London and Rio de Janeiro (June 24 2025) – The Mayor of London and Co-Chair of C40 Cities Sadiq Khan and Mayor of Rio de Janeiro Eduardo Paes today announced that Rio de Janeiro will host the 2025 C40 World Mayors Summit from 3-5 November, just days before pivotal climate negotiations begin at COP30 in Belém. The Summit will kick off the Local Leaders Forum, co-hosted by Bloomberg Philanthropies and COP30 Presidency, placing subnational voices at the center of the COP30 process and elevating bold, scalable climate solutions from global mayors and subnational leaders.
Held every three years, the C40 World Mayors Summit (WMS) brings together mayors from C40’s nearly 100 cities with business leaders, philanthropists, investors, academics, and civil society to showcase how cities are delivering urgent, inclusive, and ambitious climate action. Past C40 Summits have been hosted by London, New York, Seoul, São Paulo, Johannesburg, Mexico City, Copenhagen, and Buenos Aires, marking a rich legacy of global leadership and collaboration.
As part of this year’s C40 Summit, the Local Leaders Awards Ceremony, co-hosted by C40 and Rio Mayor Eduardo Paes, will take place on 4 November. Across a number of COP30 priorities – including just energy transition, adaptation, health, and multilevel partnerships – the event will recognize one Brazilian and one global subnational government driving results in each category.
The Mayor of London and C40 Co-Chair, Sadiq Khan, said: “The C40 World Mayors Summit in Rio de Janeiro will be a defining moment for city-led climate leadership on the road to COP30.
“Cities are already delivering practical, urgent solutions to the climate crisis: cutting emissions, creating green jobs, and improving the lives of our residents. In this pivotal year, I’m proud to convene a summit that will champion city leadership and send a clear message: that in the face of growing climate denial and delay, mayors are stepping up.”
Building on global momentum and two decades of C40 city leadership, the Summit will chart what’s working and set a clear course for what’s next. In the face of global political uncertainty and growing resistance from climate delayers and deniers, the C40 WMS will demonstrate what’s possible through delivery-focused collaboration, highlighting real progress from national-subnational partnerships like the CHAMP initiative and showing that cities are not just contributing to climate solutions, but leading them.
Mayor of Rio de Janeiro, Eduardo Paes, said: “Hosting the 2025 C40 World Mayors Summit here in Rio de Janeiro, on the eve of COP30, is a moment of great pride for our city and our country. This event brings together global urban leaders at a crucial time for our planet, underscoring the vital role cities play in confronting the climate crisis.
“Cities are on the frontline facing its impacts daily and pioneering solutions that protect communities make our residents’ lives better and safer. This Summit will amplify the power of local action and showcase how, together, cities can push the global agenda forward, mobilising the resources and partnerships needed to build a safer, healthier, and more equitable future for all.”
Mayor of Freetown and C40 Co-Chair Yvonne Aki-Sawyerr OBE said: “The C40 World Mayors Summit in Rio is a critical platform to amplify the voices of youth and communities on the frontlines of the climate emergency. Young people are not only demanding change, they are leading innovation and driving powerful solutions in cities across the Global South. However, to turn ambition into impact, we urgently need greater climate finance and investment that reaches the places bearing the brunt of this crisis.
“This Summit will send a clear message: real climate leadership requires both local action and global solidarity, with equitable resources to ensure no city or community is left behind.”
Michael R. Bloomberg, UN Secretary-General’s Special Envoy on Climate Ambition and Solutions and Founder of Bloomberg L.P. and Bloomberg Philanthropies, said: “Cities are confronting the accelerating effects of climate change by cutting emissions in ways that also protect public health and strengthen local economies. The C40 World Mayors Summit in Rio will spotlight the progress cities are making and help ensure their voices are heard at COP30.”
As part of the Local Leaders Forum, hosted by COP30 President André Corrêa do Lago and Michael R. Bloomberg, UN Special Envoy on Climate Ambition and Solutions and C40 Board President, the Forum will ensure that local priorities and solutions are firmly on the table before global leaders begin formal climate negotiations. Over three days in Rio, it will spotlight bold local solutions, mobilize climate finance, and align local action with global goals—from tripling renewable energy by 2030 to improving public health and cutting emissions. The Forum will also help drive progress toward the COP29 target of mobilizing at least $1.3 trillion annually by 2035 to support developing countries on the frontlines of the climate crisis.
The Local Leaders Forum will open with the C40 World Mayors Summit, highlighting two decades of progress by C40 Cities in advancing climate goals and improving daily life for urban residents. The Summit will spotlight priority actions for the next 12 months to stay on track and identify how to give cities the resources needed to meet the scale of the challenges ahead. Key themes will also include combating disinformation, tackling rising inequality, accelerating the transition from fossil fuels, and responding to the growing impacts of climate change.