Four of the world’s largest cities announced Friday that they will ban diesel cars by 2025 in an effort to cut air pollution.Leaders from Paris, Madrid, Athens, and Mexico City made the declaration at the C40 Mayors Summit, a biennial meeting of civic leaders concerned about climate change. Toxic air is responsible for an estimated 3 million premature deaths each year, according to recent research by the World Health Organization. While diesel engines burn fuel more efficiently and therefore release less carbon dioxide, they do produce nitrogen dioxide and particulates that can inflame and damage people’s lungs. “Mayors have already stood up to say that climate change is one of the greatest challenges we face,” said Anne Hidalgo, the mayor of Paris. “Today, we also stand up to say we no longer tolerate air pollution and the health problems and deaths it causes.”