Australian Grid Reality Index

Methodology

How the index works

Australian businesses report location-based Scope 2 emissions by multiplying their electricity use by one NGA factor per state, fixed for the whole reporting year. The grid behind that factor changes every five minutes. The index shows, each month, how far the real grid sat from the factor. The NGA factor remains the correct number for compliance under NGER and ASRS; the index shows what a single annual average hides.

State index. For each NEM region and month we divide AEMO's total daily emissions by total daily sent-out energy, then divide by that state's NGA factor for the financial year the month falls in.

GRI(r,t) = 100 × ( Σ CDE(r,d) ÷ Σ E(r,d) ) ÷ NGA(r, FY of t)

Monthly values are energy-weighted (total emissions over total energy), never an average of daily values, so a low-demand Sunday counts for less than a heatwave Tuesday.

NEM index. AEMO's NEM-wide intensity divided by the state NGA factors weighted by each region's sent-out energy that month. AEMO publishes no equivalent for WA or the NT, so this is a NEM index rather than a full national one.

GRI(NEM,t) = 100 × CDEII(NEM,t) ÷ ( Σr E(r,t) × NGA(r) ÷ Σr E(r,t) )

Boundary differences. AEMO built its intensity index for market settlement, not corporate reporting. It counts power where it is generated and ignores flows between states, which makes SA and TAS look far cleaner than the power their businesses use. SA and TAS are therefore published as supplementary figures until a consumption adjustment is added. AEMO's generator factors also include upstream fugitive emissions that the NGA Scope 2 factor leaves out. That biases the index towards 100, so the true gap is likely slightly larger than shown.

Provisional months. The 2026–27 NGA factors are not yet published. July to November 2026 are compared against the 2025–26 factors and will be restated once, when the new edition is released. No other revisions are made, matching AEMO's own policy.

Release. Monthly, about seven business days after month end, once AEMO has published the final billing week.

Sources and definitions

Australian Grid Reality Index. 100 × actual grid emissions intensity ÷ NGA Scope 2 factor for the same state and financial year. 88 means the grid ran 12% cleaner than the factor implies; 105 means 5% dirtier.

Grid emissions intensity. AEMO Carbon Dioxide Equivalent Intensity Index (CDEII): daily total emissions (t CO₂-e) and sent-out energy (MWh) from scheduled and market generating units, published weekly. Source: AEMO, CDEII Procedures v4.1 and CO2EII summary results.

NGA Scope 2 factor. Location-based Scope 2 factor by state, per financial year, as published by the Clean Energy Regulator. 2025–26: NSW & ACT 0.64, VIC 0.78, QLD 0.67, SA 0.22, TAS 0.20 t CO₂-e/MWh. Year-to-date NEM: actual 0.566 vs blended factor 0.639 t CO₂-e/MWh.

Roadmap

1. Consumption adjustment using interconnector flows, so SA and TAS become headline regions.
2. Five-minute intensity rebuilt from AEMO dispatch data and generator emission factors.
3. Timing gap by business type: the same kWh measured in carbon for a 9–5 office, a 24/7 cold store, a night-shift plant and an EV fleet.
4. Western Australia added from WEM public data.

Sources: AEMO, Carbon Dioxide Equivalent Intensity Index Procedures v4.1 and CO2EII summary results; Clean Energy Regulator, NGA Scope 2 factors. Calculations by NetNada Climate Lab.