Connemara IR – Sionnanach peat or turf
Image by Daniel Mennerich
Peat, also known as turf, is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs.
The peatland ecosystem is the most efficient carbon sink on the planet, because peatland plants capture CO2 naturally released from the peat, maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m [4.9 to 7.5 ft], which is the average depth of the boreal [northern] peatlands".
Sphagnum moss, also called peat moss, is one of the most common components in peat, although many other plants can contribute. The biological features of Sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed ‘habitat manipulation’. Soils consisting primarily of peat are known as histosols. Peat forms in wetland conditions, where flooding or stagnant water obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition.
Peatlands, particularly bogs, are the primary source of peat, although less-common wetlands including fens, pocosins, and peat swamp forests also deposit peat. Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss, ericaceous shrubs, and sedges (see bog for more information on this aspect of peat). Because organic matter accumulates over thousands of years, peat deposits provide records of past vegetation and climate by preserving plant remains, such as pollen. This allows the reconstruction of past environments and study changes in land use.
Peat is harvested as an important source of fuel in certain parts of the world. By volume, there are about 4 trillion cubic metres (5.2 trillion cubic yards) of peat in the world, covering a total of around 2% of the global land area (about 3 million square kilometres or 1.2 million square miles), containing about 8 billion terajoules of energy. Over time, the formation of peat is often the first step in the geological formation of other fossil fuels such as coal, particularly low-grade coal such as lignite.
Depending on the agency, peat is not generally regarded as a renewable source of energy, due to its extraction rate in industrialized countries far exceeding its slow regrowth rate of 1 mm per year, and as it is also reported that peat regrowth takes place only in 30-40% of peatlands. Because of this, the UNFCCC, and another organization affiliated with the United Nations classified peat as a fossil fuel.
However, the Intergovernmental Panel on Climate Change (IPCC) has begun to classify peat as a "slowly renewable" fuel. This is also the classification used by many in the peat industry. At 106 g CO2/MJ, the carbon dioxide emission intensity of peat is higher than that of coal (at 94.6 g CO2/MJ) and natural gas (at 56.1) (IPCC).