The form and function of peatlands and the distribution of peatland species depend strongly on the climate. Therefore climate exerts an important control on ecosystem biodiversity in peatlands.

Climate change is a normal condition for the Earth and the past record suggests continuous change rather than stability. The last 2 million years of Earth history (the Quaternary period) are characterised by a series of cold glacial events with warmer intervening interglacial periods. Peatlands expanded and contracted with changes in climate and sea-level. Many current peatlands started growth following the warming after the last glacial maximum. The initiation of new peatlands has continued throughout the postglacial period in response to changes in climate and successional change.

• Climate is the most important determinant of the distribution and character of peatlands. It determines the location and biodiversity of peatlands throughout the world.

• The Earth has experienced many climate changes in the past, and peatland distribution has varied in concert with these changes. Most peatlands began growth during the current postglacial period. Peatland extent has increased over the course of the last 15,000 years.

• In the constantly accumulating peat, peatlands preserve a unique record of their own development as well as of past changes in regional vegetation and climate.

• Records show that the vegetation, growth rate (carbon accumulation) and hydrology of peatlands were altered by past climate change. This information helps in making predictions of future impacts of climate change. 

  Temperature chenges during the last 150 years based on instrument data. (Source: Hadley Centre for Climate Change, UK Meteorological Office)
  Plant and organic materials are very well  preserved in the saturated peat	A close-up of Sphagnum cells from peat  approximately 4000 years old

• Peatlands affect climate via a series of feedback mechanisms including sequestration of carbon dioxide, emission of methane, change in albedo and alteration of the micro- and mesoclimate.

• Natural peatlands were often resilient to climate changes in the past. However, the rate and magnitude of predicted future climate changes and extreme events (drought, fires, flooding, and erosion) may push many peatlands over their threshold for adaptation.

  Peatlands have gradually expanded over the past 18,000 years. The figure shows the age of earliest peat growth in circumarctic peatlands as measured by radiocarbon dating. Line B shows the cumulative number of samples with different start dates for peat growth initiation (Source: McDonald et al. 2006)

• Some expected impacts of recent climate change are already apparent in the melting of permafrost peatlands, changing vegetation patterns in temperate peatlands, desertification of steppe peatlands, and increased susceptibility to fire of tropical peatlands.