Peat (turf) is an accumulation of partially decayed vegetation. One of the most common components is Sphagnum moss, although many other plants can contribute. Soils that contain mostly peat are known as a histosol. Peat forms in wetland conditions, where flooding obstructs flows of oxygen from the atmosphere, reducing rates of decomposition.
Bogs are the most important source of peat, but other less common wetland types also deposit peat, including fens, pocosins, and peat swamp forests. There are many other good words for lands dominated by peat including moors, muskeg, or mires. Landscapes covered in peat also have specific kinds of plants, particularly Sphagnum moss, Ericaceous shrubs, and sedges (see bog for more information on this aspect of peat). Since organic matter accumulates over thousands of years, peat deposits also provide records of past vegetation and climates stored in plant remains, particularly pollen. Hence they allow humans to reconstruct past environments and changes in human land use.
Peat is harvested as an important source of fuel in certain parts of the world. By volume, there are about 4 trillion m³ of peat in the world covering a total of around 2% of global land area (about 3 million km²), containing about 8 billion terajoules of energy.
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 1mm per year, and as it is also reported that peat regrowth takes place only in 30-40% of peatlands. It is for these reasons that the UN do not classify peat as 'renewable' but as a fossil fuel. Similarly the IPCC do not classify peat amongst renewable biomass or biofuels, due to the length of time for peat to re-accumulate after harvesting, but as a fossil fuel.
Peat fires have been responsible for some large public health disasters, including the 1997 Southeast Asian haze.