A global network of nearly 100 world-leading cities that are #UnitedInAction to confront the climate crisis and create a future where everyone can thrive. A global network of nearly 100 mayors #UnitedInAction to confront the climate crisis. Created by cities for cities, C40 advances climate action agendas of the world’s megacities to achieve meaningful reductions of greenhouse gas emissions and climate risk. C40 is a global network of engaged megacity mayors committed to reducing their greenhouse gas emissions and climate risk through the implementation of measurable, replicable and sustainable climate-related policies and programs. As a network, C40 equips and empowers cities to lead the fight against climate change while building the case for the global importance of climate action in growing city economies, creating jobs, and improving cities as places to live and work.