The previous article reported on the findings of a research study conducted at Monash University in relation to the completeness of a greenhouse gas assessments being conducted in Australia using a sample of twenty two organisations. The other four principles for a quality assessment outlined by The GHG Protocol are transparency, consistency, relevance and accuracy. This article will focus on the last of these, which was another theme of the same research.

Accuracy of a report results from a combination of the validity of activity data collected, and the emissions factors used to convert that level of activity into a mass of greenhouse gases. This research analysed the accuracy of conversion values applied through a comparison of emissions factors used for three commonly included sources of emissions: flights, paper and taxis.

Of the fifteen research participants who obtained an emissions factor and performed their own calculations, five different information sources were cited, resulting in an almost three-fold discrepancy in reported emissions for equivalent flights. Additionally, nine applied a radiative forcing index (RFI) multiplier and six did not, further exacerbating the discrepancy in emissions for equivalent flights.

Of the five known and cited sources for flight emissions factors, three repeated information from another source which had subsequently been updated. This reliance on outdated secondary sources thus caused a significant portion of the discrepancy, especially as many omitted the guidance on RFI contained in the original.

The actual RFI value to be applied is still the subject of scientific debate but there are no scientific articles which advocate there is no multiplier. Thus the practice of omitting an RFI multiplier altogether, due to the uncertainty as to the correct value or by omission, directly contradicts the principle of accuracy required for a quality emissions assessment.

Of nine respondents reporting taxi emissions, seven used a similar methodology to calculate their emissions, starting with dollars of expenditure as an activity measure. The effective kg CO2-e per dollar of taxi expenditure rates arrived at by these seven respondents ranged from a low of 0.1078 to a high of 0.2150. Whilst some variations in taxi fares exist between cities, this did not explain the full extent of the discrepancies. Some notable aberrations were identified in the choice of source data used by some respondents, particularly at the low end of this emission factor range. Principal among these was the use of nominal vehicle mileage values, rather than figures based on actual fuel consumption.

Five information sources were used by eleven participants reporting paper emissions calculated themselves after obtaining an emissions factor. The lowest conversion value used was 1.0 kgCO2-e per kg of paper and the highest a split value between virgin (1.867 kgCO2-e/kg) and recycled paper (1.907 kgCO2-e/kg). Only one of the five sources was cited by more than one respondent to this research – the values which were published by EPA Victoria.

Wide discrepancies in conversion values were in evidence. With the highest conversion factors for each of these sources being up to three times the value of the lowest, there was a material effect on the accuracy of total assessed emissions. Furthermore, in many cases a poor selection of emission factor had not been corrected during external audit processes. Of greater concern for both accuracy and completeness however, was that some respondents had chosen not to report at all on emissions sources where there was some uncertainty over the optimal emissions factor to apply.

Recommendations arising from this research are thus:
1. When selecting emission factors, wherever possible follow citation trails to the original source. In particular do not assume that second hand information, even in a publication from a reputable source, always necessarily contains all the necessary or the most recent information available.
2. Wherever possible, try to use values based on real use, rather than theoretical
3. Remember that the overall objective of a carbon footprint report is to represent your impact on global warming. Accordingly the choice of emission factors should be based on the best available science and representation of your organisations activity based on the best achievable data. Omitting sources due to questions of accuracy only further undermines the completeness of the picture presented in the report.

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3 Responses to Points to Remember for Accuracy in Calculating Scope 3 Emissions

  1. home health says:

    Keep posting stuff like this i really like it

  2. Great work keep it coming, best blog on earth

  3. Lars Lohmann says:

    Your comments and research are very useful. It also points out how difficult it is to still find reliable (transparent, consistent) Scope 3 emissions factors. While GHG Protocol is developing more rigourous Scope 3 emissions accounting, whatever factors are used will still only be global level emissions factors. There is a clear need for the Australian government to invest more in developing Scope 3 standards which companies can use – particularly for NCOS voluntary reporting. Hats off to the NZ Governement for publishing quite a few standards for Scope 3 emissions. If they can do so could Australia!

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