Burning peat releases about 106 kg of carbon dioxide per gigajoule of fuel heat, more than bituminous coal at 94.6 and lignite at 101, and wood at 112 only balances out if the trees regrow at the rate they are cut. Peat cannot be balanced this way, because the carbon in a bog took thousands of years to store and a cut-over bog keeps releasing it as it dries.
Part of Peat Harvesting
The carbon cost of burning peat compared with coal and coppice wood, using standard emission factors, and why renewability changes the sum.
Source And Basis
The emission factors below are the IPCC 2006 Guidelines default values for stationary combustion, in kg of CO₂ per terajoule of fuel on a net calorific basis (1 TJ = 1,000 GJ): other bituminous coal 94,600; sub-bituminous 96,100; anthracite 98,300; lignite 101,000; peat 106,000; wood and wood waste 112,000. They are recalled from the published tables and should be checked against the source if you can. They cover burning only: not mining, drying, haulage, or the emissions from a drained bog.
Worked Example: Per Gigajoule And Per Tonne
Inputs: the factors above; net heat values from BTU Content Compared to Wood (peat at 30% moisture 12.9 GJ/t, air-dried wood at 20% 14.3 GJ/t) and bituminous 27 GJ/t and lignite 12.5 GJ/t (midpoints of the coal parent’s ranges).
| Fuel | kg CO₂ per GJ | GJ per tonne | kg CO₂ per tonne |
|---|---|---|---|
| Peat, 30% moisture | 106 | 12.9 | 106 × 12.9 = 1,367 |
| Lignite | 101 | 12.5 | 101 × 12.5 = 1,263 |
| Bituminous coal | 94.6 | 27 | 94.6 × 27 = 2,554 |
| Wood, 20% moisture | 112 | 14.3 | 112 × 14.3 = 1,602 |
For 50 GJ of fuel heat in a year (an assumed round number for comparison): peat 50 × 106 = 5,300 kg; bituminous 50 × 94.6 = 4,730 kg; wood 50 × 112 = 5,600 kg. Per unit of heat peat releases about 12% more than bituminous coal (106 ÷ 94.6 = 1.12).
Why Wood And Peat Differ In Kind
Wood’s higher factor is not the full story. Carbon from a tree that regrows is taken back up, so coppice wood used at a steady cut rate roughly nets to zero over the rotation: the carbon released in one year is recaptured by the shoots growing back (Coppicing & Fuel Management). That assumes the cut and the regrowth are matched, and it counts nothing for the work of cutting and carrying.
Peat has no such offset. A bog adds depth at 0.5-1 mm a year (parent), so the carbon returned to the air by burning would take thousands of years to recapture. In addition, a cut-over or drained bog is exposed to air, and its remaining peat then oxidises and releases more carbon. The size of that release is not stated in the parent article and is not given here, but its direction is certain: a bog drained for fuel loses carbon beyond what the fire releases.
Common Mistakes
- Treating peat like wood. Wood may be balanced by regrowth; peat is a store that is spent.
- Quoting emission factors without a basis. These are per unit of net heat, not per tonne.
- Leaving out the drained bog. The factors cover only the burning.
Safety
A drying bog is also a fire risk
The same drying that releases carbon makes peat flammable, and a peat fire releases it fast and burns underground for months. Keep ignition sources off cut-over bogs (Environmental Considerations).
What’s Next
- Learn next: Sustainable Harvesting Limits — how much to cut at all
- Combine with: Coal Surface Mining — the other fossil fuel