Trees, trees, trees!

From artificial trees to real trees... Let's move on to our penultimate form of CDR methods, let's talk about Afforestation.

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!

Source: Oecotextiles

Simple right?

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.

Source: ClipArt

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

Pure and simple?

The main problem surrounding climate change is our anthropogenic influence on atmospheric carbon concentrations. Human activity has enhanced carbon dioxide emissions from pre-industrial times (~1750) of 260-270 ppm (Wigley, 1983) to 395.93ppm today (Co2now, 2014. The geoengineering schemes that we have discussed so far have focused on carbon dioxide removal from the atmosphere via a plethora of methods and avenues, from enhancing weathering processes, foresting land and adding nutrients to the oceans, but why not find a direct method to remove carbon from the atmosphere? Why not undergo air purification?

Since 2009, the idea proposed by Lackner was to manufacture 'artificial trees' to capture carbon from the atmosphere. The design can be seen below.

Source: geoengineering2012

The trees are able to mimic the planet's natural uptake of carbon dioxide, as the prongs contain sodium hydroxide, which acts to chemically consume carbon dioxide and transform sodium hydroxide (lye) into sodium carbonate (Biello, 2009). The carbon dioxide is then heated at 900 degrees celsius, releasing the carbon dioxide to enable sodium hydroxide to re-react with atmospheric carbon dioxide once more. The artificial tree is able to remove carbon dioxide from the atmosphere at a  much faster rate than natural photosynthesis (Schiffman, 2013), and scientists have envisaged the existence of forests of these artificial trees to optimise carbon removal.

The idea has been supported by both the UK Royal Society and the Institution of Mechanical Engineers as the safest and most effective geoengineering technology suggested. However many statistics from 2009, when the advent of this proposed solution occurred, implied that these artificial trees would be demonstrated in society by at least 2014, which of course is today. Has anybody witnessed any demonstration of artificial trees yet?

The Institution of Mechanical Engineers actually believed that post-demonstration in 2014, a full scale 'forest' of artificial trees could be implemented by 2018, and global deployment by 2040 (Biello, 2009). The questions have to be asked: Why has this not happened? What has hindered the project's progress?

The hindrance could be a result of a multitude of reasons. Firstly, the concept sounds appealing: carbon dioxide is removed from the atmosphere using successful and efficient devices, yet where does this captured carbon go? The carbon inventory proposed was underground, and some geological formations have been tried and tested, for example Basalt, as it has the ability to absorb carbon dioxide over decadal timescales to produce minerals (Biello, 2009). However there have been many caveats concerned with underground sequestration. For example, how will it impact groundwater supplies? Is there potential for carbon leakage back into the atmosphere?

Other problems with air purification are dominantly economical. The project requires large land area, production of electricity and manufacture and installation, which will all come at a huge economical expense. It has been proposed that 10 million artificial trees would be required to reduce ~12% of anthropogenic carbon emissions per year (Schiffman, 2013), ergo making a colossal change in carbon reduction to pre-industrial levels would require a huge volume of air purification devices across the globe. Similarly each artificial tree is estimated to cost $24,000, therefore even 100,000 trees is already $2.4 trillion in expenses. Can we afford this?

In response to these caveats, and the Institution of Mechanical Engineers' proposals in 2009 for air purification to be ready for deployment and installation during 2014, I found it extremely difficult to find any recent academic papers evaluating artificial trees (mitigating those of course that were in reference to artificial Christmas trees, the latter end of November was probably not the best time to look!) or air purification. In fact, the academic scene is quite muted on the subject- does this mean that this proposed 'safest and most effective geoengineering scheme' is not as hopeful as first thought?

Source: Cartoon Movement

Similarly I think that the theory does have huge potential, however, finding suitable land areas to deploy the trees globally will undoubtedly be a struggle. People are already adverse to the sight of windfarms, despite their benefits of clean, renewable energy, due to aesthetics and impact on house prices, so it is highly unlikely that they would take to having artificial trees implanted in their back garden.

How do you think this project compares to the schemes proposed so far?

S xx

Enhanced Weathering... Weather away!

Now this post will no doubt sound familiar.. Enhanced weathering? Wasn't that essentially the process behind ocean liming?

Yes, yes it was. However, this process is not confined to the oceans, but also to the biosphere.

