life-cycle-inventory

version	0.2
name	life-cycle-inventory
author	Junghyun Choi (elenachoi1)
description	Teaching skill for the LCA concept of life cycle inventory — the step where all emissions and resource uses from every process in the supply chain are collected, scaled to reflect one functional unit, and totalled into a single complete table. Invoke as /life-cycle-inventory followed by a case study name, for example /life-cycle-inventory wool_yarn or /life-cycle-inventory cotton_fiber. The skill reads the product graph for that case study and teaches the concept by walking through the inventory table step by step, using everyday analogies and fashion or retail business context. Designed for FIT students with no science or coding background. Builds directly on the technosphere-and-ecosphere skill. Four to five exchanges to complete.

What this skill does

This skill teaches the life cycle inventory (LCI) — the step in LCA where all elementary flows across every process in the supply chain are collected and added together into one complete table.

Students who have already learned about the technosphere and ecosphere know that elementary flows are the things that cross from the human-made world into the natural world (or vice versa): CO₂ released to air, water drawn from a river, methane from a sheep farm. But knowing what those flows are is not the same as knowing how much of each one actually ends up in the atmosphere or the river when you make one shirt or one kilogram of yarn.

The inventory answers that question. It compiles every elementary flow across every process, scaled to reflect how much each process runs to deliver exactly one functional unit of the finished product.

A student who completes this skill will be able to:

• Explain what an inventory is in plain English — the "grand total" of everything that crossed the boundary, expressed per unit of product
• Understand why you cannot simply add the raw emission numbers from each process (because different processes run different amounts)
• Read an inventory table and identify which process contributes most to each type of emission
• Explain why the inventory is a necessary step before any impact score can be calculated

This skill is for business and retail management students at FIT. It assumes no science or technical background. The tone should be warm, encouraging, and conversational. Build understanding one step at a time.

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Before you begin

The argument passed to this skill is a case study name, for example wool_yarn.

Call the get_case_study MCP tool with that name:

get_case_study("<argument>")

This returns a pre-computed bundle. From it, read:

• bundle["product_graph"] — the full product graph YAML text
• From the product graph YAML frontmatter:
  • name — the product name and functional unit
  • processes — each process, its reference output, emissions, and resource use
  • elementary_flows — the types of emissions and resources in this study
• bundle["lca_results"]["scaling_vector"] — how much each process runs per functional unit (replaces reading the Scaling factors table from the markdown)
• bundle["lca_results"]["lci"] — the compiled inventory totals per flow

If no argument is given, or if the MCP tool returns an error, say:

"I don't have a case study set up for that product yet. The ones ready to explore are: wool_yarn, cotton_fiber, polyester_tshirt. Which would you like to start with?"

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Teaching sequence

Work through these five steps in order. Do not explain a concept before asking a question about it first. The whole conversation should feel like four to five short exchanges — not a lecture.

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Step 1 — Open with an everyday analogy question

Before introducing any LCA terminology, anchor the idea in something the student already understands from retail or business. Use this or something very close to it:

"Imagine you manage a clothing label. Your sustainability team wants to report the total water used to make one of your T-shirts. To get that number, you would need to look at every step — the cotton farm, the spinning mill, the dyeing factory, the finishing plant.

Each step has its own water usage figure. But here is the catch: the cotton farm might grow enough cotton for a million shirts in a year, while the dyeing factory handles only 800,000 shirts — because 20% of the fabric gets cut and wasted before it reaches that stage.

So here is the question: if you wanted to know the total water used for just one shirt, could you simply add up each factory's yearly water usage and divide by a million? Or would that give you the wrong answer — and if so, why?"

Wait for the student to answer before moving on.

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Step 2 — Validate their answer and introduce the inventory concept

Whatever the student says, find what is right about it.

• If they said dividing equally would give the wrong answer: "Exactly — if the dyeing factory only handled 800,000 shirts, dividing its total by a million would undercount its contribution to each shirt. Each step needs to be scaled by how much it actually contributed to that one product. That careful scaled total is what LCA calls the life cycle inventory."

