Charge €30 a tonne for CO2 to avoid catastrophic 4C warming | Ottmar Edenhofer and Johan Rockström

New global policies such as carbon pricing are needed if we are to avoid an apocalyptic increase in temperature

We are following a path that will ultimately take us to a 4C-warmer world. A hot state where it is unlikely that we can generate food, water and shelter for all citizens, where sea level rise will ultimately exceed 10 metres, and where social insecurity and widespread disease will very likely be universal.

Along the way we will reach several critical tipping points. One such is at 2C - a scenario that may prompt the Earth system to shift from self-cooling by means of buffering emissions to self-warming, thereby putting us on a path to a "hothouse Earth". At 3C we reach a point where extreme floods and droughts will force people to leave their homes; more powerful hurricanes will destroy urban infrastructure.