Sustainability in operations: the boundary is the claim
Introduit| English | Sens |
|---|---|
| carbon footprint/ˈkɑːbən ˈfʊtprɪnt/ | The total greenhouse-gas emissions, measured as carbon dioxide equivalents, caused by an activity or product. |
| system boundary/ˈsɪstəm ˈbaʊndəri/ | The chosen limit of what is counted in a life-cycle or carbon-footprint estimate. |
The sponsor wants a carbon-neutral bun
- Whether the claim survives arithmetic depends entirely on where the boundary is drawn - and unstated boundaries are how greenwash is manufactured.
- The operations answer has four parts: a number, a boundary, a date, and something a competitor can check.
Gate to gate
- The site's own week: electricity $9{,}600 \times 0.19 = 1{,}824$, gas $3{,}200 \times 0.18 = 576$, vans $420 \times 0.22 = 92$ - a carbon footprint 碳足迹 of 2,492 kg CO2e, which is $2{,}492/19{,}200 = 130$ g a bun.
- That is the gate-to-gate system boundary 系统边界: scope 1 (own fuel) and scope 2 (bought electricity) only.
Electricity 1,824 + gas 576 + vans 92 kg CO2e. The gate-to-gate week?
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1,824 + 576 + 92 = 2,492 kg.
2,492 kg over 19,200 buns, in grams a bun?
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2,492,000 / 19,200 = 129.8 g.
Match each item to its scope.
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Own fuel, bought power, everything else in the chain.
Cradle to gate - and the tariff trick
- Flour at 0.55 kg CO2e a kg, 923 kg a week: +508 kg. Cradle-to-gate is 3,000 kg - 156 g a bun - a 20% jump from one upstream input (scope 3).
- A renewable tariff at 0.06 kg/kWh cuts electricity from 1,824 to 576: the site's footprint halves (2,492 to 1,244) with no operational change. Honest only if the tariff is additional - the same fact makes the claim cheap to game.
Which scope - or no honest claim at all?
Place each emission in scope 1, 2 or 3 - or outside any claim that states a boundary.
Cradle-to-gate 3,000 kg over 19,200 buns, in grams a bun?
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3,000,000 / 19,200 = 156.25 g.
A renewable tariff at 0.06 kg/kWh does what to the footprint?
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Scope 2 moves with the tariff - 2,492 to 1,244, a 50% fall on site but only 42% cradle-to-gate; scope 3 needs the chain.
The tray that pays only if it comes back
- Cardboard: 42,000 trays a year at 0.22 = 9,240 and 4.2 t CO2e. Returnable trays at 5.50 on a two-week cycle: a pool of 1,615 (8,882).
- At 98% returns: 840 lost (4,620) + 42,000 washes (1,470) = 6,090 a year - saves 3,150, payback 2.8 years; emissions, pool amortised over five years, 2.4 t against 4.2 t - a 43% cut. At 95% returns the scheme loses 3,780 a year. Breakeven return rate: 96.6%.
Breakeven return rate for the tray scheme, in % (one decimal)?
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Losses must stay below 9,240 - 1,470 = 7,770 a year: 1 - 7,770/(808 x 52 x 5.50) = 96.6%.
At a 95% return rate the tray scheme:
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2,100 lost trays at 5.50 = 11,550, plus 1,470 of washing, against 9,240 of cardboard.
Three greenwash slips
- Comparing footprints across boundaries. 2,492 against 3,000 is the standard trick.
- Offsetting scope 2 while scope 3 dwarfs it. The chain is where the carbon is.
- Treating circularity as free. Every loop has a wash, a return leg and a loss rate - inside the boundary.
A footprint comparison is valid when both numbers use the same stated boundary.
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Same boundary, same date, same method - then the numbers can be compared.
Recap
- Gate-to-gate 2,492 kg a week = 130 g a bun; cradle-to-gate 3,000 = 156 g.
- The boundary IS the claim: state it, then measure inside it.
- Circularity pays when the loop's losses stay inside the number: breakeven 96.6% returns.