SI 1. Impulse response of the carbon cycle
In figure SI 1 we compare the impulse response to a pulse emissions of CO2 in DICE 2016 2R to the pulse response used for calcluating Global Warming Potentials (GWP) in IPCC AR5 (Myhre et al, 2013). The Impule response used in IPCC AR5 chacterizes the impulse response close to present days concentrations and is the basis for the carbon cycle in the FAIR model. As can be seen in the figure, a substantially larger fraction of a CO2 pulse emission stays in the atmosphere for the carbon cycle in DICE 2016 R2 than in the carbon cycle in IPCC AR5. However, it must be kept in mind that the carbon cycle is non-linear and the removal rate decreases with increasing atmospheric concentrations (which is considered in the revised carbon cycle, but not in DICE-2016R2). The impulse response in DICE-2016R2 is likely to be representable for far higher concentration than those compatible with keeping the global mean surface temperature at or below 2.5 °C above the pre-industrial level.