Sensitivity analysis of emissions corridors for the 21st century

We investigate the sensitivity of emissions corridors for the 21 century to various factors currently under debate in the climate change arena. Emissions corridors represent the range of admissible emissions futures that observe some predefined guardrails on the future development of the human-climate system. They are calculated on the conceptual and methodological basis of the tolerable windows approach. We assess the sensitivity of the corridors to the choice of time-resolved as well as intertemporally aggregated guardrails that exclude an intolerable amount of climate change on the one hand, and unbearable mitgation burdens on the other. In addition, we investigate the influence of climate sensitivity on the corridors. Results show a large dependence of emissions corridors on the choice of guardrails and the value of climate sensitivity T2CO2 . If the guardrail on climate change is specified in terms of a maximum admissible global mean temperature increase Tmax to be observed at any time, the size of the corridors is predominantly determined by a climate impact resilience parameter κ = Tmax/T2CO2 . As κ is varied from values below 0.5 to values above 1.5, we move from cases, where no emissions profile whatsoever can observe all guardrails, to cases, where no significant emissions reduction seems necessary given the range of emissions scenarios for the 21 century. The limits on admissible mitigation efforts influence predominantly the timing and the economic viability of emissions reductions. A large mitigation flexibility allows for ‘wait then run’ emissions paths, while low flexibility asks for a significantly more prudent approach.