The Intergovernmental Panel on Climate Change (IPCC) has laid out a range of scenarios for what might happen to the planet, atmosphere, biosphere, and human society over the course of the next century. These scenarios are based on different “Representative Concentration Pathways” (RCPs), each with its own story line about population growth, economic activity, land use patterns, energy use, lifestyle, climate policy, and mitigation efforts. RCPs provide time-dependent projections of atmospheric greenhouse gas (GHG) concentrations. Their purpose is to contribute to a better understanding of the uncertainties, interactions and dynamics involved in climate change and provide guidance to policy makers. In the IPCC Synthesis Report: Summary for Policymakers (2014), the authors compare four RCPs: RCP2.6, RCP4.5, RCP6.0, and RCP8.5. These four RCPs don’t exhaust all plausible trajectories but do cover a reasonable range of severity, from the pretty manageable to the horrific. At the pretty manageable end is RCP2.6, whichprojects that by 2100 the mean global temperature rise will be 1°C, with a likely increase range of 0.3 to 1.7°C. At the other end, RCP8.5 projects a mean temperature rise of 3.7°C and a likely increase range of 2.6 to 4.8°C.
The RCPs are only as good as their story lines - that is, what they choose to assume about humanity'snear-futurein order for their projections to be plausible. So, what are the assumptionsthat inform these Pathways?