All equations and parameters in En-ROADS are included in the ~400 page Reference Guide. Some of the key assumptions are listed below.


For the En-ROADS Business as Usual (BAU) scenario, we chose to adopt the baseline scenario definition from one of the foundational papers on the Shared Socioeconomic Pathway scenarios, (Riahi et al., 2017): “a description of future developments in absence of new climate policies beyond those in place today” and which “do[es] not consider feedbacks from the climate system on its key drivers such as socioeconomic impacts of climate change.”


Assumptions behind drivers of growth in CO2 emissions:

The drivers of growth in carbon dioxide emissions are explained by the Kaya equation

Global Population x GDP per Capita x Energy Intensity of GDP x Carbon Intensity of Energy = CO2 Emissions from Energy


  • Population growth: United Nations medium growth scenario

  • Economic growth (GDP per capita): 2.5% per year, slowing over time

  • Energy intensity of GDP

    • Buildings and Industry: 1.2%/year improvement in energy efficiency

    • Transportation: 0.5%/year improvement in energy efficiency

  • Carbon intensity of energy

    • Progress ratio for growth of renewables and new technology: 0.8 (every doubling of cumulative capacity brings a 20% drop in cost)


Other key assumptions in the En-ROADS BAU:

  • Methane: closely follows SSP2

  • Carbon removal: none

  • Climate system sensitivity (how much global temperature will increase per doubling of atmospheric CO₂ above pre-industrial levels): 3°C

  • Calibration: SSP2 baseline scenarios of a suite of Integrated Assessment Models, specifically, PBL IMAGE, PNNL GCAM4, PIK REMIND-MAGPIE, NIES AIM/CGE, IIASA MESSAGE-GLOBIOM, and EIEE WITCH-GLOBIOM (Riahi et al., 2017Rogelj et al., 2018Gidden et al., 2019)


Currently, the factors below are not included in the En-ROADS Business as Usual scenario:

  • Climate impacts such as negative economic repercussions of unmitigated climate change

  • Countries’ Nationally Determined Contributions (NDCs) under the Paris Agreement

  • Other future climate policy and associated economic impacts


You can modify many of these assumptions in En-ROADS in the Assumptions menu (under Simulation > Assumptions). Changing these assumptions will affect the current scenario but will not change the Business as Usual scenario (the black line in the graphs). You cannot modify the Business as Usual scenario in En-ROADS at this time.