The SSP4: A World of Deepening Inequality

Researchers explored the consequences of a climate future that imposes high challenges to adaptation but low challenges to mitigation.

The Science

A recent study explores the implications of inequality on the evolution of energy, land, and climate.

The Impact

The Shared Socioeconomic Pathway 4, or SSP4, is part of a suite of scenarios designed to integrate climate change research over the coming decades to offer researchers an understanding of a climate future under a prescribed set of circumstances.


Researchers have developed five new scenarios, or Shared Socioeconomic Pathways (SSPs), spanning a range of challenges to mitigation and adaptation to climate change. These scenarios are designed to be used throughout the climate community, including the Coupled Model Intercomparison Project (CMIP) and Intergovernmental Panel on Climate Change (IPCC), facilitating integrated research on climate science, impacts, and mitigation. These scenarios were designed as part of a multiyear, multinational community effort.

SSP4, “Inequality” or “A Road Divided,” is one of these scenarios, characterized by low challenges to mitigation and high challenges to adaptation. Department of Energy researchers from Pacific Northwest National Laboratory, working at the Joint Global Change Research Institute describe, in quantitative terms, the SSP4 as implemented by the Global Change Assessment Model (GCAM), the marker model for this scenario. They used 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, and emissions consistent with the SSP4 narrative. The scenario is one with stark differences within and 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 economic growth. Growth in total consumption is dominated by increases in population, not increases in per capita consumption. Due to failures in energy access policies, these regions continue to depend on traditional biofuels, leading to high pollutant emissions. Declining dependence on fossil fuels in all regions means that total radiative forcing absent the inclusion of mitigation or impacts only reaches 6.4 W m-2 in 2100, making this a world with relatively low challenges to mitigation. The research explored the challenges of following more constrained Representative Concentration Pathways (RCP) pathways in an SSP4 world, finding that the imposition of economic signals to reduce emissions has varied effects across regions. In particular, the SSP4-RCP combination scenarios are characterized by afforestation in the high-income regions and deforestation in the low-income regions. Furthermore, the research shows that the SSP4 is a world with low challenges to emissions reductions, but only to a point, due to challenges in reducing land-related emissions.

Principal Investigator(s)

Katherine Calvin
Joint Global Change Research Institute, Pacific Northwest National Laboratory


This work was supported by the Department of Energy, Office of Science, Office of Biological and Environmental Research as part of the Integrated Assessment Research Program.


Calvin, K., et al. 2016. “The SSP4: A World of Deepening Inequality,” Global Environmental Change, DOI: 10.1016/j.gloenvcha.2016.06.010.
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