PNNL

Abstract

The Shared Socioeconomic Pathway 4 (SSP4), “Inequality” or “A Road Divided,” is one of the five SSPs developed to guide the creation of new scenarios for the “Parallel Process”. We describe, in quantitative terms, the SSP4 as implemented by the Global Change Assessment Model (GCAM), the marker model for this scenario. We use demographic and economic assumptions, in combination with technology and non-climate policy assumptions to develop a quantitative representation of energy, land-use and land-cover that are consistent with the SSP4 storyline. The resulting scenario is one with stark differences across regions. High-income regions prosper, continuing to increase their demand for energy and food. Electrification increases in these regions, with the increased generation being met by nuclear and renewables. Low-income regions, however, stagnate due to limited growth in income. These regions continue to depend on traditional biofuels, leading to high pollutant emissions. Due to a declining dependence on fossil fuels in all regions, total radiative forcing only reaches 6.4 Wm-2 in 2100, making this a world with relatively low challenges to mitigation. We explore the effects of mitigation effort on the SSP4 world, finding that the imposition of a carbon price has a varied effect across regions. In particular, the SSP4 mitigation scenarios are characterized by afforestation in the high-income regions and deforestation in the low-income regions. Finally, we compare the GCAM SSP4 results to other integrated assessment model (IAM) quantifications of the SSP4 and to other SSPs, both those generated by GCAM and those of the other IAMs.