Carbon stocks: a carbon neutral future for the UK?

Ayushman – Year 12 Student

Editor’s Note: Year 12 student Ayushman has submitted this insightful essay to the Peterhouse College, Cambridge, annual Kelvin Science Prize essay competition. Ayushman uses numerical evidence to support his argument that increasing carbon stocks will still leave the UK facing an uphill battle to achieve carbon neutrality. CPD

Using numerical evidence, what carbon stocks could be enhanced to make the UK carbon neutral?

It is now widely accepted that global warming is the greatest threat in today’s world. It is not going to threaten only the environment but shall have significant impact on every aspect of our lives. Enhancing carbon stocks is an effective way to mitigate and even reverse this rise in temperature. This essay, using numerical evidence, argues that UK faces an uphill battle to achieve carbon neutrality just by increasing its carbon stocks.

Carbon stocks in the United Kingdom

Figure 1: Office of National Statistics (ONS) data dividing total UK biocarbon stock into sectors (8)

Carbon stocks are long term stores of carbon sequestered from the atmosphere – essentially carbon pools. The UK has both geocarbon stocks (carbon stocks in fossil fuels) and biocarbon stocks (stocks in ecosystems). For this environment-based report, we’ll focus on enhancing biocarbon stocks as they maximise environmental benefit. Figure 1 highlights the proportions of biocarbon stock within each sector. The UK’s carbon stocks contain over 4200 million tonnes of carbon. There are 5 different subtypes of biocarbon stock within the forest cover sector:

  1. Aboveground biomass (such as branches, bark and foliage)
  2. Belowground biomass (roots)
  3. Litter (non-living biomass)
  4. Wooden debris (detritus)
  5. Soil

In the United Kingdom, the majority (72%) of forest carbon is stored in the soil.

Furthermore, one can delve into which areas of the UK have the greatest carbon stock.

To summarise: wetlands and peatlands contain the most carbon by land type; carbon is mainly concentrated in the soils rather than in biomass; and Scottish peats contain more carbon than anywhere else in the UK – making their preservation paramount.

How are carbon stocks environmentally beneficial?

Carbon stocks aren’t particularly useful when sedentary – rather it is the increase in locked carbon and the subsequent [net] reduction in the release of carbon dioxide that is beneficial: by helping to mitigate the amount of [outgoing] radiation absorbed [by greenhouse gases], lessening the effects of global warming. Carbon stocks are thus a handy alternative to [attempts at de]creasing carbon dioxide emissions – hence are beneficial for the environment.

An appraisal of the UK’s environmental situation

Government statistics state that the UK’s carbon footprint in 2016 was 213.82 megatonnes of carbon (MtC), which is a 21% reduction from a decade earlier. However, this means that the UK’s annual carbon footprint is around 5% of its total carbon stock, which highlights the severity of our environmental situation.

Which carbon stocks can be enhanced and how?

This section deals with seven methods of carbon stock enhancement.

  • Afforestation – afforestation accumulates carbon stock in biomass by increasing carbon dioxide sequestration, as more trees take in more carbon dioxide for photosynthesis. Afforestation accumulates carbon mainly in the above-ground and below-ground biomass stocks.
  • Preservation of existing forests – preserving existing forests entails:
    • Preventing forests being converted to other land types (e.g. – preventing conversion of grassland to arable land);
    • Preventing detrimental agricultural practices, like tilling, from taking place on the forest lands.
    • Preservation of existing forests is particularly important in places with poor soil quality and low growth rate, as otherwise regeneration of the carbon pool would take a long time.
  • Rehabilitating existing forests – this can mean either improving damaged areas, such as by blocking peat drains to raise the water table, or it can mean conversion of existing land, from arable land to peatlands to kick-start or restart carbon sequestration. Restoration of unimproved grassland adds 1.9 tonnes of carbon per hectare to the area stock in the first year of restoration and a further 1.1 tonnes per hectare each year after that (Warner, 2008). Preservation and rehabilitation accumulates carbon in all five carbon stocks – as it prevents soil erosion through the roots holding onto soil, it increases leaf litter and wooden detritus and spurs the accumulation of both above-ground and below-ground biomass. Thus, preservation and rehabilitation of existing forests is an excellent method of accumulating carbon.
  • Organic amendments – organic matter supplementation is particularly effective in enhancing the carbon stock in soil – animal manure can be used as fertiliser to increase plant growth and accumulate carbon stock through biomass – thereby organic amendments are a simple and convenient way to increase carbon stock.
  • Conservation tillage – tillage of land is where land is prepared for cultivation by mechanically agitating it (digging, stirring, overturning) but this leaves land prone to soil erosion. Thus, conservation tillage of arable land minimises the amount of tilling one does – ideally with no tillage at all as this minimises soil erosion. The reduction of soil erosion also reduces river pollution. Conservation tillage is especially beneficial in enhancing carbon in the soil – the soil having the greatest carbon content of all the five stock types.
  • Agroforestry – agroforestry entails trees being combined with livestock and crops on the same area of land, especially useful in [Low Income Countries] LICs where good quality land is at a premium. Researchers at Penn State University (De Stefano et al., 2018) have found that agroforestry increases carbon sequestration by 34% relative to conventional farming methods – yielding a healthy increase in carbon stock. Agroforestry sees an accumulation of carbon in all five stocks.
  • Community Forestry – the local community increases their participation in local forest management by maintaining forests themselves, actively afforesting and converting derelict land into woodland – thereby accumulating carbon stock in biomass. “England’s Community Forests” is an existing initiative that supports the regeneration of forests in England, having already reclaimed 700 hectares of derelict land and converted it to woodlands in Merseyside. We can estimate the carbon stock increase of this reclamation using aforementioned data (Warner, 2008) and say that this Merseyside initiative will add over a kilotonne of carbon to existing carbon stock every single year. Community forestry helps almost to regenerate an ecosystem – which spurs the accumulation of carbon in all five stocks, like agroforestry, as well as creating good environmental care practices for the future, thus is highly recommendable.

