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Cities as Climate Labs: Inside the U20 Summit

Mayors at the Urban 20 Summit worked across borders to confront the climate crisis at the local level.

Amid tumultuous global politics and pervasive climate catastrophe, mayors from around the world have a clear message: Cities are taking up the mantle of climate action and international cooperation, regardless of whether their national governments choose to do so.

From intensified rains and flash flooding in New York City to fatally hot temperatures in Paris, cities are often on the front lines of climate change. In recognition that metropolitan areas are both uniquely vulnerable to these impacts and crucial laboratories for innovative solutions, climate was a core theme at the 2026 Urban 20 Summit (U20) cohosted by Los Angeles and New York City from September 19 to 21.

The Summit, organized by C40 Cities and United Cities and Local Governments, brought together mayors and senior leaders from more than 30 cities to discuss the pressing and deeply interconnected challenges of climate change, migration, and housing. The Summit occurred on the heels of High-Level Week at the United Nations and Climate Week NYC, both of which will see national governments discuss the future of climate action in a world already surpassing the 1.5-degree warming limit enshrined in the Paris Agreement.

With the shadow of these upcoming national government dialogues looming, mayors and city leaders made clear that climate action remains a priority for local leaders, and that tackling the climate crisis cannot be done in isolation from other interconnected social issues or without international cooperation.

Their unity and commitment represented a sharp contrast to the nationalist, xenophobic, and anti-science rhetoric of a surging far-right politics. Under the right-wing Trump administration, the US has withdrawn for the second time from the leading global climate treaty, the Paris Agreement, and undertaken a seismic environmental deregulation. Climate skepticism has also become a staple of right-wing parties in the United Kingdom and Europe. Meanwhile, New Zealand recently passed a law shielding fossil fuel polluters and the government from climate liability.

Yet, in a powerful display of global solidarity, the Summit made........

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