Wild Land News no 59, Winter 2003/2004

Peat & Global Warming Article

Dr. James Fenton warns against complacency when development, even in the name of renewable energy, threatens our precious peat reserves.

We are all familiar with peat - especially when a hill path deteriorates into a morass of black gunge! Peat consists of the undecomposed remains of plants, and it is often possible to see remains such as leaves and roots within the body of the peat and in some cases, of course, tree stumps. However, where there has been significant decomposition then all plant structures are lost - try the squeeze test: grab some wet peat in your hand and squeeze, and if it comes out between your fingers as a smooth paste then you are dealing with a highly humified (highly decomposed) peat.

Peat is found throughout the world, barring hot deserts, and occurs in any situation where dead plant material is produced faster than it can decompose. Generally, but not exclusively, these are situations where the soil is waterlogged, resulting in anaerobic conditions inimicable to decomposition. Peat tends to be common in cool climates and also in areas of acid soil, where again decomposition is low; for example, peat is common in the Falkland Islands where the climate is not particularly wet, but it is cool and the rocks are acidic. There is also moss peat up to three metres thick and five thousands years old further south in Antarctica, here, unusually, forming in aerobic conditions.

Cool temperate regions such as the British Isles provide ideal conditions for peat formation, and where it covers the landscape it is, unsurprisingly, called blanket peat! In fact, conditions are so good here that peat can blanket the landscape even in the relatively dry Caithness and over the Carboniferous limestone of central Ireland (although there is virtually none left there). Likewise, Flanders Moss west of Stirling is one of the few 'mosses' remaining that would once have covered much of lowland Scotland, most of which have been cut for fuel or drained for agriculture. How common peat bogs once were can be seen by the frequency that the words 'moss', 'bog', or even 'muir' still occur in place names in the lowlands.

However, the greatest extent of peatland occurs in Arctic Russia, Canada and Alaska where permafrost results in waterlogging of the ground, although the deepest peats are found in the coastal tropics adjacent to subduction zones - areas where the earth's crust is sinking down at the same rate as the peat is accumulating above. Borneo is an example, although many of the peatlands here are on fire and could remain burning for years.

Where peat becomes protected by overlying sediment, particularly in these coastal swamps, then it can be protected for millions of years, eventually metamorphosing into coal. It can be seen that both peat and coal are in effect stores of carbon - carbon taken out of the atmosphere by photosynthesis and stored in the ground as plant remains. Recent research has indicated that 90% of all carbon stored in soils and vegetation in the UK is in the form of Scottish peat; i.e. there is considerably more carbon stored in peatlands than in trees, woodland or other vegetation.

Global warming is mainly caused by the release of such stored carbon back into the atmosphere, whether from coal, oil, peat or vegetation loss. Where peat is actively accumulating (getting thicker) then it acts a as carbon sink, i.e. taking carbon out of the atmosphere; even where it is no longer actively accumulating, it still represents a significant store of carbon. However, peats, through their anaerobic nature, can also be a source of methane, itself a potent greenhouse gas; there is debate at present about whether the deeper Scottish peats are actively accumulating carbon year by year, or are now a net source of methane.

What is incontrovertible, though, is that Scottish peats are an important store of carbon and we should be making global warming worse if we caused them to erode so that all their carbon was oxidised back into the atmosphere. As a rule of thumb, Scottish peats get thicker at about one foot per thousand years, making them in effect a non-renewable resource. We should be conserving bogs and be wary even of siting renewable energy schemes on them: calculations suggest that at one proposed wind farm site there is of the order of 1.5 million tonnes of stored carbon in the peat. Bogs are very sensitive to changed hydrology, and it would be ironic if a renewable energy scheme, designed to slow down global warming, instead made it worse in the long term by being sited on a peat bog and helping to cause its long-term demise. Likewise, planting trees on peaty soils can, in the long term, cause oxidation of the peat, resulting in more carbon being released into the atmosphere than fixed by the trees.

It can be seen that peat bogs are a valuable global resource with an important role to play in carbon cycling. And I have not even talked about the nature conservation value, archaeological value, or wild land value of bogs.....

Dr James Fenton is an ecologist who started his career studying peat in Antartica. He is now the Nature Conservation Adviser in the Highlands and Islands for the National Trust for Scotland.