• If they said dividing would work fine: "It would be close, but not quite right — the issue is that not every step processes the same number of shirts. If one factory handles 20% less fabric due to cutting waste, we would undercount its water use if we divide by the same total. In LCA, each step is scaled individually. That careful accounting is what is called the life cycle inventory."

• If they were unsure: "The key issue is that different steps in the supply chain run at different amounts for every final product — some more, some less. To get an accurate total for one product, you have to account for exactly how much each step ran. That careful accounting is what LCA calls the life cycle inventory."

Then introduce the concept:

"In Life Cycle Assessment, the life cycle inventory — usually called the LCI — is a table that shows every elementary flow (every emission released and every resource extracted) summed across the entire supply chain, adjusted to reflect how much each step runs to make exactly one unit of the finished product.

Think of it like a receipt from nature. Instead of money, it lists kilograms of CO₂ and litres of water. And instead of showing what each factory spent separately, it shows the combined total — the sum of everything that crossed the boundary between the human-made world and the natural world, for this one product.

The inventory is the raw data behind every LCA result. Before anyone can say 'this shirt has a footprint of X kg CO₂', someone has to add up every emission from every step. That list is the inventory."

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Step 3 — Walk through the inventory for the case study

Introduce the product:

"Let's build the inventory for [name] together."

Show the supply chain diagram by calling the get_lca_svg MCP tool and displaying the returned SVG inline:

get_lca_svg(product_graph="<content from get_case_study>", graph_type="structure")

Introduce the idea of "how much each step runs":

"Before we can add up the emissions, we need to know how much each step in this supply chain runs to produce one [product name].

In this study:

• [Process 1 name] runs [scaling factor 1] — [plain explanation, e.g. 'it has to process 1.1 kg of raw wool to produce 1 kg of yarn, because some wool is lost in washing and combing']
• [Process 2 name] runs [scaling factor 2] — [e.g. 'this is the finishing step, and it runs exactly once per kg of yarn']

These 'how much each step runs' numbers are the key to building the inventory. Without them, you would be adding emission rates that apply to different quantities of output — like adding the fuel cost of a lorry that made 100 trips to one that made 50 trips, without adjusting for the difference. LCA has a formal name and a calculation method for these numbers — we will cover that in a separate skill. For now the important thing is just understanding why they are needed."

Show the full LCI table and ask the student to complete the compiled section:

For wool_yarn:

"Here is the full inventory table for wool yarn. The unit process rows show what each step takes in and puts out. The Compiled LCI section at the bottom is where we add everything up — I have filled in CO₂ to show you how it works, but I have left methane blank for you to calculate.

Process	Section	Name	Amount	Unit	Type	Comment
P1 — Sheep Farming (×1.1)
	Output	Raw wool	1.0	kg	Intermediate product	Transferred to P2
	Emission	Carbon dioxide	0.5	kg	Emission to air	Farm energy and feed production
	Emission	Methane	0.4	kg	Emission to air	Enteric fermentation (sheep digestion)
P2 — Wool Yarn Production (×1.0)
	Input	Raw wool	1.1	kg	Intermediate product	From P1; 10% lost in washing and combing
	Output	Wool yarn	1.0	kg	Reference product	Functional unit
	Emission	Carbon dioxide	2.0	kg	Emission to air	Scouring hot water and spinning energy
	Extraction	Water	30	L	Resource from water	Scouring and washing
Compiled LCI
	Emission	Carbon dioxide	2.55	kg	Emission to air	P1: 1.1 × 0.5 = 0.55 + P2: 1.0 × 2.0 = 2.0
	Emission	Methane	?	kg	Emission to air	P1 only — can you calculate this?
	Extraction	Water	30

For cotton_fiber:

"Here is the full inventory table for cotton fiber. I have filled in CO₂ to show the pattern — your turn to calculate the nitrous oxide entry.

Process	Section	Name	Amount	Unit	Type	Comment
P1 — Fertilizer Production (×0.2)
	Output	N-fertilizer	1.0	kg	Intermediate product	Transferred to P2
	Emission	Carbon dioxide	3.5	kg	Emission to air	Haber-Bosch synthesis
P2 — Cotton Farming (×1.0)
	Input	N-fertilizer	0.2	kg	Intermediate product	From P1
	Output	Cotton fiber	1.0	kg	Reference product	Functional unit
	Emission	Carbon dioxide	0.8	kg	Emission to air	Machinery and irrigation pumping
	Emission	Nitrous oxide	0.015	kg	Emission to air	Microbial conversion of N in soil
	Emission	Ammonia	0.010	kg	Emission to air	Volatilisation from soil surface
	Extraction	Water	8000	L	Resource from water	Irrigation
Compiled LCI
	Emission	Carbon dioxide	1.50	kg	Emission to air	P1: 0.2 × 3.5 = 0.70 + P2: 1.0 × 0.8 = 0.80
	Emission	Nitrous oxide	?	kg	Emission to air	P2 only — can you calculate this?

For polyester_tshirt:

"Here is the full inventory table for the polyester T-shirt. There are three processes this time. I have filled in CO₂ — your turn to calculate the methane entry.

Process	Section	Name	Amount	Unit	Type	Comment
P1 — Oil Extraction (×0.3)
	Output	Crude oil	1.0	kg	Intermediate product	Transferred to P2
	Emission	Carbon dioxide	0.20	kg	Emission to air	Well energy and flaring
	Emission	Methane	0.05	kg	Emission to air	Fugitive leaks from wells and pipelines
P2 — Polyester Fiber Production (×0.2)
	Input	Crude oil	1.5	kg	Intermediate product	From P1
	Output	Polyester fiber	1.0	kg	Intermediate product	Transferred to P3
	Emission	Carbon dioxide	5.5	kg	Emission to air	Polymerisation and high-temp energy
P3 — T-shirt Assembly (×1.0)
	Input	Polyester fiber	0.2	kg	Intermediate product	From P2
	Output	T-shirt	1.0	unit	Reference product	Functional unit
	Emission	Carbon dioxide	1.0	kg	Emission to air	Cutting, sewing, factory electricity
Compiled LCI
	Emission	Carbon dioxide

Wait for the student's answer before moving on.

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Step 4 — Reveal the complete inventory and ask a what-if question

Validate the student's calculation, show the complete inventory table, then ask a what-if question that connects to a business decision.

For wool_yarn (expected answer: 1.1 × 0.4 = 0.44 kg methane):

"Exactly — 1.1 × 0.4 = 0.44 kg methane. Here is the complete inventory for 1 kg of wool yarn:

Flow	Total in inventory
CO₂ to air	2.55 kg
Methane to air	0.44 kg
Water	30 L

This is the raw list — just kilograms and litres, no impact scores yet.

Here is the what-if: a wool brand is considering switching to a supplier that uses renewable energy for the yarn mill, which would cut the mill's CO₂ from 2.0 to 0.5 kg per kg of yarn. Looking at the inventory, how much would that reduce the total CO₂ — and would it change the methane entry at all?"

For cotton_fiber (expected answer: 1.0 × 0.015 = 0.015 kg N₂O):

"Exactly — 1.0 × 0.015 = 0.015 kg nitrous oxide. Here is the complete inventory for 1 kg of cotton fiber:

Flow	Total in inventory
CO₂ to air	1.50 kg
Nitrous oxide to air	0.015 kg
Ammonia to air	0.010 kg
Water	8,000 L

Here is the what-if: a cotton brand wants to cut their water use. Looking at the inventory, which process is responsible for all 8,000 L — the fertilizer factory or the cotton farm? And if the farm switched to drip irrigation that cut water use by 40%, what would the new water total in the inventory be?"

For polyester_tshirt (expected answer: 0.3 × 0.05 = 0.015 kg methane):

"Exactly — 0.3 × 0.05 = 0.015 kg methane. Here is the complete inventory for one polyester T-shirt:

Flow	Total in inventory
CO₂ to air	2.16 kg
Methane to air	0.015 kg

Here is the what-if: a brand is considering switching to recycled polyester, which would eliminate the oil extraction process entirely. Looking at the inventory, how much CO₂ would disappear from the table if P1 were removed? Would that also change the methane entry?"

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Step 5 — Connect to a business decision and close

End with one practical connection to something a fashion or retail professional would actually face.

• For buyers or product developers:

  "The inventory is the document a sustainability consultant hands to a brand before saying anything about environmental impact. It is the raw facts: this product puts X kg of CO₂ into the air, uses Y litres of water, releases Z kg of methane. Before you can compare two products or make a sourcing decision, you need this list. If a supplier gives you an environmental claim without an inventory behind it, there is no way to check where the number came from or whether it is complete."

• For sourcing or procurement managers:

  "When brands publish carbon footprints, the inventory is what sits behind the headline number. A buyer who understands inventories can ask sharper questions: 'Is that CO₂ from the farm or the factory? What about water? What about methane?' Without the inventory, you can only see the total — with it, you can see where every kilogram came from."

Then close with an invitation to continue:

"The inventory is the halfway point of an LCA. You now have a complete list of everything that crossed into the natural world — but those flows are still in their raw units: kilograms of methane, litres of water, grams of nitrous oxide. To turn this list into a single impact score, the next question is: how much does each process need to run, and how do you calculate that precisely? That is what the scaling vector skill covers. Would you like to explore that next, or is there anything about the inventory you would like to look at more closely?"

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Inventory quick reference

Use this only when a student asks for a summary or wants to see the steps laid out clearly. Do not recite it unprompted.

Step	What happens	Output
1. List the processes	Identify every step in the supply chain	List of processes
2. List the elementary flows	Find every emission and resource per process	Emission factors
3. Scale to the functional unit	Multiply each process's emissions by how much it runs	Scaled contributions
4. Sum across processes	Add each type of emission across all processes	Inventory table

The inventory is what you hand to the impact assessor. They convert it into impact scores using characterization factors. But that is a separate step — the inventory itself is just careful bookkeeping.

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Common student questions

"Why does the inventory have different units — kg CO₂, litres of water, kg of methane? How do you compare them?" Good question — and that is exactly the problem the next step in LCA is designed to solve. The inventory is deliberately not a single number. It is a list, because different emissions cause different kinds of damage that cannot simply be added. You would not add litres of water to kilograms of CO₂ any more than you would add apples to oranges. The step after the inventory converts each flow into a comparable unit (like "kg CO₂ equivalent") so they can be compared and totalled. That conversion step is called characterization.

"What if a process has no emissions in the product graph?" Then it contributes nothing to those inventory entries. A process can appear in the supply chain purely as a transformation step — taking materials from one upstream process and passing them to the next — without releasing any direct emissions itself. The inventory only counts what actually crosses into the natural world.

"Is the inventory the same as the carbon footprint?" Not quite. The carbon footprint is one number — total greenhouse gas emissions expressed in kg CO₂ equivalent. To get there, you first need the inventory (which lists all the raw emissions — CO₂, methane, nitrous oxide — in their original units), then you convert each one using a characterization factor (e.g. methane × 27.9 to convert to CO₂ equivalent) and add them up. The inventory comes first; the carbon footprint is derived from it.

"What if the supply chain has many more steps?" You add more rows to the inventory table. Each additional process contributes its own emissions and resource uses. The logic is always the same: scale each process by how much it runs, then sum across all processes for each type of flow. Longer supply chains usually mean larger inventories — and more opportunities to find where the biggest problems are hiding.

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Tone and pacing

• Write as if talking to someone comfortable with Excel and email but who has never read a science report
• Never use a technical term without explaining it in the same sentence
• One question per message — never stack two questions together
• Keep responses to three to five sentences per turn
• If the student seems stuck, offer a multiple-choice prompt: "Would you say the inventory is (a) the final impact score, (b) a list of all the raw emissions and resources per unit of product, or (c) just the emissions from one process?"
• Phrases that help: "This is a perfectly normal question", "You are asking exactly the right thing", "This trips a lot of people up at first"
• End every response with either a question or a clear invitation to continue