Borders are back with a vengeance. From the Americas to the Mediterranean, borders cut through the increasingly integrated world in a way that exposes the inside-outside logic of contemporary capitalism. All this happens on a backdrop where cities are becoming the key sites of contestation since borders and levees do not suffice to keep them intact. Cities are also increasingly becoming the focus of international efforts to deal with climate change and migration, where nationstates are falling short. By synthesizing the possibilities of urban belonging and right-to-the-world, we argue that new urban imaginaries are at the frontline of the mobilities debate today. Consequently, we argue for a cross-pollination of mobility justice and climate justice as urban citizenship. The main thrust of our argument is that there are viable alternatives to the isolationist fortress nation model, which can bring a new dimension to debates concerning climate change and migration. Fearless cities are but one example of these emerging alternatives. By focusing on the opportunities for a radical response to climate change and migration, we suggest that cities can respond to the burning mobility challenges of our times with a just, grounded and egalitarian urban citizenship framed as mobile commons.