Mires, particularly bogs, are the most important source of peat, but other less common wetland types also deposit peat, including fens, pocosins, and peat swamp forests. Other words for lands dominated by peat include moors, or muskegs. Landscapes covered in peat also have specific kinds of plants, particularly Sphagnum moss, Ericaceous shrubs, and sedges. 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. 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 1mm 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 "slow-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).
Peat fires have been responsible for some large public health disasters, including the 1997 Southeast Asian haze.