A coalition of 40 mayors from cities spanning four continents has signed a landmark agreement establishing common standards for the construction of AI data centres, which city leaders say are straining power grids, consuming vast quantities of water and competing with housing for available land. Launched on Tuesday during London Climate Action Week by C40 Cities (an alliance of nearly 100 cities focused on tackling climate change), the pact calls for data centres to be built on underused land, powered by renewable energy, and required to reduce water consumption, cut emissions and create local jobs. The initiative — the first coordinated global effort by city governments to manage data centre expansion — was partly sparked by exchanges between the mayors of Phoenix and Melbourne, who discovered their cities faced near-identical pressures; pending permit requests in Phoenix alone could double the city's electricity demand, while Melbourne's current development plans could see data centres consuming up to 20 billion litres of water annually, roughly 4% of the city's drinking supply. About half of the 40 signatories are US cities, including Seattle, Chicago and Miami, with further signatories from Europe, Africa, India, Australia and Lebanon, though no Southeast Asian cities joined despite the region accounting for a quarter of global energy demand growth. Organisers warned that without a unified front, technology companies would simply move to cities with fewer demands.