Sunnyvale staff say 2024 inventory spike driven by modeling and supplier issues; outline electrification, waste and data actions

City of Sunnyvale staff told the Sustainability Commission that the city's 2024 greenhouse gas inventory shows higher emissions than expected but that much of the increase is driven by changes in state models and a temporary change in the electricity supply mix, not by a sudden surge in local activity.

The inventory, which measures emissions relative to 1990 levels and supports the city's Game Plan 2028 target of 56% below 1990 by 2030, showed large increases in the transportation and electricity sectors for 2024. Staff said those increases reflect two main drivers: an updated California Air Resources Board (CARB) modeling assumption that reduced fleet fuel-efficiency inputs, and a short-term change in Silicon Valley Clean Energy's (SVCE) power purchases that increased emissions factors for electricity in 2024.

City staff emphasized the differences between model outputs and on-the-ground programs and listed recent and planned actions intended to reduce local emissions and increase resilience. They also described steps the city will take to clarify measurements and improve future reporting.

Staff's explanation and context

Presenters told commissioners the CARB model update lowered assumed fuel efficiency for gasoline and diesel vehicles (staff reported an example change from roughly 24 mpg to about 20 mpg for gasoline cars in the underlying county fuel-use data), which increased the calculated fuel use when that efficiency was applied to Sunnyvale's vehicle-miles-traveled (VMT) inputs. Staff described a 17% increase in transportation-sector emissions in the 2024 inventory driven by that modeling change and said…