“So-called street canyons in dense cities can create microclimates. Arrayed along rectilinear city grids, sets of skyscrapers can effectively increase wind speeds. Depending on their geometries, clusters can also raise temperatures by capturing solar energy or trapping warm air, thereby exacerbating existing urban heat island effects. In some cases, street canyons channel aerial pollutants up and out of the way—arguably a net benefit to the citizens below—but in other places, tall towers can collectively trap and recirculate smog in undesirable holding patterns.”