Measuring and Accounting for Greenhouse Gas Emissions

Institutional Inventory v. Individual ‘Footprint’

There are many online tools that let an individual or small group estimate their GHG ‘footprint’ by surveying their activities, lifestyle choices, housing, and so on. These can provide reasonably accurate and meaningful estimates of one’s carbon footprint, but even small errors in individual estimates can be significant if many such estimates are added together. In addition, families may not have (or may be reluctant to share) accurate information about their lifestyle, housing, food, and transportation choices.
For large groups or organizations, a more accurate result is obtained by measurement of emissions based on the total energy and resources used, called a GHG Inventory. It is important to be clear about boundaries—what period will be covered and what sources will be included or excluded. (For this project, your school & the entire school year, from July 1 through June 30.)

International organizations have created protocols to ensure that emissions are not overlooked and that the same GHG emissions are not counted by two or more entities. These protocols break down GHG sources into 3 ‘scopes’ based on where the emission is created and who controls it.

Scope 1: Direct emissions from sources owned or controlled by the reporting organization, including on-site combustion for heating and vehicles; also fertilizers and refrigerants.

Scope 2: Indirect emissions from on-site sources that are not owned or operated by the reporting organization but where significant emissions are created on behalf of the reporting organization. (For example:electricity, steam, or chilled water purchased for use on site.)

Scope 3: Indirect emissions from off-site sources that are not included in scope 2, including the supply chain of the reporting entity. This can include both upstream and downstream emissions from commuting, travel, waste disposal, and purchases.

Offsets: Activities that actually reduce GHG emissions. (For example:adding solar panels or wind turbines or managing forest land to actually reduce CO2.) Other users can purchase Renewable Energy Credits (RECs) to support these activities.

Scope 1 and 2 are generally considered the minimum for reporting, but most organizations include Scope 3 emissions that are paid for or reimbursed by the organization. (For example: travel via common carrier or charter to attend athletic events and conferences.)
In a GHG inventory, on-site generation from solar panels or wind turbines shows up as a reduction in purchased electricity. In order to obtain a reduced prices, however, many schools sell the Renewable Energy Credits (REC) to the company doing the installation. Two separate organizations cannot take credit for the same emission reduction, so the GHG Protocol requires the school to treat the power from the solar installation as if purchased from the grid.

According to internationally-accepted GHG protocols, greenhouse gas emissions are expressed in terms of metric tons of carbon dioxide equivalent (mTCO2e). For greenhouse gases other than CO2, their global warming potential is used to convert them to an equivalent amount of CO2.

Big Idea

  • Clear protocols for reporting and analysis can help ensure meaningful results.

Getting Started

Although the GHG inventory is a reasonably straightforward process, it has many interdependent elements, so it is desirable to enlist other teachers and students to help. Coordination is important, so it would be helpful to form a team to oversee the process—a team that could include faculty members who want to work on the project and certainly should include students (if you are at a middle school or high school). If possible, form the team at the very beginning of the project so it can be fully productive; for best results, we suggest the team plan to meet regularly, perhaps weekly. The keys to an effective team are a clear goal and people who want to work together as equals, sharing the responsibility, the work, and the credit.

Someone from the district administration could be a great addition, if they are committed to supporting the inquiry. (We have run across districts where administrators seemed to slow everything down, perhaps to make sure the schools wouldn’t be criticized.)

The GHG inventory is a great project that can help achieve existing curriculum goals, so it’s not so much a question of seeking approval as helping to facilitate the process of obtaining the data you need. (It’s all information that schools and districts track anyway, as noted in the instructions for the School GHG Calculator.

Emission Sources for Most Schools

The major sources of GHG emissions at a school are fuel for heating, electricity for lighting and cooling, and fuel for school-provided transportation. Fortunately, the school or district already has the needed information on these major emission sources. (The following recap follows the sequence of the Schools GHG Calculator included with this guide.)

1. On-Site Combustion [Scope 1]

Heating is usually the largest Scope 1 emission source. In most cases, the fuel is either natural gas or #2 heating oil. [Data source:Facilities, Maintenance, or Operations department.]

Vehicles owned by the school district produce GHG emissions, including this includes regular student busing and busing for athletics and field trips (as well as any other vehicles owned and operated by the district).

Note that this has to be calculated separately for each type of fuel (Diesel, gasoline, or natural gas) used in district vehicles. (Busing emissions for a single school can be estimated by comparing it to the district as a whole. Since actual emissions vary from bus to bus, this is not 100% accurate, but is a reasonable estimate.)

If the buses are owned and operated by an outside contractor, they are counted as Scope 3 emissions, but the calculation is the same for purposes of this GHG inventory.

[Data source:Transportation or Operations department.]

Other direct emissions – In most cases these are relatively small emission sources.

Coolants used in refrigerators and air conditioners – Many of them have global warming potentials (GWP) that are thousands of times worse than CO2.

Synthetic fertilizers release nitrous oxides, which are powerful GHG. At schools with large athletic fields or lawns, these fertilizers can cause significant emissions.

[Data source:Facilities, Maintenance, or Operations department.]

2. Electricity   [Scope 2]

In most schools, this consists of purchased electricity, a major emission source. Although the emissions are at the generating plant, the GHG are counted as part of the emissions for the users of that power. Electricity is billed in kilowatt hours (kWh), and there are specific conversion factors for each power region. In some cases, specific factors are available for each electric utility.

An interesting question arises when a school has solar panels installed to generate electricity on site. When installed by an outside contractor that then sells the electricity to the school to recoup the cost, that firm may retain the Renewable Energy Credits (RECs) and sell them to someone else. In such cases, GHG from the school’s electrical usage must be calculated as grid power, since the RECs were retained by the installer.

(A few schools in urban areas may be part of a ‘district energy’ setup that also supplies steam or hot water and/or chilled water; these are also scope 2 emissions.)

[Data source:Facilities, Maintenance, or Operations department.]

3. Indirect emissions (created elsewhere) by the school & its activities [Scope 3]

Heat, electricity, and busing generally account for 90% or more of all emissions controlled by the school district, but other sources are also found in some districts. (If regular busing is outsourced—operated by an independent contractor—those are considered Scope 3 emissions.)

There are several types of indirect emissions that are worth looking at:

Travel by faculty, staff, or students generates significant GHG emissions—including travel via bus or plane for conferences, athletic events, and competitions.

Commuting is a necessary part of the school’s operation, but is not directly controlled by the school or school district. These emissions can be significant, especially at larger schools, but there are tremendous variations according to how each person gets to school. How many people drive, how many miles they drive to and from school, and the type of vehicle, all matter—but any of these factors can vary from day to day and week to week. And the difference between urban, suburban, and rural schools is too great to allow use of an average.

For these reasons, the GHG calculator does not include emissions from commuting. Instead of investing a lot of time to estimate commuting, we suggest using that time to look at what can be accomplished by changing commuting habits. In the next section, we will discuss some ways to reduce commuting and estimate the effect of changes.

Food is very significant source of GHG emissions, including on-site emissions and the ‘upstream emissions’ generated by farming, transportation, processing, and preparation. It would be valuable to include these, but there is no easy way to calculate or even estimate the total, because it varies according to types of food, supplier, growing methods, distance traveled, types of processing, and how and where the food is prepared—which can be difficult to identify and can vary from day to day and week to week. It’s important to explore ways to improve food, reduce emissions, and estimate the effect of changes.

In the next section, we’ll look at how to use the inventory results.


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