The C40 Cities Climate Leadership Group (C40) is a network of large and engaged cities from around the world.

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  • C40 is committed to implementing meaningful and sustainable climate-related actions locally that will help address climate change globally.

    Our global field staff works with city governments, supported by our technical experts across a range of program areas. Together we facilitate active exchange and collaboration across our cities.

Learn about our history and accomplishments.

Strong advocates for the role of cities in addressing climate change.

C40 was created in 2005 by former Mayor of London Ken Livingstone, and forged a partnership in 2006 with the Cities Program of President Clinton’s Climate Initiative (CCI) to reduce carbon emissions and increase energy efficiency in large cities across the world. Under the leadership of then Mayor of Toronto David Miller, who served after Mayor Livingstone as C40 Chair, the organisation advanced programs and partnerships that drew international recognition for the role of cities as leaders in climate action.

108th Mayor of New York City Mayor Michael R. Bloomberg served as C40 Chair from November 2010 to December 2013, during which time C40 fully integrated with the Clinton Foundation's CCI Cities Program. Mayor Bloomberg currently serves as President of the C40 Board of Directors.

Rio de Janeiro Mayor Eduardo Paes began his tenure as C40 Chair in December 2013.

Learn more about the people leading the organisation as part of the steering committee, Board of Directors, and management team.