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BAU Temperature, Emissions and CO2e Assumptions

Thank you to the entire ENROADS team for developing a terrific tool for modeling and teaching climate mitigation. It will be useful for helping students grapple with the need to change how we meet future energy demand. Now on to three items of interest/concern.


First, in the January 21, 2020 session, we discussed the BAU temperature anomaly for ENROADS RCP 8.5. The model assumes a BAU 4.1 C change by 2100, however the base of the anomaly - what it is calculated from - is unclear. The response to my query was that the model uses 1850 as the preindustrial global mean temperature base, but this is not clear in the ENROADS notes or sources. 


If the ENROADS temp anomaly is based on 1850, is this coming from the HadCRUT 4.6 annual data? If so, it states an global mean temperature anomaly of -.373 C for 1850, but the HadCRUT 4.6 anomaly base is the 1961-1990 global annual mean temperatures. This determination and explanation matters because there are different time periods and assumptions of preindustrial temperatures and emissions. For example, GISSTEMP uses 1951-1980. NOAA/NCEI Global Temp uses 1971-2000. They end up with different historical anomalies given differences in modeling and data sets.


Being clear about what the ENROADS anomaly base is helps establish credibility with its temperature assumptions and what they represent.


Second, in regard to emissions, the carbon cycle model builds from a preindustrial emissions base of 590 gigatons of emitted CO2. However, no source or definition of where that number comes from is available in the reference guide. It will help if that information is available since it is the foundation of future cumulative CO2 emissions in the carbon cycle model. 


Third, ENROADS graphs total CO2e emissions per year, and also greenhouse gas concentrations as CO2e ppm for each year to 2100. These are both helpful, but the CO2e may be under-reported. The NOAA ESRL AGGI CO2e is significantly higher for the historical past. 


For example, ENROADS has calculated a 451.3 ppm CO2e for 2018. The NOAA ESRL Annual Greenhouse Gas Index (AGGI) finds a 496 CO2e ppm for 2018. See: https://www.esrl.noaa.gov/gmd/aggi/aggi.html 


This total CO2e issue has an impact on the model temperature anomalies since it represents a 45 ppm CO2e variance between ENROADS and NOAA ESRL radiative forcing (Wm2) calculations. 


Thanks for all the presentations and work that goes into making ENROADS a  compelling tool to learn and use to encourage future energy system change.

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