How Many Baked Potatoes Make a Microwave?

After I told my friend Tom about Food and Climate Change, he asked:

If switching to a microwave, how many single baked potatoes would he have to eat to offset the CO₂ generated by making the microwave?

"Food and Climate Change without the Hot Air" reports that:

  • Baking a single baked potato typically causes 2,140 gCO₂e emissions.
  • Microwaving a single potato typically causes 75 gCO₂e emissions.
  • So each time we microwave a potato instead of baking it, we typically save 2,065 gCO₂e emissions.

I found an academic paper, Environmental assessment of microwaves and the effect of European energy efficiency and waste management legislation (https://www.sciencedirect.com/science/article/abs/pii/S0048969717331224).

From that paper I extracted the following assumptions and findings:

  • The microwave will ... contribute around 416 kg CO₂e over its service life.
  • The use stage is the main contributor.
  • Putting a ruler up against the Fig.4 suggests that the Use fraction amounts to 279 kgCO₂e.
  • The Materials, Manufacturing, End of life and Transport add up to 137 kgCO₂e.

Section "2.2.2. Use of microwaves" reports:

  • Using the microwave would consume 538 kWh of electricity over its lifetime of eight years.
  • This excludes consumption of electricity in the standby mode.
  • For the latter ... the maximum standby power rating for microwaves ... should not exceed 0.5 W for units produced after 2013.
  • Based on this and assuming that the appliance is plugged in over the entire lifetime, the electricity consumption in the standby mode would equal 1 kWh.
  • Therefore, a conventional microwave would consume in total 573 kWh during its lifespan.

We can deduce that emissions from Use of the microwave can be split pro-rata into 262 kgCO₂e for cooking and 17 kgCO₂e for standby.

Therefore, the emissions from the full lifecycle of a microwave, excluding cooking, is 154 kgCO₂e.

Surprising answer to Tom's question:

Switching from baking to microwaving pays back the whole-of-life CO₂ emissions caused by buying and owning a new microwave after typically 75 single baked potatoes.

PR Genius or Dubious?

The press release from Manchester University to accompany the paper Microwaves could be as bad for the environment as millions of cars suggests new research (https://www.manchester.ac.uk/discover/news/microwaves-could-be-as-bad-for-the-environment-as-cars-suggests-new-research/) begins:

Microwaves usage across the EU alone emits as much carbon dioxide as nearly seven million cars according to a new study by The University of Manchester.

Nowhere was any comparison given to the climate impact of other forms of cooking. If this PR deterred anyone from using a microwave, and they switched to bake in an oven instead, it would be bad news indeed.



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