Committee asks SSG to reconcile greenhouse gas inventory differences between 2020 baseline and 2023 results

Charleston County staff and committee members spent a substantive portion of the meeting reviewing greenhouse gas inventory results and methodological discrepancies between a 2020 baseline and a 2023 inventory produced by contractor SSG.

Speaker 7 said the committee received SSG’s 2023 inventory, but that it used a broader regional modeling approach that can yield different totals from the county’s earlier, localized baseline. "The 2020 inventory is what you'll see in our current sustainability plan, so that is our baseline," staff said, adding that SSG’s modeling includes larger-scale sources such as ports and regional transport.

Committee members asked whether specific sources — notably the airport — were included in the two different runs. Speaker 3 raised that question directly: "Did they include the airport per night? And are they now including the airport in the 2023?" He also flagged that the discrepancy between earlier county calculations and SSG’s results could be in the millions of metric tons of CO2 equivalent, and urged reconciling scope differences before adopting a new baseline.

Staff said they have arranged conversations between SSG and previous coordinators; SSG was asked to produce a more comparable, localized version in the new year so the county can agree on a consistent baseline prior to setting progress metrics. The committee noted its two largest emitter categories in the 2023 inventory appear to be industrial and transportation and stressed the importance of clarifying scope so local mitigation efforts are targeted appropriately.

Next steps: SSG will be asked to reconcile modeling choices and provide a comparable dataset early next year; the committee plans follow-up discussion once the reconciled inventory is available.