1.2 vs 1.3 Factor Change Drivers?

[ranastasiadis]

Hello, I hope you are well.

The document Aboutv1.3SupplyChainGHGEmissionFactors describes the comparison to the previous v1.2 factors, where the "median change in the CO2e SEFs was -18%" and "Of the 1016 Supply Chain Emission Factors with Margins, 139 increased by more than 5%, and 796 decreased by more than 5%."

Can you provide any possible reasons that would cause the majority of emission factors to decrease? We are trying to understand how much of the aggregate reduction in emission factors was an actual reduction in US emissions intensity (i.e., year-over-year reduction in total US emissions / total US GDP) vs driven by methodology changes from v1.2 to v.13 (e.g., the switch from AR4 to AR5).

Thank you!

[bl-young]

The v1.2 factors are based on 2019 GHG emissions, while v1.3 used 2022 GHG emissions. There are a number of nice time series figures here that show how emissions have changed over time, both in raw totals and per $ GDP. While those aren't directly comparable to the supply chain factors, we would expect similar directional change (i.e., decrease emission factors over time). I would expect that among other things, changes in the electricity sector would reduce supply chain emission factors across the board, all else being equal.

You can also use the pollutant specific factors to see what impact the change from AR4 to AR5 might have had.