Once a community’s overall sources and uses of energy are established, citizens and government officials must determine how to focus their emission-reduction efforts. To do so, they can use a carbon wedge analysis, an adaption of the wedge stabilization models that Princeton University economists led by Robert Socolow and Stephen Pacala developed in 2004, which have become a standard tool for breaking down carbon emission reduction targets.
As with the energy maps described in Part Two of this series, a carbon wedge analysis represents order-of-magnitude estimates based on best available local data and research assumptions and are intended to depict the broad scale of action needed to reduce carbon emissions.
To create the carbon wedge analysis, we first calculate the expected increase in carbon emissions—assuming no reduction efforts—based on the growth factor that a city or county planning office provides from the baseline which will be the year for which data were available to create the community’s energy map. This will create a line sloping up from the baseline and will reveal the greenhouse gas emissions that must be avoided.
Next, we apply the community’s carbon reduction target, often 50% of the baseline year’s emissions by 2030 or 80% of 1990 emissions by 2050, the target that many U.S. communities committed to prior to the Paris Agreement. This will create a line sloping downward and will indicate the greenhouse gas emissions that will need to be reduced.
Now you have the parameters of the wedge analysis established and can begin to carve up different reduction “wedges” based on existing policies and strategies, as well as on those that must be passed and implemented to achieve the desired target. Here is the beginning of the City of Shoreline’s wedge analysis:
City of Shoreline Starting Carbon Wedge Analysis
First, we look at the federal Corporate Average Fuel Economy standard, or “CAFE,” which requires that all new cars sold in the model year 2030 will have 54.5 miles per gallon. The Trump Administration has announced its promised rollback of these standards, and California and 18 other U.S. states promising to fight these proposals.
For the purposes of this exercise, we are assuming that the CAFE standards remain in place and that all cars on the road in 2050 would have at least that fuel economy. In the graphic of Shoreline’s Carbon Wedge Analysis below, this wedge is the Federal Fuel Economy Standard and is represented by the deep blue wedge at the top of the triangle.
Second, we looked at a state’s clean energy standard, in this case Washington State’s Renewable Portfolio Standard (RPS), which requires utilities to have renewable energy make up 15 percent of its fuel mix by 2020. In the case of Shoreline, the RPS is not relevant because Seattle City Light provides Shoreline’s electricity and it is 97% clean.
(Please see this compendium of eight cities in Washington and Oregon for whom we have created Energy Maps and Carbon Wedge analyses, where you can see how the RPS helps cities, such as Issaquah, WA or Kirkland, WA, meet their carbon emission reduction targets when their electricity is powered by coal and/or natural gas.)
Third, we looked at the Washington State Energy Code, which is one of the most stringent in the nation and requires new buildings constructed in 2031 to be 70 percent more energy efficient than those built to the 2006 energy code. In the Shoreline Wedge Analysis, the State Energy Code is orange.
These existing policies help get Shoreline to reduce its emissions to nearly its 2012 baseline, but to attain it 50% below 2012 emissions by 2030 target, Shoreline has to develop additional reduction targets for the built environment and especially in transportation, something that Shoreline’s Energy Map displayed in Part Two of this series made clear.
City of Shoreline Complete Carbon Wedge Analysis
The City of Shoreline’s planners and community members set three targets that if achieved would get them to their 50% below 2012 levels by 2030 goal, which can be seen on the wedge analysis as follows:
City of Shoreline 25% Cleaner Fuels & Vehicle Technologies
To attain Shoreline’s 25% cleaner fuels target, we modeled the impact of two strategies, a statewide clean fuels standard and a Community Clean Vehicle Partnership. Washington State does not have a clean fuels standard, while California and Oregon do. But if one were in place—and advocates continue to try to pass one in the Washington State Legislature—it would get Shoreline to 10 percent reduction in vehicle carbon intensity.
Shoreline looked at creating a community-wide clean vehicle market penetration strategy to make up the other 15% reduction required for cleaner fuels. This included deploying electric vehicle charging infrastructure; a more aggressive workplace charging and employee electric vehicle incentive program; and passing EV-ready building codes.
City of Shoreline 35% Vehicle Miles Traveled
Shoreline developed four additional transportation strategies to achieve the 35% reduction in vehicle miles traveled: congestion and parking pricing; land use planning and zoning reform, particularly in conjunction with transit-oriented development, housing choice surrounding its new light rail station; transportation demand management; and pedestrian, bicycle, and transit facilities and services, such as cycle tracks, bike share, electric vanpools, around the light rail station areas.
The vehicle miles traveled reduction strategies the city of Shoreline decided to pursue include:
While Shoreline’s clean electricity means that its planners do not have to concentrate efforts to decarbonize their electricity supply, natural gas provides power to many buildings in the area, hence the 40% reduction in natural gas in buildings by 2030.
City of Shoreline 40% Reduction in Natural Gas for Heating
To achieve this aggressive decrease in the use of natural gas, Shoreline must develop an energy efficiency program for retrofitting existing buildings, as well as strategies for employing renewable energy for heating. Here is where the city decided to concentrate their efforts:
With this analysis framework in place, the City of Shoreline has established a variety of pathways and strategies to attain its 50 x 2030 goal. Achieving these aggressive targets will require an ongoing commitment from elected leaders; creative partnerships; community support; state, regional, and local policy support; and funding. But the City of Shoreline is a leader in the nation in determining how to reduce its community's greenhouse gas emissions and is to be commended for its ambition and commitment to addressing climate change.
For further information regarding this subject, see the Clean Energy Transition Institute's presentations on City-Led Clean Energy Innovation, Urban Clean Energy Efforts, and City-Led Climate Action. Also see the City Climate Solutions References list.
Part One of a four-part series examining the role local jurisdictions can play in reducing carbon emissions: