Boston's carbon emissions
Economic and Population Growth
The reduction in Boston’s emissions has occurred at the same time that the population and the number of jobs in Boston have increased. The Boston community has grown from 520 thousand residents in 2015 to more than 694 thousand in 2019. Emissions per resident over the same time period have decreased 41%, from 15 to 9 metric tons per year. Boston’s economic growth, as measured by Gross City Product (GCP), has increased from 106 billion dollars to 135 billion. Emissions per million dollars of GCP have decreased 39%, from 76 to 46 metric tons per million dollars.
Community-wide emissionsCommunity emissions
In his 2017 State of the City address, Mayor Martin J. Walsh announced the City’s goal of carbon neutrality by 2050. This commitment underlies the City’s Climate Action Plan, soon to undergo its third update. To measure progress, Boston follows the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC). The baseline year is 2005, the first year in which consistent and reliable data was collected. Boston has an interim goal to reduce citywide emissions by 25% by 2020.
The annual greenhouse gas inventory is based on a combination of direct data and estimates for data that cannot be obtained directly. Data sources include City records, utility company reports, and information from state and federal agencies. Reporting is separated into community-wide and local government operations inventories. Because the data for these inventories is collected using separate protocols on separate timescales, the Local Government Operations Inventory should be considered to be overlapping, but not completely contained within the Community Inventory.
The goal of the community inventory is to include GHG emissions associated with all activities — residential, commercial/industrial, institutional, transportation-related — within the administrative boundary of the City of Boston. The Boston community-wide inventory accounts for emissions from the following sources:
- Stationary energy use from residents, businesses and other activities, including municipal buildings.
- On-road and off-road transportation, including municipal vehicle fleet fuel use (airplane travel at Logan airport excluded).
- Solid waste and wastewater disposal and treatment.
In Boston, energy use in stationary sources dominates, accounting for 69% of total emissions (4.3 MtCO2e). Commercial, industrial, and large residential buildings generated 51% of emissions (3.1 MtCO2e), while small residential buildings accounted for 19% of emissions (1.1 MtCO2e). Fugitive gas emissions for all sectors account for less than 1% (30 thousand tCO2e) of emissions. Emissions in the building sector stem from the use of electricity (46%), natural gas (or methane gas) (45%), fuel oil (8%), and steam (2%).
Individual buildings over 35,000 square feet publicly report their energy and water usage annually. The data is available at: Analyze Boston.
- Commercial, industrial and large residential buildings, including high-rise offices, hospitals, universities and research buildings, manufacturing, and construction
- Small residential buildings
- Fugitive emissions from oil and natural gas (or methane gas) systems
Emissions from transportation comprise 30% of the inventory (1.9 MtCO2e). This is lower than transportation’s share of statewide or national emissions because of Boston’s density and robust public transportation system. More than half of Bostonians get to work via a mode other than a car (Go Boston 2030).
The inventory captures the emissions from the estimated Vehicle Miles Traveled (VMT) inside the City, plus public transportation and off-road vehicles used at the airport and wastewater treatment plant. Primary energy sources include gasoline (76%), diesel (20%), natural gas (or methane gas) (1%), electricity (2%), biodiesel and propane combined (<1%).
GHGs reported in the waste sector refer to emissions from wastewater treatment only and account for less than 1% of total emissions (18 thousand tCO2e). All, or almost all, of Boston’s solid waste is sent to Waste To Energy (WTE) incineration plants that feed the electricity grid, so emissions are counted as part of regional electricity generation. Boston has a Zero Waste initiative and the indirect accounting of emissions from solid waste in our GHG inventory does not affect the City’s commitment to waste reduction.
The Carbon Free Boston analysis estimated that Boston’s waste sector accounted 393 thousand tons of direct carbon emissions in 2017, if the WTE emissions are broken out from the electricity emissions factor. The Zero Waste Boston initiative has issued strategies to reduce, reuse, recycle and compost at least 80 to 90 percent of Boston’s solid waste. The Carbon Free Boston analysis determined that a 90 percent diversion rate would reduce waste emissions by 78% relative to 2017 emissions, including the WTE emissions.
In 2019, the community’s GHG emissions decreased nearly 2% (174 thousand tCO2e) from the previous year. This decrease reflects that:
- Regional emissions per unit of electricity decreased by 3.4%.
- Boston businesses and institutions consumed less electricity and Boston residents used less fuel oil.
- However, Boston residents, businesses and institutions used 2% less natural gas (or methane gas) than in 2018. The 2019-20 winter was slightly warmer than the 2018-19 winter.
Boston’s GHG emissions from 2005 to 2019 have declined by 21%. 51% of GHG reductions are the result of state-level and regional action to clean the New England electric grid. As a result, the electricity emissions factor has improved continuously over time, as electricity has been less carbon-intensive. Another 25% of GHG reductions may be attributed to reduced fuel oil use. This is because many households and businesses are switching from fuel oil to natural gas (or methane gas) to heat their homes. Steam has become cleaner thanks to fuel-switching from oil to natural gas (or methane gas) and the addition of the Kendall cogeneration plant in 2014. The average fuel economy of vehicles registered in Boston has also improved from 19.8 miles per gallon (mpg) in 2009 to 21.2 mpg in 2014 (most recent year for which Boston-specific data is available).
The inventory employs measured data, projections, models, and, where data is scarce, best estimates. All of these sources have some level of uncertainty, most of which have not been quantified. Furthermore, the inventory is frequently revised as new and better data become available, models are improved, new methodology is developed, and international standards evolve. For these reasons, longer term trends are likely more reliable than absolute numbers or year-to-year changes.
Municipal emissionsMunicipal emissions
The Local Government Operations (LGO) inventory calculates all greenhouse gas emissions generated by municipal operations in the City of Boston. This includes the burning of fuels in the City’s facilities, vehicles, and other equipment, and the energy used in municipal buildings, vehicles, parks, street lights, and traffic signals. The LGO inventory is based on the ICLEI greenhouse gas reporting protocol for local government operations.
Under the protocol, emissions that are not under the operational control of the City government or involve leased properties are excluded. Emissions from the Boston Housing Authority, the Massachusetts Water Resources Authority (MWRA), and the Boston Planning and Development Agency (BPDA) are not included in the inventory. Those from the Boston Public Health Commission (BPHC) and the Boston Water and Sewer Commission (BWSC) are.
While the timeframe for the citywide inventory is the calendar year, the LGO inventory is conducted on the fiscal year, from July to June. Because the data for these inventories is collected using separate protocols and on different timescales, the LGO should be considered to be largely overlapping but not completely contained within the Citywide inventory.
FY19 municipal emissions are down nearly 33% from 2005, before including adjustments for the purchase of renewable energy credits. Adjusting for the City of Boston’s purchases of Green-E Certified Renewable Energy Certificates (RECs) equal to approximately one fourth of our total electricity consumption, emissions in FY19 are down more than 40% from 2005 levels. The City of Boston met its municipal 2020 goal of a 25% reduction 5 years ahead of schedule.
Boston’s LGO emissions are dominated by building energy consumption. Electricity and natural gas (or methane gas) consumption by buildings each make up about one third of total GHG emissions. Transportation fuels, diesel and gasoline, together make up one fourth of total municipal GHG emissions.
Similar to the community-wide inventory, Boston’s municipal operations GHG inventory trends are driven by a number of external and internal factors. Diesel consumption is continuing to decrease as Boston Public Schools switches its fleets from diesel- to propane-powered school buses. The continued downward trend in the regional electric grid emissions rate also contributed to reduced emissions.
As the department with the largest building portfolio and the second largest vehicle inventory (after Boston Police Department), Boston Public Schools (BPS) represent the largest source of municipal emissions. BPS owns and operates approximately 11 million of the City’s 16.5 million square feet of building space across the roughly 127 school buildings in the district. These buildings represent over a third of municipal electricity consumption and two thirds of municipal natural gas (or methane gas) consumption.
The BPS Department of Transportation (DOT) fleet includes over 700 school buses and uses 73% of all the diesel fuel consumed by municipal government. BPS has continued their replacement of the oldest, dirtiest diesel buses to lower emissions propane engines; propane buses represented more than half of the fleet in 2020. Since BPS-DOT is on a roughly 10 year replacement cycle, these lower emissions vehicles will provide emissions reductions over the next decade.
The next largest source of GHG emissions from municipal operations is the Boston Police Department (BPD) at about 10.2% of total municipal emissions. In FY19, BPD operated approximately 660,000 square feet of building area and managed a fleet of over 1,000 vehicles. These buildings accounted for 7% of electricity and 5% of natural gas (or methane gas) consumed by City of Boston departments. The BPD fleet accounted for roughly 63% of all gasoline consumed by City of Boston vehicles in FY19.
The third largest source of GHG emission from municipal operation is the Public Works Department’s street lighting inventory. The 66,000 electric street lights and the 2,800 natural gas (or methane gas) street lights (found in Boston’s historic districts) account for 9% of total municipal GHG emissions. Street lighting used to make up a much larger share of Boston’s municipal GHG profile; however, aggressive conversions of electric street lights to LEDs dating back to 2010 have cut emissions from street lights in half. While gas lamps comprise just 4% of total street light fixtures, they produce 37% of GHG emissions from street lights.
