Peatlands are affected by climate changes in many different ways but they also play an important role in modifying climate themselves. These effects are known as ‘feedbacks’. Several of these effects are covered in more detail elsewhere in this report so here we simply summarise some of the key points.

Peatlands play a key role in the global carbon cycle, acting both as sinks for carbon dioxide and as sources of methane. Both these processes have had a significant influence on global climate change throughout Earth history. It is evident from the preceding sections that the build up of large volumes of peat represents a vast quantity of carbon. The drawdown of carbon dioxide from the atmosphere to storage in peat has a net cooling effect on the climate. Any factors that either slow down (speed up) carbon sequestration represent a warming (cooling) effect on global climate. The carbon stored in peatlands during previous millennia is the basis of all the coal, oil and gas reserves now being exploited as energy sources. This is therefore a feedback that has operated throughout Earth history. Methane emissions from peatland are a further feedback to climate change. Warmer, wetter conditions enhance methane emissions increasing global temperatures, while cool, dry conditions suppress methane emissions and reduce global temperatures.

Greenhouse gases show variable atmospheric concentrations throughout the last 15,000 years. Peatlands contribute to these natural variations in atmospheric composition. During the current postglacial period, atmospheric concentrations of carbon dioxide and methane were not stable, even during pre-industrial times. Peatlands and other wetlands contributed to the natural variations in greenhouse gases, increasing methane concentrations during some periods and decreasing carbon dioxide concentrations at other times. Peatlands reduce atmospheric warming by reflecting more incoming solar radiation than forested dryland regions. Peatlands are generally more open landscapes than adjacent upland regions. Surface vegetation of mosses, sedges, grasses, low growing shrubs and open water has a much higher albedo (ability to reflect radiation) than closed canopy forest. Treeless peatlands in northern regions and oceanic areas therefore reflect much more incoming solar radiation than surrounding forested areas.
On forested peatlands, tree cover tends to be less dense than on mineral soils and there is a therefore a smaller but still significant difference in the albedo between peat and non-peat dominated areas in these regions. Furthermore, open ground in northern regions tends to have much higher albedo during the period of snow cover in winter, an effect particularly noticeable in late spring (Rouse 2000). Peatlands exert a strong effect on local microclimates such that the temperature regime and relative humidity are significantly different to those in surrounding dryland areas. The high moisture levels in peatlands, the mass of peat with a high thermal inertia and the particular characteristics of the vegetation cover modify local climate regimes. In particular, they produce higher air humidity and lower temperatures in summer. Wind speeds are also typically higher than in surrounding areas. This results in conditions that allow disjunct distributions of species, with some taxa occurring on peatlands far beyond their normal range for surrounding areas.