It's exactly what it sounds like, just as artificial trees was the implementation of tree-imitating devices, afforestation is the planting of trees in previously non-forested places to create a net carbon sink and storage of carbon (Haszeldine & Scott, 2014), and is one of the biggest terrestrial geoengineering schemes proposed to date. The IPCC Fifth Assessment Report assumes that CDR afforestation will be used in the future as a geoengineering strategy (Bellamy et al. 2012). Large-scale afforestation has the capability to counterbalance carbon absorption with anthropogenic carbon emissions from industrialisation, through photosynthesis and increased biomass (Zhang et al. 2014). In fact, it has been suggested that afforestation in non-forested and urban areas could result in carbon storage of approximately 12% of current carbon emissions by 2015 (Andelin et al. 1991).
From the outset it sounds like the idea is simple, deforestation has resulted in increased atmospheric carbon dioxide concentrations, so surely in an attempt to prevent this, we should plant more trees!
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Wrong.
If this were the case, the geoengineering scheme would be reforestation, yet afforestation requires previously non-forested land. Proposals first considered afforestation schemes to take place in temperate high latitudes, but research suggested that barren land has a higher albedo for an increasing cooling effect (Manfready, 2011). Ergo, afforestation proposals have been considered for desert environments.
Geoengineering projects have been initiated in China, the Sahara and Australia alike. In desert conditions, fast growing trees are preferred- particularly eucalyptus, as plantations of 1000 eucalyptus trees have the capability to sequester ~0.5-1 x 104 kgC/hayr (Zhang et al. 2014).
Large-scale desert afforestation was launched in China in 1978 as the 'Great Green Wall Plan' to vegetate the north-western, north eastern and north provinces of China (Veste et al. 2006). The 'wall' would be made up of tree shelterbelts, which are a protective forest system designed to conserve soil and water supplies. The Three Norths Shelterbelt is part of the 'Great Green Wall' and is 4480km long, and between 400 and 1700km wide, and covers 42% of China's territory (Veste et al. 2006). In China, afforestation is increasing carbon storage within the biosphere between rates of 30 to 74g/m2yr. Success!
Similarly, Orsntein et al. (2009) has gone so far to suggest that the combined afforestation of the Australian outback and Sahara desert could offset all carbon dioxide emissions resulting from fossil fuel burning. It has also been noted that afforestation succeeds on previously degraded land. For example, in India, Jatropha plantations on marginalised land can add 1450kgC/ha/yr to the soil as 4000kg of plant biomass (Zhang et al. 2014). This illustrates that afforestation schemes do not require greenfield sites and clean land to develop areas of forestry, and could greatly improve and flourish previously degraded land. Afforestation schemes, particularly in desert areas could also contribute socio-economically to local communities for agricultural and timber purposes.
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However, there are side effects to vegetating deserts, including an induced increase in ability to carry more avian diseases, which if prevalent in the Sahara, would impose risks to Sub-Sharan regions and mainland Europe (Manfready, 2011).
Research also suggests that large-scale afforestation activity can cause a decrease in local surface albedo, and an increase in air temperatures in neighbouring areas. The consequence of this action is that afforestation could be inducing more global warming than that that would ensue if geoengineered afforestation did not take place. Similarly, although afforestation can be praised for being almost 'risk-free' and highly feasible in comparison to other significant geoengineering proposals, the process is extremely slow, and therefore a less effective method (Keith, 2000). My previous post regarding artificial trees was proposed due to the slow rate of natural photosynthesis, therefore, simply planting trees to sequester atmospheric carbon is a slow process regardless of the amount of trees planted. This similarly means that should we be on the onset of reaching a climate tipping point, afforestation is not an emergency response to saving the climate and environment as we know it. The process is not rapid, and could not prevent significant climate changes, and ultimately the forested trees are likely to be subject to changes derived from the climate tipping point (Andelin et al. 1991).
Another caveat to this solution is the eventual re-release of carbon back into the atmosphere. Although trees have the ability to store carbon for years on end, carbon returns to the atmosphere in the tree's eventual death, through natural decomposition, or during tree harvesting (Andelin et al. 1991). Therefore, in order to capture carbon at a constant rate, trees would have to be disposed of and continuously replaced, and fertilisation would be required to re-enrich trees with the required nutrients, which is a highly intensive process which would require regular maintenance (Keith, 2000), and who would be willing to provide that? Would it be up to the host country to provide maintenance?
Afforestation does have potential, and despite a few associated risks, it is definitely a worthy geoengineering strategy but can it really produce effective and efficient reductions in carbon emissions? The process is almost too lengthy, and requires a large land area to produce any significant effects.
If areal extent and tree maintenance were not potential social problems, and the rate of photosynthesis was not as slow as it appears to have been suggested, afforestation could be the answer to our climate change problems. However, afforestation cannot compete with the rapid climate changes which comprise our future!
All in all, it appears that carbon reduction methods are subject to success and failure, and have an incredible impact on global environmental change- but can they save our planet?
Find out next time!
S xx
Really interesting stuff! In your opinion, would you say the benefits of afforestation outweigh the negatives? Surely the issue of carbon eventually being released would be the case with any other, more high risk geo-engineering strategy, as eventually something is bound to give? Pity such large areas of land are needed for this approach...What would you say the most appropriate strategy so far is?
ReplyDeleteHi Celia, my opinion towards afforestation is that it is unique compared to other geoengineering options in the fact that it relies on purely natural processes- eg. photosynthesis. It doesn't require combustion of natural products, or artificial replicas, and it isn't an attempt to meddle with ocean dynamics, afforestation is just the planting of new trees. Despite this, I would foresee some conflict regarding land space, land use, which is already prevalent with debate over food security and biofuel production. The argument there then, is whether we should put more pressure on land use change when there are other carbon reduction methods out there? I think that afforestation benefits outweigh the negatives is on a small scale however, not as a geoengineering scheme, as on a global scale it neither has a quick rate of carbon absorption, and runs the risk of re-release of atmospheric carbon.
ReplyDeleteThe issue of re-release of carbon into the atmosphere is very dependent on the geoengineering method proposed. For example, those schemes which utilise the deep ocean, carbon can be stored for millions of years before re-release, whereas afforestation, re-release occurs when a tree dies, or is cut down in deforestation, the ease of releasing carbon back into the atmosphere is greater. The issue with the ocean is not re-release but whether we could be pushing its capacity limits as a carbon store.
Similarly, solar radiation geoengineering reduces incoming solar radiation, and does not impact upon the carbon levels, within any of the Earth's carbon sink, therefore not impacting upon a carbon reservoir's susceptibility to release of carbon into the atmosphere.
So far in my personal opinion alone, I think that a large number of the proposals have been successful on a small scale, and would actually think that a combination of these proposals on a smaller scale would perhaps be more appropriate than a large scale, global scheme. As of yet, it seems as though the unknown is a looming concern, so proposing deployment on a large scale is too risky. I cannot choose an appropriate geoengineering strategy, but think a large effort on a small scale of a combination of techniques has the potential to be more beneficial, and could be researched further!