What is Driving Changes in Local GHG Emissions?: Results from contribution analysis presents results from applying a new technique called Contribution Analysis to local community greenhouse gas (GHG) inventory data. Contribution Analysis separates out the impact of different drivers of change between multiple inventory years. The drivers looked at include population/ commercial growth, energy usage per person, and the carbon intensity of energy sources. Contribution Analysis is applied to three sets of GHG inventory data:
- Data from fifteen pilot communities where a detailed Contribution Analysis was completed, including the impact of weather on energy use.
- A broader data set of GHG inventories from 138 local governments.
- Sixteen years of annual data for one city, Portland, Oregon.
For each data set, emissions from residential and commercial electricity and from on-road gasoline use were analyzed. In addition, for the fifteen pilot communities, results are shown for residential and commercial heating fuels.
The key findings from this analysis are:
- Both a cleaner electric grid and energy efficiency have important roles to play to offset growth and reduce emissions from commercial and residential electricity. State-level policies advancing renewable energy, combined with local, utility, business and individual action for energy efficiency can overcome growth and drive significant emissions reductions.
- State energy efficiency policies have a noticeable effect on changes in commercial energy usage. Local governments in states with a high energy efficiency policy score show per-employee energy use decreasing more rapidly than those in lower-scoring states. This relationship was not found for residential energy use; more research is needed to determine why not.
- Both more efficient vehicles and reduced vehicle miles per person have important roles to play to offset growth and reduce emissions from on-road transportation. In a majority of communities analyzed, improvements in vehicle fuel efficiency and reductions in vehicle miles per person are sufficient together to reduce emissions despite population growth.
- Transportation emissions are more challenging than electricity emissions and more work is needed. While the overall trend is in the right direction, transportation emissions are not decreasing as rapidly as those from electricity, and emissions are still increasing for 37% of communities. More work is needed to address both vehicle miles per person and vehicle fuel efficiency or fuel switching.