The C40 Cities Climate Leadership Group (C40) is a network of the world’s megacities committed to addressing climate change.

Acting both locally and collaboratively, C40 Cities are having a meaningful global impact in reducing both greenhouse gas emissions and climate risks. C40 brings together a unique set of assets and creates a shared sense of purpose. C40 offers cities an effective forum where they can collaborate, share knowledge and drive meaningful, measurable and sustainable action on climate change.

Explore an interactive list of the C40 Cities and our Networks and Research connecting them.

C40 Cities: Showing the Way Forward

Take a ride with us through five of our cities to see actions and progress.

See the C40 like never before in this short video that takes you on a journey through member cities London, Johannesburg, Jakarta, Rio de Janeiro and New York. 

Meet the C40 Cities taking action.

C40 & Climate Week NYC 2014

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C40's message takes center stage in New York's Times Square during Climate Week 2014.

C40 Chair, Mayor of Rio de Janeiro, Eduardo Paes and all of C40 welcomed member cities and partners to Climate Week, which helped  demonstrate the growing demand for — and promise of — a global agreement on climate action. Learn more about C40's activity during this pivitol week including the C40 & Siemens City Climate Leadership Awards. The leadership role of cities has become clear -- and C40 recently released a series of new research findings and publications to inform that leadership, including the global Compact of Mayors and a special report from UN Secretary-General's Special Envoy for Cities and Climate Change and President of the C40 Board of Directors, Mayor Michael R. Bloomberg.