- The electricity emissions factor decreased as described in the community inventory.
- Emissions from methane (natural gas) and fuel oil use have decreased since FY05 as the City converted some older schools from fuel oil to natural gas (or methane gas), and opened new, energy-efficient buildings that use methane for heat and hot water.
- Beginning in FY15, Boston saw a dramatic reduction in fuel oil use due to the closure of the Boston Public Health Commission’s Long Island facility, which relied primarily on fuel oil as a heating source.
- Electricity use has decreased over the long term, primarily driven by the near complete conversion of Boston’s 66,000 electric streetlights to more efficient LED fixtures. Boston has also invested in building energy efficiency measures on a project-by-project basis, and is engaging in deeper energy efficiency retrofits as part of the Renew Boston Trust.
- Steam use has decreased over the long term due to the reduction in steam use at City Hall and Copley Library and the conversion of the West End Branch library from steam to natural gas (or methane gas).
- Boston Public Schools have adopted a policy to transition the bus fleet from diesel to propane, which offers a slight carbon benefit but reduces nitrogen dioxide (NOx) emissions by up to 95% compared to diesel.
In 2015, Mayor Walsh signed on to what is now known as the Global Covenant of Mayors (GCoM), which required the City to follow the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC). ICLEI Local Governments for Sustainability, whose guidance the City already followed, was a co-developer of the GPC, so the differences were not major. The two main changes were in the categories in which the data is collated, and in two new categories of emissions collected. The GPC requires the ethanol content of gasoline to be reported as a separate biogenic source of emissions, and for an accounting of fugitive gas emissions from the natural gas (or methane gas) supply system.
Boston’s GHG inventories are reported in CO2 equivalents (or CO2e) which is a universal unit of measurement that accounts for the global warming potential (GWP) of different greenhouse gases. Boston’s GHG inventory includes carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), and uses Global Warming Potentials (GWPs) from the latest version of the International Panel on Climate Change (IPCC) Guidelines (currently 5AR). The formula used to determine the CO2e from a given energy use is Activity Data x Emissions Factor1+2+3 = GHG Emissions from the activity.
Boston currently is choosing to report at the GCP BASIC level, which covers scope 1 and scope 2 emissions from stationary and transportation sources, as well as scope 1 and scope 3 emissions from waste.
- Scope 1: GHG emissions from sources located within the City boundary.
- Scope 2: GHG emissions occurring as a consequence of the use of grid-supplied electricity, heat, steam, and cooling within the City boundary.
- Scope 3: All other emissions that occur outside the City boundary as a result of activities taking place within the city boundary.
Our full methodology may be found in “Boston Greenhouse Gas Inventory Methodology,” most recently updated for the 2016 inventory year.
2019 data revisions
- The City received updated methane consumption data for 2017 and 2018, in addition to 2019.
The Local Government Operations inventory methodology for calculating GHG emissions is based on the ICLEI greenhouse gas reporting protocol for local government operations, developed by ICLEI and the National Association of Clean Air Agencies. The protocol categorizes emissions as direct (Scope 1) or indirect (Scope 2). Direct emissions come from the burning of natural gas (or methane gas), fuel oil, gasoline, diesel fuel, and other fuels in the City’s facilities, vehicles, and other equipment. Indirect emissions come from the burning of fuels in facilities owned and operated by others to produce electricity, and steam that the City uses. Emissions that are not under the operational control of the City government, or involve leased properties, are excluded. Emissions from the Boston Housing Authority, the Massachusetts Water Resources Authority (MWRA), and the Boston Planning and Development Agency (BPDA) are not included in the inventory. Those from the Boston Public Health Commission (BPHC), and the Boston Water and Sewer Commission (BWSC) are.
In 2013, the City invested in an Enterprise Energy Management System (EEMS) and an Energy Manager to track and report local government energy consumption, cost, and GHG emissions. Prior years’ reporting relied on annual data collection from numerous stakeholders in the auditing, budget, and purchasing offices. This manual process sometimes led to inconsistent data collection from year to year. Now the process is almost entirely automated, and with complete invoice data for over seven calendar years entered, the City can track progress towards energy and GHG reduction goals on a monthly basis. By tracking this data more closely, the City is able to identify which departments, buildings or assets are contributing most to our overall portfolio, and in the process, has identified errors in utility bills worth over $1.2 million in credits back to the City.