The European Union is implementing a groundbreaking new tax: a carbon border tax. It's meant to prevent distortions between countries with differing emissions standards and so to reduce emissions. But will it work? The same can be asked about the International Maritime Organisation's proposed new carbon levy on shipping. Also on the show, an update on the Great Green Wall — China's mass-tree-planting project; and measuring stress in trees to improve resilience. Guests Associate Professor Anna Trugman — Department of Geography, University of California, Santa Barbara Honorary Professor Peter Bridgewater — Centre for Heritage and Museum Studies, Australian National University Professor Michael Brear — Director, Melbourne Energy Institute, University of Melbourne Dr Sanjay Patnaik — Director, Center on Regulation and Markets, Brookings Institute