Over millions of years rocks are worn away by rain, forming carbonates due to the slightly acidic nature of rain, as a result of its uptake of carbon dioxide. The alkaline carbonate formation, (usually calcium carbonate) is therefore induced by this chemical weathering process, and eventually washes down into the sea (Hamilton, 2013).

Source: Rgbstock

This background theory of the process of chemical weathering has been applied as a potential geoengineering scheme to reduce atmospheric carbon dioxide concentrations. Chemical weathering locks up carbon dioxide through chemical reactions between the rock minerals and air. The optimum material for enhanced weathering is Forsterite (magnesium olivine), due to it's high abundance and reactivity (Hartmann et al. 2013). An example of olivine (magnesium iron silicate) weathering with water and carbon dioxide is represented by the equation below, which results in magnesium carbonate and silicic acid, storing carbon in the process:

Schuiling et al. (2011) reviewed the above equation investigated by Kohler et al. (2010) which suggests that dissolution of 1 mole of Olivine can sequester 4 moles of carbon dioxide. This is through the consumption of carbon dioxide and the release of cations, in this case, Mg2+ into the solution. Enhanced weathering would use the natural process occurring above, but increase the surface area of rock for weathering, or increase temperature and pressure to influence ocean pH.

The process is rather advantageous. Ultimately it would help remove atmospheric carbon dioxide by accelerating natural geological processes transferring carbon and trace elements between the atmosphere, biosphere, and eventually the oceans, which is the aim of any geoengineering scheme. However, it also reduces ocean acidification- a variable caused by climate change, and induces the transferral of trace elements including phosphorous, silicon and potassium (Hartmann et al. 2013), which in turn, enhances biological productivity within the oceans, increasing photosynthesis and carbon dioxide uptake.

However, to uptake maximum carbon, theoretically the rock would have to be crushed, yet in practice, natural rock weathering is an extremely lengthy process, and ideas of quantity and volume of rock are unknown to be able to mitigate the high anthropogenic and atmospheric carbon concentrations. Similarly, should Olivine be prevalently used, it contains toxic metals including nickel that could accumulate within the biosphere, and in attempting to also reduce ocean acidification via this method, could result in higher alkalinity levels to which some marine organisms are not acclimatised (Cressey, 2014).

Enhanced weathering is therefore subject to the same flaws or uncertainties as the proposals discussed previously within this blog. Nothing has ever been induced in the large-scale, so some effects will always be unknown. Similarly, attempts at accelerating natural processes cannot guarantee emergency response to increasing carbon dioxide emissions, and combined with lack of human understanding, projects are no where near ready for installation.

Will we find an appropriate geoengineering method to solve our climate problems? Luckily proposed schemes are not limited to those discussed in this blog so far, stay tuned for more geoengineering projects! Next time- air purification!

S xx

Liming in South Australia

A corresponding case study to ocean liming is with a company called Cquestrate, who proposed an ocean liming scheme in the Nullarbor Plain of South Australia. Tim Kruger is the founder of this company, and aims to reutilise liming in a means to protect the environment from increasing global warming effects.

Nullarbor Plain is feasible for potential liming activity due to the abundance of limestone (over 200,000 km2), approximately 20MJ per m2 of daily solar radiation and only 200-300mm of rainfall per year (Cquestrate, 2008).

According to calculations, the Plain contains 10,000km3 of limestone, of which, only 5% consumption would return the 305GtC of carbon dioxide emitted between 1750-2003 back to pre-industrial levels (Cquestrate, 2008)!

Ideal!

Source: Bbm Live

This project however has been questioned with regards to using 'dirty energy' such as coal power to undergo calcination, but Cquestrate aim to use 'stranded renewable energy'. For example, according to Kurokawa (2003) deserts are untapped resources which could utilise solar radiation through photovoltaic power generation schemes. As this is never used on a large scale, it is a cheap energy source and great in the right location. This reasoning is why Australia's Nullarbor plain has been chosen by Cquestrate, as it receives ample sunlight, and is abundant in limestone material (Sandstone, 2007).

Source: Mike on bike

It would appear from the statistics that liming of the ocean could be the technological approach needed to stall the effects of current global warming, especially if the dirty energy solution can be solved, and could be applied in the large scale, as that is what the definition of geoengineering requires to take place. Also, despite the attributes listed by Cquestrate, there has been no mention of timescale, and how long it would take to reap the benefits of their project.

Who knows, Cquestrate could become future geoengineering giants (subject to project success)- watch this space!

