At Copenhagen in December 2009, the international community agreed to limit global warming to below two degrees Celsius to avoid the worst impacts of human-induced climate change. However climate scientists agree that current national emissions targets collectively will still not achieve this goal. Instead, the ‘ambition gap’ between climate science and climate policy is likely to lead to average global warming of around four degrees Celsius by or before 2100. If a ‘Four Degree World’ is the de facto goal of policy, we urgently need to understand what this world might look like.