The leaked IPCC drafts are hard to read because they refer to a set of projections for greenhouse gas emissions pileups, and excess average radiation stored in the earth’s systems. These are called RCPs, or Representative Concentration Pathways. While the prase is accurate, I can’t easily remember it or what it stands for. Either greenhouse gas projections or radiative forcing futures would have been easier to remember and more meaningful, or even shorter corporate phrases like “scorched earth”s.
They are labeled by their radiative forcings in Watts per square meter (W/m^2) in the year 2100. Except for the most optimistic, the RCP3, where the peak of 3 W/m^2 is reached mid century and actually declines after that. The worst one is “business as usual” with no attempts to limit greenhouse gases, which is RCP8.5, which ends the century at 8.5 W/m^2. The present radiative forcing or increased radiation absorbed by earth systems since preindustrial times has been increased to 2.4 W/m^2 in IPCC 5.
Here is a graph of the radiative forcing pathways for the RCPs:
The IPCC uses IMAGE 2.6 for 2.6 W/m^2 peak at the lowest, and the emissions pathways are also shown below:
The maximum forcing path RCP 8.5, has over three times the emissions and over three times the radiative forcings as at present.
