Key points:

  • The En-ROADS Business as Usual (BAU) baseline scenario is not our prediction of the future. It’s a reasonable starting point for experimentation.

  • The En-ROADS BAU scenario is calibrated to the SSP2 baselines of six Integrated Assessment Models (IAMs).

  • The En-ROADS BAU scenario falls in the middle of the middle-of-the-road scenarios.

  • The En-ROADS BAU scenario is not calibrated to RCP 8.5. It is significantly lower than RCP 8.5.


The En-ROADS BAU scenario is not our prediction of the future. It’s a reasonable starting point for experimentation. In other words, it’s a control group: what would the world look like if we don’t take action on climate change and temperature continues to rise unabated? Then, how are the outcomes different if we take action? 


For more information about how we constructed the En-ROADS BAU, read this FAQ on “What is the background and meaning of your ‘Business as Usual’ scenario?”


There’s a lot of debate about what a Business as Usual (BAU) scenario should be. For instance, many people have come to refer to RCP 8.5 as the BAU scenario. Zeke Hausfather and Glen Peters have said this characterization is incorrect, while on the other hand a recent study by Woods Hole Research Center argues that RCP 8.5 is consistent with near- and medium-term emissions trajectories. The future emissions trajectory of the world is unknown, and we can only try to make informed guesses based on historical and current trends. 


The En-ROADS BAU scenario is calibrated to the SSP2 baselines of six Integrated Assessment Models (IAMs). The Shared Socioeconomic Pathways (SSPs) describe a large range of scenarios, such as high economic growth, low economic growth, heavy reliance on fossil fuels, etc. SSP2 is referred to as the “middle of the road,” a scenario of medium challenges to mitigation and adaptation. 


The En-ROADS BAU scenario falls in the middle of the middle-of-the-road scenarios. The graph below compares the En-ROADS BAU (solid blue line) to the baselines of six major Integrated Assessment Models (IAMs) for the SSPs: 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). The solid blue line of the En-ROADS BAU falls in the middle of the range of SSP baselines, as well as in the middle of the “middle of the road” SSP2 baselines (in purple, in both the first and second graphs). 





The En-ROADS BAU scenario is not calibrated to RCP 8.5. It is significantly lower than RCP 8.5. The graph below compares temperature change in the En-ROADS BAU scenario (the dark blue line) to six IAM baseline scenarios, as well as RCP 8.5 and RCP 6.0. The temperature change in the En-ROADS BAU scenario is lower than RCP 8.5 (the orange line) and higher than RCP 6.0 (the brown line), and falls in the middle of the spread of the IAM baseline scenarios for SSP2. 




One major component of more extreme Business as Usual scenarios that Zeke Hausfather and Glen Peters explained in their criticism of RCP 8.5 is the heavy reliance of that scenario on growth in coal primary energy demand. In the case of RCP 8.5, they cite an estimate that coal use would have to grow to five times its current demand by 2100, in gigajoules per capita (Ritchie & Dowlatabadi, 2017). The En-ROADS BAU primary energy demand of coal is very different. Primary energy demand of coal in gigajoules per capita in the En-ROADS BAU scenario grows to twice its current demand by 2100, far from the five-fold increase of RCP 8.5. The chart below shows the change in coal in GJ/capita between 2020 and 2100 in the En-ROADS BAU. This is in line with the change in coal primary energy demand in the SSP2 baseline of other models, as we explain in our FAQ on coal in En-ROADS



Year

En-ROADS BAU Coal GJ/year

En-ROADS BAU Population

En-ROADS BAU Coal GJ/capita

2020

1.69E+11

7.79E+09

21.69

2100

4.553E+11

1.09E+10

41.89

*GJ = gigajoules. 1 exajoule = 10^9 gigajoules


We are watching the latest research and discussion about BAU scenarios and may update En-ROADS in the future to reflect a new consensus in the field. We are also in the process of exploring the option to model alternate BAU scenarios in En-ROADS.