One-page EEIO intro with overview diagram

figures/figures.csv

@@ -5,3 +5,4 @@ io-tables-to-a,io/index.md,diagram (SVG),hand-made,,,draft
 io-mrio-blocks,io/index.md,diagram (SVG),hand-made (after CEDA team slide 19),,,draft
 country-tiers-map,io/country-tiers.md,map (SVG),data/country_tiers.csv + Natural Earth 1:50m admin-0,figures/scripts/tier_map.py,,draft
 ghg-pipeline,ee/index.md,diagram (SVG),hand-made,,,draft
+eeio-overview,intro/what-is-eeio.md,diagram (SVG),hand-made,,,draft

intro/what-is-eeio.md

@@ -3,32 +3,39 @@ title: "What is an EEIO model?"
 ---
 
 :::{tip} Summary
-*To be written.*
+An environmentally-extended input-output ({term}EEIO) model combines data of how outputs produced by sectors in an economy serve as inputs for other sectors along with environmental attributes of each sector. When the economic data is extended with environmental data this way, such as with GHG emissions, the resulting model can produce emission factors that represent the GHG emissions across a whole supply chain per dollar spent on a sector's products.
 :::
 
-:::{note} Draft placeholder
-:class: dropdown
-Plan §3.1.1 · target: **RC (Oct 27)**
+:::{figure} ../figures/diagrams/eeio-overview.svg
+:label: fig-eeio-overview
+:alt: Two grey boxes on the left feed arrows into a central box labeled EEIO model. The upper box, input-output tables, shows a small grid of cells and is described as dollars flowing between sectors and to final users, with the letters V, U, A, and L. The lower box, environmental extension, shows a row of shaded cells labeled CO₂, CH₄, and so on, and is described as greenhouse gases emitted by each sector, with the letters E, B, and C. The EEIO model traces emissions through every round of suppliers. An arrow from it leads to a highlighted box, emission factors D and N, in kilograms of CO₂e per dollar of purchases, by sector and country.
+An EEIO model combines input-output tables with an environmental extension to produce emission factors.
+:::
 
+## Where EEIO comes from
 
-**Planned content**
+EEIO grew out of economic input-output analysis when economist Wassily Leontief added the pollution generated by each sector to his model of the economy [@leontiefEnvironmentalRepercussionsEconomic1970], and it has been a basis for carbon footprinting of nations, organizations, and products over the last few decades [@minxInputOutputAnalysisCarbon2009].
 
-- Why spend-based supply chain emission factors exist and what they answer: the cradle-to-gate emissions per dollar of purchases from sector X in country Y
+## The parts of the model
 
-**Key visuals**
+Each data component is put into a matrix, named by a letter that is common in input-output analysis and used throughout these docs (see [](../reference/notation.md)). Input-output analysis then combines the matrices with matrix algebra.
 
-- 🖼 Story graphic: a $1 furniture purchase → the furniture maker buys wood, metal, electricity, transport → each of those buys from others, some abroad
-:::
+- **Input-output tables.** The supply (`V`) and use (`U`) tables record which sectors produce which products, and which products each sector and final user buys. From them come the direct requirements (`A`), the inputs a sector buys per dollar of its output, and the total requirements (`L`, the Leontief inverse), which add up the purchases through every round of suppliers. See [](../io/index.md).
+- **Environmental extension.** Emissions of each gas by each sector (`E`), divided by the sector's output, give the direct emission intensities (`B`). Characterization factors (`C`) convert each gas to CO₂-equivalent. See [](../ee/index.md).
+- **Emission factors.** Combining the two gives the direct emission factors, `D = C × B`, for what a sector emits itself, and the total emission factors, `N = C × B × L`, for what is emitted across its whole supply chain.
+
+## EEIO and life cycle assessment
+
+An EEIO model has the same matrix structure as the models used for life cycle assessment (LCA) [@suhDevelopingSectoralEnvironmental2005]. In both, a matrix of the inputs each activity needs is inverted to trace every upstream supplier, and a matrix of emissions per unit of each activity is multiplied through it. The difference is that EEIO describes sectors in dollars, where LCA usually describes individual processes in physical units. Because of this shared structure, EEIO data can serve as background data in LCA, as discussed in {cite:t}`ingwersenConsideringInputoutputDerived2026`.
 
-## Learn more
+## Multi-regional models
 
-- **From the field:** USEEIO supply chain factors [@ingwersen_supply_2022]
-- **Cornerstone papers:** *to be added*
-- **Code:** *to be added*
+A single-country model assumes imported products are made the same way, and with the same emissions, as products made at home. A multi-regional input-output ({term}`MRIO`) model instead links countries' input-output tables through international trade, so each import carries the supply chain and emissions as it was produced in the origin country. For the companies reporting to the Carbon Disclosure Project (CDP), in one study using an MRIO model instead of a U.S. single-region model raised their estimated upstream emissions by about 10% [@davisImportanceMultiregionalAccounting2025]. The Cornerstone model is an MRIO model; see [](../io/index.md#from-single-country-tables-to-the-multi-region-model).
+
+
+## Further reading
+
+For a book-length introduction to EEIO and its use in LCA, see {cite:t}`hendricksonEnvironmentalLifeCycle2006a`.
 
 +++
 
-:::{div}
-:class: page-status
-Applies to: RC · Last reviewed: RC
-:::

myst.yml

@@ -20,14 +20,7 @@ project:
       output: exports/cornerstone-eeio-guide.pdf
   toc:
     - file: index.md
-    - title: Introduction to EEIO models
-      children:
-        - file: intro/what-is-eeio.md
-        - file: intro/io-part.md
-        - file: intro/multi-regional.md
-        - file: intro/ee-part.md
-        - file: intro/emission-factors.md
-        - file: intro/uses-and-limits.md
+    - file: intro/what-is-eeio.md
     - title: The IO model
       children:
         - file: io/index.md