What default carbon dioxide figure does the Intergovernmental Panel on Climate Change give per tonne of aluminium for anode use, and when should I replace it?
The Intergovernmental Panel on Climate Change (IPCC) 2006 Tier 1 default is 1.6 tonnes of carbon dioxide (CO2) per tonne of aluminium for prebake cells and 1.7 for Søderberg, each with 10% uncertainty. A better figure uses net anode use: carbon per tonne of aluminium times 44/12, less sulphur and ash.
Where the carbon goes
In the cell, carbon from the anode reacts with alumina: 2Al2O3 + 3C gives 4Al + 3CO2. The guide calls the consumption of prebaked anodes and Søderberg paste the principal source of process CO2. Other process sources linked to baking prebake anodes are under 10 percent of the total non-energy CO2.
Fuel burnt to bake anodes, to mine and refine bauxite, and the fossil electricity used are covered under Energy in Volume 2. The guide warns against counting CO2 twice between the two chapters.
The Tier 1 defaults
- Prebake: 1.6 tonnes of CO2 per tonne of aluminium, uncertainty 10%.
- Søderberg: 1.7 tonnes, uncertainty 10%.
- Both come from International Aluminium Institute data. The prebake figure includes CO2 from burning pitch volatiles and packing coke in the anode baking furnace.
- You only need to split production between prebake and Søderberg, not by finer cell type.
Replace the default with your anode record
For prebake cells, Tier 2 and 3 use Equation 4.21: CO2 = net anode consumption x metal produced x (100 minus sulphur % minus ash %) / 100 x 44/12. Net anode use per tonne of aluminium and metal production are the two inputs that matter; the guide's uncertainty for them is 5% and 2%.
For the small terms, Tier 2 uses industry typical values of 2% sulphur and 0.4% ash in baked anodes. Tier 3 uses your own anode analysis. The guide expects Tier 3 to improve accuracy by no more than about 5 percent.
For Søderberg cells the guide uses Equation 4.24 instead, and the key inputs are paste consumption per tonne of aluminium and the binder content of the paste.
What is not in these numbers
Perfluorocarbons from anode effects are a separate calculation, covered on the aluminium PFC page. A 2004 industry survey cited by the guide found no evidence of sulphur hexafluoride emitted from smelting by the Hall-Heroult process.
A prebake smelter making 100,000 tonnes a year (example)
- Tier 1: 100,000 x 1.6 = 160,000 tonnes of CO2
- Own record: net anode use 0.42 tonnes of carbon per tonne of aluminium, sulphur 2%, ash 0.4%
- 0.42 x 100,000 x (100 minus 2 minus 0.4) / 100 x 44 / 12 = about 150,300 tonnes
- The default is about 9,700 tonnes higher for this smelter
Output and anode use are example numbers. Pitch volatiles and packing coke add small separate terms for baking furnaces.
What Senseible does here
Senseible reads fuel invoices and electricity bills into monthly records, so the fuel and power around the cells are on file for each month. Anode weights come from your own plant records.
- Free calculators
- Aluminium perfluorocarbon defaults by cell
- Captive coal power and aluminium CBAM
- Jharsuguda smelter anode CO2 per tonne
Last reviewed 2026-11-04. Defaults are from the 2006 IPCC Guidelines, which cite 2000 and 2005 industry data. Prefer your own anode records where a buyer or verifier will accept them.