The amount of future warming is predicated on the amount of emitted greenhouse gases and the sensitivity of earth’s surface temperature to changes in their concentrations. Here we take a look at the emissions component.
The U.N. currently entertains four emissions scenarios, all expressed as the change in downwelling radiation (in watts/meter-sq, nominal year 2100) towards the surface that results from an increase in the atmospheric concentration of certain greenhouse gases. They are called “representative concentration pathways,” or RCPs.
As can be seen in Figure 1, there are four, given as 2.6, 4.5, 6(.0) and 8.5. The ranges of associated warming for over 1000 total scenarios are given on the right axis.
Figure 1. Approximately 1000 scenario runs for four RCPs. From Fuss et al., 2014.