C40 is a network of mayors of nearly 100 world-leading cities collaborating to deliver the urgent action needed right now to confront the climate crisis. Together, C40 can create a future where everyone, everywhere can thrive.

What they do today will determine whether or not there is a thriving future for communities, cities and the natural world around us. They know that climate breakdown and rising inequality, compounded by the COVID-19 pandemic, require an unprecedented response to match the scale of the crises. That’s why C40’s mission is to halve the emissions of its member cities within a decade, while improving equity, building resilience, and creating the conditions for everyone, everywhere to thrive.

C40 mayors have been at the forefront of climate leadership for over 15 years, driving the conversation around climate action and environmental justice to place these issues front and centre in their local policies and on the international agenda.

2005 – C40 is founded. Mayor of London Ken Livingstone convened representatives from 18 megacities to forge an agreement on cooperatively reducing climate pollution and created the ‘C20’.

As the elected leader of the C40 organisation, the Chair plays a key role in raising the bar on climate ambition around the world and advocating for the role of cities in addressing the climate crisis.

Mayor of London Sadiq Khan became C40 Chair in December 2021. In a keynote speech given during COP26 in Glasgow, Mayor Khan committed to align C40’s budget and staffing behind efforts to tackle air pollution worldwide and support emissions reduction strategies – particularly in Global South cities on the frontline of the climate crisis, putting social justice at the heart of his vision for C40 cities.