We have more acronyms for your increased state of general confusion. The AR5 is coming up (Assessment Report 5) to be relapsed by the IPCC in 2013 (Intergovernmental Panel on Climate Change.) This generation’s report will look at newly created scenarios that more appropriately simulate atmospheric physics than the current scenarios. Scientists are leaving behind the somewhat policy based scenarios for the new batch that simply states trajectories and end, or the physical amount of greenhouse gases in our sky at a given point, rather than speculating on the 28 or so previous scenarios that looked at emissions and socioeconomic world evolution
This is good thing in that it allows for a better view of the science to be made. it is more simple and to the point. The CO2e level is easily measured and modeling related to the scenarios is more easily described than with the previous system.. These scenario families will no longer have the A1B, A1FI type of designations but will be more simple and more descriptive.
This new system is made up of RCP Scenarios (Representative Concentrations Pathways): RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5. They are more descriptive in that for example, the RCP 4.5 scenario projects for 4.5 w/m2 (watts per square meter) radiative forcing in 2100. The scenario’s 4.5 W/m2 means roughly 525 parts per million carbon dioxide in the atmosphere (currently, CO2 concentrations are climbing through 390 parts per million). Most importantly, 525 ppm CO2 corresponds to about 650 ppm CO2e. the little "e" stands for equivalent, or the equivalent greenhouse gas forcing in CO2 equivalents when all greenhouse gases are taken into consideration. CO2e includes, methane, ozone, and the myriad other greenhouse gases emitted by man.
RCP 2.6 2.6 w/m2 500 ppm CO2e The best case scenario: CO2e rises to 500 ppm before leveling off at 450 ppm Compares to the B1 Scenario CO2e of 640 ppm
RCP 4.5 4.5 w/ms CO2e rises to 525
RCP 8.5 8.5 w/m2 1464 CO2e Compares to A1FI Scenario at 1360 CO2e