More than half of the world’s population currently lives in cities, and by 2050, the UN estimates that figure will rise to nearly 7 in 10 people. The world is also getting hotter, with heatwaves and wildfires becoming increasingly common. So how can we deal with the dual challenges of increasing urbanisation and extreme weather caused by climate change? Perhaps we should look downwards. For millennia, humans have taken refuge underground from the elements, predators and from war. Even today, bomb shelters exist under major cities like Beijing and Seoul. Many cities across the world have subway systems for easy transportation – and some are integrated seamlessly with below-ground business and shopping centres. But what are the future challenges for urban planners and architects in this subterranean space, and how can we overcome the social stigma against those who live underground? This week on the Inquiry, we ask: is our future underground? Contributors: Martin Dixon, trustee of Subterranea Britannica, a society devoted to the study and investigation of man-made and man-used underground places. Jacques Besner, architect and urban planner; co-founder and general manager of Associated Research Centres for Urban Underground Spaces. Antonia Cornaro co-chair of ITACUS, the International Tunnelling and Underground Space Association's Committee on Underground Space. Professor Clara Irazábal, Director of the Urban Studies and Planning Program at the University of Maryland, USA. Presenter: Tanya Beckett Producer: Ravi Naik Editor: Tara McDermott Researcher: Matt Toulson Production Coordinators : Janet Staples & Liam Morrey Photo by BEHROUZ MEHRI via Getty Images