Sources of greenhouse gas emissions
Defining the system boundary
One of the problems facing an emissions audit is where to draw the boundary between things to audit and things to leave out. Some methodology documents recommend a three tiered approach1 1. For example, see the World Resources Institute guide to emissions auditing in offices,Working 9 to 5 on emissions, published as part of the GHG Initiative.
- Tier 1: Direct emissions from an organization, e.g. in power generating equipment it owns, fuel combustion in company vehicles.
- Tier 2: Indirect emissions from purchased utilities
- Tier 3: All other emissions
DUSP's position as part of a large campus and our utility supply from the cogeneration plant makes the conventional 3-tier approach less useful. Instead, this audit tries to limit the system boundary to DUSP's domain of action - e.g. rooms that we are "owners" of in the facilities database. This approach provides the best framework for action, since the emissions covered in this audit are those that DUSP has some direct control over. However, even with this approach, some edges are hard to define, such as catering.
Types of limitations
Each section of this audit lists limitations that have been identified. This audit has three types of limitation:
- Known underestimates/guesses: data that could be improved upon, or fuzzy upper and lower boundaries. Deliberate choices to remain less precise, where the complexity of obtaining precise data outweighs the usefulness of knowing it.
- Known omissions: data that are not included but should be, for example data on rail travel.
- Unknown omissions: sources of greenhouse gas emissions by DUSP that are unaccounted for.
Greenhouse gases, carbon dioxide and MTCDE
Anthropogenic emissions of greenhouse gases (GHG) are not limited to carbon dioxide, though this makes up the largest quantity emitted into the atmosphere by volume. Methane and CFCs are more damaging to the environment and must be included in the calculations, even though the quantities emitted are smaller. In order to use a single comparable measure for all emissions, quantities of other GHG are converted into an equivalent volume of carbon dioxide, based on their Global Warming Potential (GWP). For example, methane has a GWP of 23, meaning that a metric ton of methane has as much warming potential as 23 tons of carbon dioxide 2. 2. See Emissions of Greenhouse Gases in the United States 2005, published by the Energy Information Administration for an overview of accounting for the GWP of each GHG. The standardized measure is called Metric Tons of Carbon Dioxide Equivalent (MTCDE). It is used for all calculations in this audit. Where "greenhouse gases" and a different mass unit are used (e.g. 0.12 kg of greeenhouse gases per km travelled), this is already adjusted to represent carbon dioxide equivalence.
All units are given in SI units where possible to enable comparison with other studies and international data.
Time
Data used in this study come from various years. Student enrollment data is current, but all other figures are from 2005 or earlier. This introduces potential for further inaccuracies. More rapid reporting of Institute data would assist with audits of this type.
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