What are the limitations of enhancing carbon stock?

However, it must be noted that the enhancement of carbon stock does vary on a number of factors, including climate (temperature and precipitation) – which can constrain organism growth and thereby the accumulation of carbon stock through biomass. The effect of climate change on UK wetlands is currently unknown, but warmer climates usually see carbon stored in wetlands to be released into the atmosphere (and oxidised in the form of carbon dioxide). The topography of the landscape also affects carbon stock, as steep valleys are prone to soil erosion and have low infiltration (where water enters the soil) as the water does not have enough time to infiltrate due to the nature of the relief in that area. This can affect plant growth – steep valleys may not have as much carbon stock in their soils as flatter areas. Furthermore, organisms themselves control the enhancement of carbon stock as it is vegetation that controls the nature of carbon stock (above-ground litter versus below-ground input) as well as bacteria controlling the rates of decomposition.

The following section is in my opinion, the most important section of the inquiry: an evaluation into how much of a difference carbon stock enhancement will actually make to the UK’s carbon footprint.

Is carbon neutrality by enhancing carbon stocks feasible?

First, we need to evaluate what such carbon stock enhancing measures do to carbon stock in an area. A study in the province of Shaanxi, China (Cui et al, 2015) [showed that] a 15 year large-scale ecological restoration project yielded a 29.3% increase in carbon stock. This study gives us a good indicator of what stock enhancement in the UK will be like: carbon stocks will improve, albeit not drastically and not hurriedly, but we will see improvements. One should note, however, that an ecological project in the UK won’t accumulate as much carbon as the province in Shaanxi, given Shaanxi is the same size as the entire UK. For the UK to become carbon neutral through afforestation alone, using data from the Forestry Commission, estimates suggest one would need to plant and maintain 50 million hectares of trees – each hectare enhancing the carbon stock by three tonnes annually. The problem with this, however, is that 50 million hectares is double the land area of the UK. Furthermore, for the UK to offset carbon emissions from just car use, we would need to afforest 75% of the UK’s land area – hence it is clear afforestation alone won’t make the UK carbon neutral.

Figure 2: GHG emissions by sector using 2018 Government statistics.

Clearly it is not feasible for the UK to become carbon neutral just enhancing carbon stock. However, I think that enhancing carbon stock can go at least 30% of the way to carbon neutrality (estimate derived from 30% increase in carbon stock over 15 year period versus carbon dioxide emissions over the same time), as small measures make a big difference, like community forestry or like organic amendments. We have to recognise that enhancing carbon stock won’t immediately make the UK carbon neutral, but, in the long term, it will yield environmental benefits (the Shaanxi case (3) highlights this). Conversion of land cover types is an incredibly effective method of restarting carbon sequestration and greatly accumulating carbon stock – like the conversion from grassland to wetland, whilst the preservation of peatlands and wetlands must be highlighted, especially Scottish peats and bogs, as it is these semi-natural land types which contain the majority of soil carbon stock, with soil in turn containing the majority of the UK’s carbon stock. In the end, to push towards the goal of carbon neutrality, we as a country need to make changes – from pushing towards a renewable-based energy grid (which in fairness is being attempted) as well as researching cleaner transport options (See Figure 2) and although this may be arduous and require a change in lifestyle, measures like these are becoming more necessary as the global climate crisis worsens.

Conclusion

In conclusion, enhancing climate stock alone won’t make the UK carbon neutral, but when done in combination with other environmental reforms, it has the potential to play a huge part in improving the UK’s environmental situation. Everyone has a role to play in allowing the UK to achieve carbon neutrality: enhancing carbon stock is a good step to fulfilling one’s role.

Ayushman 206262

 Bibliography

  1. Wilfred M. Post, R. Cesar Izaurralde, Julie D. Jastrow, Bruce A. McCarl, James E. Amonette, Vanessa L. Bailey, Philip M. Jardine, Tristram O. West, Jizhong Zhou, Enhancement of Carbon Sequestration in US Soils, BioScience, Volume 54, Issue 10, October 2004, Pages 895–908, https://doi.org/10.1641/0006-3568(2004)054[0895:EOCSIU]2.0.CO;2
  2. Ravindranath, N. H.; Murthy, Indu K.; Samantaray, Ranjan. 2012. Enhancing carbon stocks and reducing CO2 emissions in agriculture and natural resource management projects: toolkit (English). Washington, DC: World Bank. http://documents.worldbank.org/curated/en/830421468331786085/Enhancing-carbon-stocks-and-reducing-CO2-emissions-in-agriculture-and-natural-resource-management-projects-toolkit
  3. Cui, Gaoyang et al. “Temporal-Spatial Pattern of Carbon Stocks in Forest Ecosystems in Shaanxi, Northwest China.” PloS one vol. 10,9 e0137452. 9 Sep. 2015, doi:10.1371/journal.pone.0137452
  4. De Stefano, A., & Jacobson, M. G. (2018). Soil carbon sequestration in agroforestry systems: a meta-analysis. Agroforestry Systems, 92(2), 285-299. https://doi.org/10.1007/s10457-017-0147-9
  5. Warner, D. 2008. Research into the current and potential climate change mitigation impacts of environmental stewardship. Report to Defra.
  6. UK’s Carbon Footprint 1997-2016, Department for Environment, Food and Rural Affairs (DEFRA), April 2019
  7. www.communityforest.org.uk (accessed 21/02/2020)
  8. ONS: UK Natural Capital – Carbon Stock estimates, 2016

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