How to Allocate GHG Emissions Reductions Among Mitigation Measures

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Climate planning is a relatively new science.  And like all sciences still in their infancy, numerous methodologies exist for accomplishing essentially the same task.

There are many aspects to developing a climate plan, however aspects fundamental to all climate plans include:

  1. developing an inventory of greenhouse gas emissions for a given jurisdiction,
  2. identifying which federal, state, and local greenhouse gas mitigation measures to include in the climate plan,
  3. setting realistically achievable greenhouse emissions reductions targets,
  4. determining how much each mitigation measure contributes to reaching the targets,
  5. and finally developing an implementation and monitoring strategy.

EPIC has just released a paper focusing on the fourth step.  Properly determining how much each mitigation measure contributes to reaching the greenhouse gas reduction targets is a very important step, and prone to modeling mistakes.

Climate planning documents regularly feature forecast greenhouse gas emissions curves that just barely hit a desired future emissions target. Further, interested parties frequently and contentiously debate the underlying assumptions that comprise individual mitigation measures out to the very last decimal. For these reasons, insuring that the affects of each greenhouse mitigation measure are properly accounted for is crucial.

A commonly used method for measuring greenhouse gas emissions is to multiply the total level of a particular activity (e.g., electricity consumption) by an emissions factor associated with the same activity (e.g. lbs CO2e/MWh). While this relation is efficient at measuring total GHG emissions, it has limitations when used to determine emissions reductions.

Here’s the question:

How should emissions reductions be allocated between two or more mitigation measures that simultaneously reduce overall greenhouse gas emissions, where some measures affect the total level of a particular activity (e.g., electricity consumption), and other measures affect the emissions factor (e.g. lbs CO2e/MWh)?

Addressing this problem is the subject of EPIC’s most recent technical working paper.

A seemingly natural solution to this problem is to calculate the effects of all the various mitigation measures sequentially. This method leads to the correct answer for total greenhouse gas emissions reductions, but will lead to incorrect results for the emissions reductions attributable to each individual mitigation measure. Indeed, this method will yield emissions reductions allocations that are wrong by ±10-15% for certain mitigation measures.

EPIC’s latest paper provides a solution to this problem within the electricity sector. In the paper we derive a refined methodology that minimizes methodological errors in allocating greenhouse gas emissions reductions, without overly complicating the calculation procedure.

Be on the lookout for a complimentary paper focusing on the transportation sector to be released soon.

Please feel free to contact EPIC with any questions or comments.

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About Clark Gordon

Mr. Gordon is an Energy Policy Analyst at EPIC. His contributions to EPIC focus largely on energy and greenhouse gas emissions modeling. Recent work includes aiding in the design and development of a community-scale greenhouse gas emissions model, capable of forecasting both business-as-usual emissions levels and dynamic mitigated emissions levels for each city within the San Diego region.
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