition into reality
Across the world, cities and their mayors are driving climate solutions forward. At a time when many national governments are pulling back on their commitments, cities are stepping up. They’re showing what determined, joint climate action looks like to protect the people and places we love.
With over 700 events and more than 45,000 attendees, London Climate Action Week 2025 captured this spirit perfectly as Europe’s largest city-wide climate festival. As C40 Cities celebrated its 20th anniversary, it was a chance to see how far cities have come – from cutting emissions and improving public health to cleaning the air and building resilience – and to look ahead to major milestones still to come later this year.
The week also marked the 10th anniversary of the Paris Agreement with a powerful message: “Behind every climate solution is a community and a city that dared to lead”. At Paris City Hall, mayors reflected on progress across key issues and set ambitious goals for 2030 and 2050. In a show of unity, mayors then travelled together by Eurostar from Paris to London. Standing side by side on the platform, they showed how closely cities are working across borders to accelerate climate action.
From negotiation to delivery
All'inizio della settimana, C40 Co-Chair and Mayor of London, Sadiq Khan, announced that the next C40 World Mayors Summit will take place in Rio de Janeiro this November. The summit will put local leadership at the centre of global climate talks. As part of the COP30 Local Leaders Forum, co-hosted by Bloomberg Philanthropies and the COP30 Presidency, it’s a crucial opportunity to shift negotiations to delivery at what many consider the most important climate summit in a decade.
In un evento ospitato da C40 Cities and the UK’s Foreign, Commonwealth & Development Office, mayors shared how local initiatives are scaling globally. From Nairobi’s solar-powered markets to Medellín’s big push on energy efficiency, the results speak for themselves. 82% dei C40 cities are already outpacing their national governments on climate targets, but to go further, we must work together. That urgency was echoed later in the week when C40 Cities and the Global Covenant of Mayors released the “From Paris to Belém” report, underscoring how local leadership is closing the gap on national climate promises and driving the just transition forward.
Financing the future we need
Above all, the week showed how climate action is already transforming daily life. Cities aren’t waiting for the next global summit; they’re getting on with the work now.
London has the world’s largest clean air zone and the biggest zero-emission bus fleet in Western Europe. We’ve planted 600k trees, and invested in clean energy and cycling.
C40 Co-presidente e sindaco di Londra, Sadiq Khan
Mayors shared how local action is improving public health, protecting communities from extreme weather, and creating fairer, more liveable cities. Mayor of London, Sir Sadiq Khan, launched a new Climate Finance Taskforce to help the city raise the funds needed to reach net zero by 2030. At the same time, a green finance roundtable brought together city leaders and global investors to explore how to unlock investment that can transform urban life.
We’re cutting emissions, modernising our infrastructure, and protecting our communities from extreme weather because it’s what the moment demands and what our residents deserve.
Mayor of Phoenix, Kate Gallego
Big partnerships were also front and centre. C40 Cities and Uber announced plans to roll out EV charging for more than 55,000 drivers, making it easier for people to switch to cleaner transport. C40 Cities also announced a new strategic partnership with Ramboll Foundation, which builds on a long-standing relationship with the Ramboll Group. The collaboration will help cities embed resilience and climate adaptation into long-term planning, governance, and policy.
Meanwhile, events hosted by Community Jameel and Gensler, and a mayoral exchange led by Arup and The Centre for Liveable Cities, explored what future-ready, inclusive cities could look like.
Più forte insieme
Throughout the week, one theme kept coming up: the need to protect climate action from disinformation. In a joint op-ed, C40 Co-Chair and Mayor of London, Sadiq Khan, and Mayor of Paris, Anne Hidalgo, warned how well-funded, coordinated campaigns are undermining trust, slowing progress, and harming the most vulnerable. Tackling this is now a key part of C40 Cities’ work on the road to COP30, to make sure climate action stays rooted in truth, justice, and protects the people and places we love.
Sullo sfondo di C40 Cities’ 20th anniversary, London Climate Action Week was a timely reminder of how far cities have come and how ready they are to go even further. As cities look to the 2025 C40 World Mayors Summit and COP30 in Brazil, the message couldn’t be clearer.
The time is now to act for a future where we are stronger together.