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Three hundred mayors from major world cities gathered in Rio de Janeiro to pledge coordinated climate action days before the U.N. conference.

Extreme heat kills nearly half a million people yearly and threatens $2.4 trillion in lost productivity by 2030, experts warn.

Fifty U.S. cities including Phoenix remain committed to climate action through the Cool Cities Accelerator, defying national policy rollbacks.

SAO PAULO — Just days ahead of the U.N. climate conference to be held in Brazil, a group of 300 mayors gathered in Rio de Janeiro to pledge coordinated climate action and address rising heat that is hurting many of their residents.

The summit Monday was organized by C40, a

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