S xx

Liming the oceans

It's time to move onto Carbon Dioxide Removal (CDR) geoengineering: Part Two.

This time the focus again revolves around the oceans, this time: Liming the oceans.

This method mirrors that of my previous post on ocean iron fertilisation, as both methods focus on utilising the ocean's ability to store copious amounts of carbon; a storage greater than any other carbon sink on the planet.

Source: wattsupwiththat

Yet, ocean liming differs from ocean iron fertilisation as it is a chemical geoengineering process using chemical reactions to increase ocean carbon storage capacity whereas iron fertilisation used biological means of enhancing carbon dioxide removal from the atmosphere. Liming was first suggested by Haroon Kheshgi, and it is the sprinkling of lime (otherwise known as Calcium Oxide (CaO)) into the ocean as a means (according to Renforth et al. 2013) of manipulating the carbonate system through the addition of CaO to improve net sequestration of atmospheric carbon into the deep ocean.

Here follows a key background of why and how liming works...

So as established in my previous post, colder waters are more optimal than warmer waters at absorbing greater volumes of carbon dioxide concentrations. Yes? Right, however anthropogenic activity in recent years has both increased carbon dioxide emissions to the atmosphere and induced a decrease in ocean pH by 0.1 units. Continuation of this pattern of behaviour could result in a 0.4 unit pH decrease over the next 100 years (Renforth et al. 2013) resulting in....

Acidification of ocean surface waters.

The climatic impacts of ocean acidification results in biodiversity loss as microorganisms such as phytoplankton within the surface waters cannot form strong shells, which is crucial as these microorganisms are greatly responsible for carbon dioxide uptake via photosynthesis.

Source: Just only

How does liming stop this?

Liming is the addition of calcium oxide, an alkaline compound. By sprinkling this compound into the oceans, it increases the oceans pH to mitigate acidification, and optimise carbon dioxide uptake. When proposed by Keshgi, hydroxide particles were added to the ocean incurring the following dissolution reactions to take place:

CaCO_3 --> CaO + CO2
CaO + 2CO₂ + H₂O --> Ca²⁺ + 2HCO₃^-

On addition to seawater, calcium oxide reacts with carbon dioxide to produce calcium bicarbonate solution. The net effect of this series of reactions is beneficial in terms of carbon sequestration as 1 mole of calcium oxide absorbs 2 moles of dilute carbon dioxide, and the production of calcium oxide only required 1 mole of pure carbon dioxide for formation (Cquestrate, 2008).

The prevalence of limestone (CaCO3) making up 10% of the Earth's land surface, makes it an ideal and abundant material to use, especially as projected input into the ocean on a global scale should only subject a minor change in ocean chemistry which suggests minimal impact on the environment.

This all sounds good, but what if too much alkalinity is added to the ocean? What happens then?

Upon initial addition of lime into the ocean, a localised elevation in pH around the point of addition is induced, which in small increments has little environmental impact, however over an increased period of time, higher pH levels are detrimental to some living organisms, and could result in carbonate precipitation, which hinders the effect of ocean liming (Renforth et al. 2013).

Also, research has discovered that the benefit of liming derived from limestone could take decades before it takes effect due to the slow process of deep ocean upwelling, and is therefore unlikely to be an emergency response to global warming. If 4 billion tonnes of powdered limestone was added to the water yearly from 2020 onwards, 1 billion tonnes of carbon dioxide could be taken up by the oceans, reducing atmospheric concentrations by 30 parts per million by 2200 (Hamilton, 2013). But can we wait this long?

The extraction of lime from limestone is both costly and emits carbon dioxide through the process, (which requires coal power)- so why not forget liming and just concentrate on reducing use of coal power plants to prevent pollution of carbon dioxide in the first place? Unless lime can be extracted using renewable energy, the scheme surely is not worth the pollution and costs of producing lime in the first place.

Similar ethical questions can be raised such as, who owns rights to the ocean? Should anyone be allowed to experiment with the ocean's chemistry? Can we account for unexpected changes?

With all of this in consideration, should it go ahead? I think as proposed geoengineering schemes go, this one makes sense, as it utilises the abundance and renewal of limestone and has little known impact on biological life. However, until this process can be derived from alternative, carbon-free means, and there is a way to increase the rate of progress, the proposal still requires considerable development.

Any thoughts?
See you next time!


S xx