AI and other data-intensive technologies may help optimise energy use, but the technologies themselves are power hungry. This column explores how the diffusion of AI affected emissions in the US between 2002 and 2022 and finds that local AI growth raises emissions by boosting economic activity and energy use. It also leads to power generation becoming more carbon-intensive as plants shift from renewable to non-renewable sources. The ‘green’ promise of AI will remain elusive as long as the electricity sector itself does not rapidly decarbonise.