Peatlands provide a record of their own development preserved in the peat itself. This means that it is possible to trace the changes in peatlands through time, in response to climate change and other influences such as succession and human activity. Peatlands are unique ecosystems because they preserve a record of their ecological and physical structure in water-saturated sediments, where decomposition rates are slower than production (Charman 2002). Peat is primarily formed from the dead remains of plants that once grew on the mire surface. However, when the layers of successive vegetation remains are laid down, they incorporate a range of other microscopic remains and geochemical signals of past environmental conditions. In fact, virtually everything living in or around a peatland has the potential to be preserved in the accumulating peat (Charman 2002), although there is a clear bias toward materials that are decay-resistant, such as structures rich in refractory compounds like lignin or chitin. The excellent preservation of materials in peat allows a variety of biological, physical, and geochemical techniques to be used to reconstruct past environmental conditions. Application of these methods provides a secure basis for understanding how peatlands have responded to past climate variability and change.

Peatlands also provide records of past changes in the wider landscape and environment such as regional vegetation change, atmospheric pollution and climate change. Some peat characteristics are representative of the local peatland environment and structure, and others are derived from adjacent uplands or the wider region. Thus, landscape and regional perspectives can be provided by peat stratigraphy, and compared to the developmental history of the peatland itself.

Evidence from peatlands can be used to reconstruct past changes in climate, contributing to the growing archive of information on past climate changes, as well as providing information on the ways in which peatland systems respond and adapt to climate changes. Some of the earliest evidence for climate changes in the ‘postglacial’ period came from peatlands in Scandinavia, where changes in the structure and botanical content of the peat were used to describe a series of main climate periods. For example, a change to less decayed peat dominated by Sphagnum mosses marked the start of the ‘Sub-Atlantic’ period following on from the earlier relatively dry ‘Sub-Boreal’. These Blytt-Sernander periods (named after the scientists who described them) are now known to over-simplify climate change over the past 12,000 years but some events are confirmed by more modern work, including the Sub-Boreal to Sub-Atlantic transition at around 2600 years ago.