2C or not 2C?

Political attention has increasingly focused on limiting warming to 2 °C. However, there is no consensus on both questions “Is the 2 °C target achievable?” and “What should be done with this target that becomes increasingly difficult to achieve?”. This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2 °C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an “uncertainties and decisions tree”, linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change. ⺠The paper proposes simple visualizations of the challenge posed by the 2 °C target. ⺠It shows how key assumptions influence the achievability of the target. ⺠It disentangles the points of deep uncertainty underlying the absence on consensus on the achievability of the target. ⺠It proposes an “uncertainties and decisions tree”, linking different beliefs on climate change to various policy options.