Carbon Dioxide Capture- An overview (Part 1)

This week’s blog diverts to a new type of geoengineering process, carbon dioxide removal.  Carbon Dioxide Removal (CDR) focuses on artificial ways of reducing carbon dioxide levels from the atmosphere.  This blog aims to focus on one CDR process, known as Carbon Dioxide Capture (CDC).   

CDC absorbs carbon dioxide from the air, through an industrial process.  Large power plants with a high level of thermodynamics are essential to capture carbon dioxide (The Royal Society 2009).  Once this carbon dioxide is captured it can either be stored or used for energy.   It is generally hard to capture carbon dioxide from the atmosphere as it composes of 0.04% of the air (The Royal Society 2009). Furthermore, large amounts of energy may also be required to collect carbon dioxide from the air, leading to high costs.  

 In general, there are three main ways to capture carbon dioxide from the atmosphere. However, all three processes have only been analysed at a laboratory scale. 

Absorption of carbon dioxide on solids

Firstly, Lackner (2009) suggests the creation of large filters (sorbents).  These filters allow air to pass through, and capture CO₂.  This process is also referred to as absorption on solids and is considered a fairly safe process with no risks on the environment or people.  However, as time passes the sorbent will hold higher amounts of CO₂, decreasing the amount of absorption occurring and decreasing the filter efficiency.  Further information about Lackner’s proposal will be analysed in more detail in my next blog. 

Highly Alkaline Solutions absorbing CO₂

Secondly, another way to absorb carbon dioxide is through highly alkaline solutions.  Solutions of high alkalinity cause high kinetic reactions, absorbing CO₂.  This process has been suggested to be undertaken using Sodium Hydroxide spray.  However, it is suggested that a reduction of CO₂ by 30% would also decrease the moisture in the atmosphere (Stolaroff et al 2008).  For every molecule of carbon dioxide being captured, 30 molecules of water vapour would also be captured (30mol-H2O per mol-CO₂), hence decreasing the atmospheric moisture substantially (Stolaroff et al 2008).  Consequently, as the air moisture decreases, this may have negative impacts on the frequency and intensity of rainfall leading to negative effects on the hydrological cycle (Stolaroff et al 2008).  Therefore, this may increase the amount of floods or droughts occurring, leading to catastrophic impacts on agriculture, decreasing food and economic security.

Moderate Alkaline Solutions with a Catalyst to absorb CO₂

Lastly, another way to capture carbon dioxide is through using a moderate alkaline solution with a catalyst.  This process is similar to Stolaroff et al’s suggestion.  Yet, the catalyst increases the reaction rate of the alkaline solution with the atmosphere, hence absorbing carbon dioxide (Bao and Trachtenber 2006).  However, it is essential to acknowledge that water vapour will also be absorbed with this process.  Thus, again affecting air moisture and the hydrological cycle.

CDC Evaluation

Although CDC may reduce carbon dioxide emissions at a fast and efficient rate, a lot of energy is essential. High levels of electricity will be required for CDC to take place (Haszeldine 2009).   Hence, providing electricity by burning fossil fuels should be avoided. Therefore, a renewable energy like wind power or solar power will be required for this process to take place without any CO₂ emissions (Lackner 2009). The Royal Society (2009) suggests that this process may be relatively expensive.  Nonetheless, in the long run when accounting all the carbon dioxide emission reduction, it may be worthwhile. 

Additionally, another problem with CDC is the disposal.  It has been suggested to store it in a secured location, such as near oil or gas fields.   This may be problematic as transport costs will occur and a large storage space will be required in the long run (The Royal Society 2009).  However, a more productive alternative may be to re-use this carbon dioxide.  It has been suggested to combine CO₂ with hydrogen and convert it into a transport fuel (Lackner 2009).  For this to be achieved, CDC costs will increase substantially (Table 1).   However in the future, this may be a viable process, as costs may decrease with increasing technological advancement (Figure 1).

Table 1: CDC Summary Evaluation
Source: The Royal Society 2009

Figure 1: CDC as time passes- the more time passes the more cost efficient it becomes
Source: Haszeldine 2009 

Thoughts:

Provided that CDC becomes technologically efficient and relatively cheap, it could be successful.  Nonetheless, Stolaroffs and Bao & Trachentnber processes may not be as desirable due to the impacts on the atmospheric moisture.  Therefore, its success is questionable as it may also cause a lot of hydrological damage rather than reduce climate change impacts.  Controversially, Lackner’s process has no environmental or hydrological impacts and it seems to be a very safe process with less risks.  I believe this could be a viable solution to decreasing carbon dioxide levels.  Follow me next week where I will analyse two examples of CDC processes; artificial trees (Lackner) and a porous liquid (Zhang et al.).  But for now, please let me know your thoughts on the matter.

SRM Poll!

To all my readers, I would like to start with a big THANK YOU.  Thank you, for your interest and participation on my geoengineering analysis.  I hope this has intrigued you and made you consider geoengineering as a solution to mitigate climate change impacts.  I hope you have enjoyed the journey until now. 

In my next blogs I have decided to move away from SRM processes and begin to analyse Carbon Dioxide Removal (CDR) as a geoengineering process. 

However, before doing so, I would be ever so grateful if you could take part in a quick poll.  This poll regards your opinion on the SRM processes presented.  I have also added an  ‘Other-Please Comment’ option if you think any other SRM process may be effective which I have not included.  If so please let me know.  Also if you wish, please feel free to add a reason on why you chose a specific answer, it would be much appreciated!

