GREET your vehicle?

Most people know that the carbon footprint of an electric vehicle, in use, is lower than that of an internal combustion vehicle. Except in the rare case that the electricity used by the vehicle is all generated from coal-fired stations, all of the literature confirms this. But what about the emissions impact of manufacturing an all-electric vehicle compared to an internal combustion engine? Well, that turned out to be a bit of a rabbit hole.

The first thing to know is that neither the automobile industry, nor the research models themselves, report data on emissions solely created during manufacture. Argonne Labs (part of the US Dept of Energy), has a comprehensive model called GREET (The Greenhouse gases, Regulated Emissions, and Energy use in Technologies Model) which seems to be the gold standard for all research at this point. GREET has been in development since at least 1999, and models everything to do with vehicular transport. It specifically separates the world into a fuel-cycle model, and a vehicle-cycle model, and what we’re after is the vehicle-cycle, which includes everything from raw materials sourcing, to manufacture, end-of-life, and recycling if applicable.

There are two challenges with GREET.

  1. The output is a “levelized” model. What this means is that it produces a number which is emissions generated per distance travelled. Even though the emissions we are interested in are generated during manufacture, GREET apportions them over the expected life of the vehicle. It tries to answer the macro question of vehicle emissions, rather than helping us to understand the manufacturing emissions cost.
  2. The model itself is incredibly detailed. Although it contains a (large) database of assumptions for all kinds of vehicle types, these will vary from manufacturer to manufacturer. It cannot know, for example, where one manufacturer sources electricity versus another. Only the individual corporations will know that.

GREET is a useful framework. It is being maintained actively by Argonne National Labs and was most recently updated in 2020. Researchers have published papers which claim to use the models, but also (necessarily) make gross assumptions about sources of materials and fuels. The independent research, therefore, can’t tell us much either.

Some of the manufacturers themselves do appear to use the framework. For example, if you read Ford’s 2020 CDP disclosures you will find that they reference the GREET 2019 model in their calculation of Scope 3 up-stream emissions footprint. They simply do not report the results for individual vehicles, but rather report on emissions in aggregate. However, GM and Fiat-Chrysler‘s filings show that they use completely different methodologies at this point, at least for disclosure.

For me, this is an unsatisfying answer. It does illustrate, however, the complexity of analyzing scope 3 emissions, and the challenge that lies ahead in understanding the true emissions associated with products we purchase. It also begs for a consistent methodology to be used across industries.

By Alec

Nerd, entrepreneur, adventurer, father, and enthusiastic amateur photographer, blogger, baker and cook. Aspiring yogi. Lifelong learner. Lives in the beautiful Pacific Northwest of the USA with Joanne, and the demanding feline Mr. Lucky Stripes.

Obligatory lawyer words: I'm just a climate nerd with an opinion. Although I work for Microsoft, please don't confuse my personal statements here with the company's official position.

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