Does Peatland Degradation Contribute to Global Climate Change?
Introduction
Global warming due to the release of greenhouse gases (GHG) from the combustion of fossil fuels and the resultant climate change is arguably the most well-known anthropogenic driving factor in this process (Cook et al., 2013). Whilst there are multiple GHG emissions of concern, carbon dioxide (CO2) is the primary emission driving anthropogenic climate change with substantial contributions from methane (CH4; Hook and Tang, 2013). However, whilst the majority of CO2 linked to climate change is indeed released from fossil fuel combustion this does not mean that this is the sole source of CO2 that result in climatic forcing (Mortoja and Yigitcanlar, 2020). There are multiple additional sources of CO2 and CH4, that are less frequently considered within the context of anthropogenic climate change. Some examples of these additional sources include: CH4 from cattle, CO2 releases from melting ice caps and glaciers and CO2 and CH4 releases from organic matter degradation under aerobic or anaerobic conditions respectively (Gao et al., 2012; Wallace et al., 2015; Hossain et al., 2017).
The reason why these additional sources may get slightly overlooked is due to the perceived magnitude of the climatic forcing resulting from these releases in comparison to those attributed to the emissions from fossil fuel combustion (Bauska et al., 2015). It is suggested that this may be an oversight that could have extensive implications for future climate change if strategies are not developed to control additional GHG emissions from sources other than fossil fuels (Sitch et al., 2015). In the following essay a potentially substantial source of CO2 and CH4 emissions, that of global peatlands, is considered in terms of the both the current magnitude of emissions and the likely magnitudes of future emissions. This will include a discussion of whether there is sufficient attention given to the GHG emissions from this source and what strategies should be considered within future management prospects to limit peatland GHG releases.
Peatlands within the global carbon cycle
Peatlands are important to the global carbon cycle due to the extensive carbon store that they represent (Qiu et al., 2020). The storage of carbon in peatlands is in the form of organic matter than has been deposited and only undergone a small degree of decomposition (Qiu et al., 2020). The reduced rate of organic matter decomposition in peatlands is due to the environmental parameters, the high-water content reduces the oxygen availability and thereby inhibits the occurrence of aerobic decomposition (Corbett et al., 2015). Aerobic composition is a more rapid and complete process than that of anaerobic decomposition (which occurs when there is little to no oxygen present in an environment; Corbett et al., 2015). Thus, in peatlands, instead of the organic matter being broken down and released as CO2 emissions to the atmosphere, this carbon-based matter is stored within the peatland soil horizons (Alexandrov et al., 2020). As the rate of vegetation production on the surface exceeds the rate of organic matter decomposition accumulation occurs (Turetsky et al., 2015). There will be some breakdown of the organic matter due to anaerobic decomposition and this process produces CH4 emissions although these emissions are several orders of magnitude lower than the CO2 emissions that would be expected under aerobic conditions.
Peatlands occur across the globe in various climatic conditions ranging from the arctic to the tropics totalling approximately 3% of the global land area (Yu et al., 2011). It is estimated that the global peatlands store approximately 600 gigatons of carbon (Yu et al., 2011). This represents roughly 25% of the carbon that is stored in soils globally (Turetsky et al., 2015). Therefore, it can be observed that whilst peatlands are only a small fraction of the global soils, they are highly important due to their function as a significant carbon sink and storage pool.
Peatland contributions to Climate Change
In a natural state peatland accumulate carbon from plant biomass that is subsequently stored and thereby not emitted to the atmosphere. However, the disturbance of a peatland changes the environmental conditions and can result in the stored carbon being released to the atmosphere via aerobic decomposition processes (Aslan-Sungur et al., 2016; Valdes-Barrera et al., 2019). Whilst this can occur through natural process, the predominant mechanism is due to anthropogenic disturbance of peatland ecosystems. In particular, the draining of peatlands for use in agriculture has been noted as a significant factor in the destruction of peatlands. A study published by Frolking et al., (2011) suggests that approximately 10 to 20% of global peatlands have been disturbed for the purpose of either agriculture or forestry, resulting in substantial carbon fluxes to the atmosphere.
At the present time peatlands are still classified as an overall carbon sink, thereby being considered a positive asset in managing atmospheric carbon with regards to global climate change (Loisel et al., 2021). However, recent studies, such as that published by Loisel et al., (2021) suggest that in the coming decades peatlands will cease to be a carbon sink and will instead become a net carbon source. This means that peatlands are likely to become a contributor to climatic forcing due to the emissions of carbon exceeding the sequestering of carbon within these biomes. This predicted change to a carbon source rather than sink is suggested in part due to the conversion of peatlands to other land use purposes as described in the previous paragraph and in part due to the changing environmental conditions occurring attributable to the impacts of climate change (Loisel et al., 2021).
The changing environmental conditions stemming from climate change include alterations to precipitation patterns increasing the likelihood of prolong periods of extreme droughts in many locations (Mukherjee et al., 2018). Several published studies have noted that increased drought frequency has a detrimental impact on peatland carbon storage. Kang et al., (2018) noted that extreme drought reduced vegetation productivity and thereby decrease organic matter inputs into the peatland for an overall 11.3% decrease in the carbon storage potential of peatlands located in the Zoige plateau of Tibet. The reduction of organic matter inputs in combination with increases in atmospheric carbon fluxes from peatlands under future climate change has significant implications for atmospheric CO2 concentrations (Ribeiro et al., 2021).
Are peatlands appropriately considered within the sphere of management strategies?
The high potential for substantial carbon releases and reduction in carbon storage of the global peatlands under future climate change scenarios suggests that these ecosystems are highly important and should be appropriately managed to reduce climate change contributions. However, there have been several recently published studies that indicate that peatlands are not effectively incorporated into climate change prediction models (Ribeiro et al., 2021; Loisel et al., 2021). Page ad Baird (2016) suggest that there is an urgent need for more robust incorporation of peatlands into climate models to accurately account for the impact that these ecosystems may have on further climate change. Warren et al., (2017) highlight that there are still multiple uncertainties regarding peatland functioning under future climate change that need to be addressed through further research to aid in accurately accounting for the potential impact of peatlands in the future. Whilst Harenda et al., (2018) and Leifeld and Menichetti (2018) suggest that the potential role of peatland restoration in climate change mitigation strategies is underexploited. The general consensus in the published literature appears to be one suggesting that the role of peatlands in future climate change is not sufficiently understood and thereby inhibits the development of appropriate management strategies that could result in a positive impact of peatlands on climate change rather than a role as a contributory factor.
Conclusion
Peatlands are important global ecosystems that play a significant role in the sequestering of carbon. Current studies indicate that there is a high likelihood that future climate change will negatively impact the functioning of many areas of global peatlands resulting in a reduction in carbon sequestration and the release of previously stored carbon. It has been suggested that in the coming decades many peatland areas will be impacted by changing environmental conditions and thereby present a net flux of carbon to the atmosphere subsequently contributing to climatic forcing and global climate change. Therefore, whilst there is limited evidence to suggest that currently peatlands present a significant contribution to global climate change, it is highly likely that this will change in the future and that peatland will be a substantial contributor to climate change occurrence. It is evident the further research is required to adequately understand the role that peatlands are playing and will play in global climate change to enable both accurate modelled predictions and the development of effective management strategies to preserve these carbon stores.
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