A new global coalition of cities has pledged urgent, coordinated action to tackle one of the most dangerous impacts of the climate crisis: extreme heat.

Announced on the first day of the C40 World Mayors Summit in Rio de Janeiro, the Cool Cities Accelerator will help urban leaders protect residents, safeguard economies, and redesign cities for a hotter future.

The initiative brings together 33 founding cities representing over 145 million people from every region of the world. This includes 5 cities in Africa: Accra (Ghana), Durban (Ethekwini – South Africa), Freetown (Sierra Leone)
Nairobi (Kenya), and Tshwane (South Africa).

C40 established the Accelerator with support from The Rockefeller Foundation, and with implementation support from ClimateWorks Foundation, Robert Wood Johnson Foundation, Z Zurich Foundation, Danish Ministry of Foreign Affairs, and IBM.

Extreme heat is already the deadliest weather-related hazard worldwide, responsible for nearly half a million deaths each year. Without decisive action, the number of people exposed to life-threatening urban heat is projected to increase fivefold by 2050. These 33 cities are committed to taking that decisive action.

The vast majority of deaths caused by extreme heat are preventable through timely access to cooling, hydration, medical care, public health interventions, and improved infrastructure. These preventable deaths typically occur when individuals—especially vulnerable populations such as the elderly, outdoor workers, or those without access to air conditioning—are not adequately protected during periods of dangerously high temperatures.

The Cool Cities Accelerator provides a science-based, practical framework for cities to take both immediate and long-term action.

Participating cities will collaborate, share best practices, and issue progress reports protecting residents now by establishing clear heat leadership, strengthening early warning systems, and ensuring access to cooling during emergencies within two years.

They will also look at transforming cities for the future by improving building standards, expanding urban tree cover and shade, and future-proofing critical infrastructure within five years.

"Extreme heat is no longer a distant threat—it's a daily reality affecting the lives and livelihoods of millions around the world," said Elizabeth Yee, Executive Vice President of The Rockefeller Foundation. "Through the Cool Cities Accelerator, we're proud to support mayors who are investing in bold, science-based solutions to future-proof health systems, ensuring they can withstand 21st century challenges. Local leaders are not just responding to the climate crisis today—they're redesigning urban life to protect people, strengthen economies, and build a cooler, safer future for all."

"Extreme heat is a silent killer and an increasingly urgent global threat," said Mark Watts, Executive Director of C40 Cities. "The number of days that major capitals experience temperatures above 35°C has increased 54% over the past twenty years. Cities are showing real leadership by taking practical steps to protect communities, safeguard economies, and create more liveable urban environments.

In support of the Cool Cities Accelerator, The Rockefeller Foundation is providing a grant of approximately USD 1 million to develop the targets for heat adaptation and provide technical assistance for cities to implement solutions that mitigate the dangerous effects of extreme heat.

The Cool Cities Accelerator is part of C40 Cities' broader mission to support bold, science-based climate action in the world's largest and most influential urban areas. By sharing strategies and scaling proven solutions, cities can act faster and more effectively than they could alone.

Together, participating cities represent a global movement to save lives, strengthen resilience, and create thriving, heat-resilient cities for generations to come.