Paris, France (23 June 2025) – Ten years after the landmark Paris Climate Agreement was signed at COP21, city leaders from around the world will unite at Paris City Hall today to mark a decade of progress against the odds and reaffirm their commitment to driving future climate talks from negotiation to delivery.
The event will bring together mayors, national government officials, international organisations, multilateral banks, and some of the key architects of the COP21 deal.
It comes just five months before COP30 in Belém, Brazil, widely seen as the world’s best opportunity to realign efforts to halve emissions, phase out fossil fuels, and meet urgent 2030 goals on energy, equity, and resilience. C40 Co-chair Mayor Sadiq Khan will address one of the key themes set out by the COP30 Presidency as he delivers a keynote speech on the dangerous rise of misinformation and the vital link between climate, democracy, and justice. Mayor of Rio de Janeiro, Eduardo Paes, will emphasise the vital work of his country in preparing to host a COP that it is hoped will usher in a ‘decade of delivery’.
The event will also emphasise the links between climate and the protection of truth and science in a polarised political landscape. Delegates will hear from American mayors, including Phoenix’s Kate Gallego, who are committed to climate action despite federal opposition and demonstrate that local authorities still have the power to bring about change.
By 2050, more than 70% of the world’s population will live in cities, which will account for more than 80% of greenhouse gas emissions. Cities are at the heart of the global response to the climate emergency, often moving further and faster than their national counterparts. More than three-quarters of the members of the C40 Cities network (nearly 100 of the world’s leading cities committed to climate leadership) are cutting per capita emissions faster than their national governments. All C40 cities have action plans aligned with Paris targets as a condition of membership.
A new exhibition at Paris City Hall, ‘From Paris to Belém, 10 years of urban transformation’ charts how mayors are improving people’s lives, through cleaner air, more accessible public space, and green jobs, while driving down emissions and boosting resilience.
A delegation of C40 mayors will then travel to London by Eurostar to take part in London Climate Action Week, the largest city-wide climate festival in Europe, and another crucial staging post for coordinating city climate action on the road to COP30.
Mayor of Paris, Anne Hidalgo said: “Ten years ago, the world came together in Paris to face down the growing threat of the climate emergency. Since then, our city and mayors around the world have made real progress, not just in cutting emissions, but improving lives.
“Cleaner air, safer streets, better housing, green jobs: these are the results of determined and effective climate leadership. The signing of the Paris Agreement in 2015 was a moment of global optimism. It is essential we capture that spirit again at COP30, ensuring that effective climate action happens every day, not every decade.”
Mayor of Rio de Janeiro, Eduardo Paes said: “When it comes to tackling the climate crisis, no one is better positioned to lead on implementation than mayors and local governments.
“In Rio, we’ve made major strides over the past decade, expanding clean and renewable energy, improving high-capacity public transportation, and launching Brazil’s first heat protocol, to name a few.
“As COP30 comes to Brazil, we carry the hopes of millions across Latin America and the Global South—regions that have contributed the least to this crisis but suffer its consequences the most. This must be a COP of delivery, not delay. It’s time to empower cities, unlock climate finance, and ensure that climate justice becomes a lived reality, not just a rhetoric.”
Mayor of Phoenix, Kate Gallego said: “In Phoenix, the need for continued climate action is evident in our intensifying summer heat, aridification that threatens our water supply, and air quality issues that impact public health. We don’t have time for denial or political showmanship, and delaying necessary investments only makes these issues more expensive and difficult to address. Climate leadership is economic leadership.
“While our current federal administration backtracks, cities across the country continue to make progress for the benefit of our residents, public health, and economy. We’re cutting emissions, modernizing our infrastructure, and protecting our communities from extreme weather because it’s what the moment demands and what our residents deserve.
“At COP30, we need the global community to recognize what mayors already know: climate action must be local, urgent, and accountable– and cities are leading the way.”
Gwendoline Cazenave, CEO of Eurostar said: “It’s an honour to welcome so many mayors who have chosen the greenest route to London with Eurostar – a powerful statement of their commitment to sustainable travel.
“With the Eurostar teams, we are steadfast in our mission to build the backbone of sustainable travel across Europe, not only by expanding our network but by championing the growth of international rail.
“Together, we’re taking actions for a greener future; for our communities, our climate and the next generation.”
Mark Watts, Executive Director of C40 Cities said: “Cities have been the driving force behind the most ambitious and effective action towards preventing climate breakdown since the Paris Agreement was signed.
“But our work is far from done. With COP30 on the horizon, cities are ready to work with national governments to help move COPs from negotiations to implementation and to scale climate solutions that protect lives, grow local economies, and advance social justice.”