The Role of Peatlands for the Climate
Peatlands are wetland ecosystems that can be found in many places all over the globe covering a total area of about 4.23 million km² or 2.84% of the Earth’s land surface . In peatlands, the production of organic material exceeds the decomposition, leading to an accumulation of peat over time . This is due to the soil in peatlands being constantly saturated with water, which excludes the oxygen needed for the decay process of organic material . At the same time the lack of oxygen in the soil creates a difficult environment for most plants to grow – only some specialised species can handle the anoxic conditions .
Over centuries, peatlands therefore have been disregarded as wastelands, before the potential of peat as energy source for house-heating and steam engines was discovered in the 19th century . In the 20th century, in addition to the need for more farmland, peat extraction and burning intensified with the rising demand for electric energy, and even nowadays, several countries run thermal power plants solely on peat, specifically Finland (producing up to 40% of its domestic electricity from peat and other fossil fuels) and Ireland [5, 6]. In many countries peat is still harvested and used as the main ingredient in potting soil.
Seeing peatlands as wastelands as opposed, for instance, to lush green tropical forests with great biodiversity, one might underestimate the important role peatlands have for the climate. It might not seem such an important place for carbon storage at first, because little carbon is stored in the peatlands’ plants themselves as opposed to the large trees and shrubs growing in a tropical rainforest. Yet, as initially mentioned, unlike the soil in many other ecosystems, peat builds up over the centuries and stores large amounts of carbon within it [2, 7]. Since it stores the carbon vertically by growing on top of the storage, which will eventually turn into lignite under pressure and geochemical effects , it is not limited to a maximum amount of carbon storage. By contrast, once forests become mature, carbon uptake decreases as the trees’ growth and the area for growing are limited and most carbon is stored in the living biomass .
A study by Qiu et al. (2021) estimated that in the time from 850 to 1850 CE the world’s peatlands were storing around 0.03 Gt of carbon per year, which has increased after 1850 due to increased atmospheric carbon dioxide levels and climate change to around 0.2 Gt of carbon per year . With elementary carbon having a mass of 12 g/mol and carbon dioxide a mass of 44 g/mol, the resulting conversion ratio from carbon to CO2 is roughly 3.67, therefore resulting in 0.11 Gt CO2 per year and 0.73 Gt CO2 per year, respectively, of carbon dioxide storage.
Once peatlands lose their water content, either by drainage or by falling dry, the decomposition process resumes, releasing the carbon in the form of methane and carbon dioxide, sometimes even dinitrogen oxide (laughing gas), back into the atmosphere . While the drained peatland areas amount to only 0.3% of the world’s land surface, with an emission of 2 Gt of carbon dioxide equivalents, they emit 5% of the world’s anthropogenic carbon dioxide . At present, an amount of 500 Gt of carbon, translating into 1835 Gt carbon dioxide, is still stored in the world’s peatlands, which is around double the amount stored in all the world’s forests [7, 10, 11]. To put that amount in perspective, with a left-over carbon budget of little more over 260 Gt as of writing this article for the 1.5 °C warming scenario, and 1000 Gt left for the 2°C scenario , it becomes clear, that we need to stop extracting peat and save the remaining peatlands from falling dry under any circumstances in order to prevent the release of large amounts of additional carbon dioxide which would make it impossible to keep climate change within relatively safe levels.
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