 It would be of great help as I aim to work on a post in the near future regarding your opinions on geoengineering.  It would also be amazing to know if I have changed your opinions in any way.

I have added some illustrations I thought were entertaining relating to SRM processes.  I hope they jolt your mind!

Comic source regarding geoengineering SRM processes
Source: Code Green

Humans trying to hide the Sun, indicated through a large nuclear gun- suggesting a chemical change in the atmosphere through SRM processes
Source: Climateviewer

Marine Cloud Brightening

This week’s blog aims to assess another SRM process, the marine cloud brightening (MCB), first suggested by Latham (2002).  This process aims to add small particles of seawater vapour in the atmosphere.  In 2010, Bill Gates decided to expand his cloud building from Microsoft applications to the real world!  He donated $300,000 to the Silver Lining to develop machines able to convert seawater to very small vapour particles.  These particles will be sprayed in the atmosphere, to form stratocumulus white clouds, outlining the main MCB principle (Morton 2009).   Researchers suggest ships to distribute these particles in the atmosphere using Flettner rotors, rather than a conventional diesel engine (Latham et al 2012).  A Flettner rotor is a vertical cylinder that rotates to provide electricity, hence creating movement in these ships that would spread the seawater vapour in the atmosphere to form these white clouds (Figure 1).  Therefore, once these white clouds are formed, less solar reflection reaches the Earth’s surface, creating cooler climate conditions.

 

Figure 1: Illustration of Marine Cloud Brightening with Flattener rotors
Source: Latham et al 2012

 The MCB process, is nicely described by the researchers, using the following video:

Effectiveness and world Impacts

It is expected precipitation rates will decrease in some areas of the world.  This will be disadvantageous in areas highly dependent on water for agriculture.  It is expected that the precipitation in South America will decrease by 50% (Latham et al 2012).  Thus, the Amazonian region will face a decline in rainfall, drastically influencing the Amazon rainforest.  A decline in rainfall could substantially decrease this rich tropical ecosystem, deteriorating biodiversity (Figure 2).  Nonetheless, it is important to acknowledge that dry areas which are expected to suffer the most from climate change, such as Africa and India may benefit with increasing precipitation (Jones et al 2009).

Figure 2: Land Precipitation and Vegetation approximations from 2030-2059
Source: Modified figures from Jones et al 2009

The above deductions were made using the Hadley Centre Global Environment Model Version 2, (HadGEM2).  However, Rasch et al (2006) uses the Community Climate System Model (CCSM) and suggests no changes in rainfall globally.  This difference in the two models may have occurred due to two reasons.  Firstly, this difference may be due to Rasch et al (2006) seeding a larger amount of the ocean compared to the HadGEM2 model.  Secondly, this difference may occur, as each model takes into account different factors and simulates the Earth in a different way. Hence, making this observation highly variable to model discrepancies and highlighting the uncertainties of theoretical assumptions.

 Another negative impact is that cooling in MCB is non-uniform and occurs regionally.  There is significant warming  which occurs mostly in high latitudes.  However, the lower latitudes have a decreased temperature (Jones et al 2011).  Therefore, it is questionable to what degree the MCB process is globally effective.

Furthermore both models (HadGEM2 and CCSM) show sea ice melting will decrease during the summer months and sea ice thickness will increase near the polar regions in the Northern Hemisphere (Latham et al 2012).  They also expected that sea-ice will increase by 0.9 and 0.5 million km² in the Arctic and Antarctic regions respectively (Jones et al 2011).  Therefore, due to the ice not melting, there is a declining rate of sea-level rise.

Thoughts

I believe the MCB process may have less negative environmental impacts than the artificial aerosols.  It may also seem more plausible than the space mirrors although it may not be as safe as white/green/PV roofs it may be more effective.  The MCB process once applied, can delay global warming for approximately 25 years, thus reducing temperatures to levels 25 years ago (Jones et al 2009).  However, as the Silver Lining research group suggests, this process should be used to delay climate change impacts, to give some breathing space to develop renewable energy and also reduce carbon dioxide levels in the atmosphere.  The MCB may be very effective and has been highly discussed.  However, I am unsure if this is a correct approach.  As population rates are continuously increasing, they become highly dependent on water as a source of hygiene and sustenance of crop growth.  Hence, a decrease or a shift in the amount of rainfall in specific areas may lead to political tension between nations that may share a water source.  Despite these negative implications, MCB will be seriously considered by all nations taking part in the United Nations Framework Convention on Climate Change (UNFCCC), which will occur in Paris (COP21).  Have we come to the point where such drastic changes are essential to reduce climate change impacts and each country is incapable of reducing their own emissions? Do you believe it is a viable process?

'Colouring' roofs

Today I would like to discuss with you 3 main types of roofs: the typical white roof, the green roof and the PV roof.  Keep on reading to find out more…

With a rapidly increasing population, and a rise in global economies, urbanisation is expanding. This increases the amount of roads and buildings, creating dark surfaces that reduce solar reflection and the Earth’s albedo.

A geoengineering method that could enlarge albedo reflectance is through painting roofs and human settlements white, bringing about a net increase in albedo of 0.1 in urban areas (The Royal Society 2009). The increase in albedo increases solar reflectance and reduces global temperatures.  This may lead to a decreasing rate of glacial ice melting and less of an impact on the environment.  Although this geoengineering process may take a few decades to be implemented worldwide, once complete, effectiveness should be highly apparent (Table 1). Furthermore, there are very low risks with the white roof method compared to other SRM processes.

 

Table 1: White Roof Evaluation Summary
Source: The Royal Society 2009

Criticism of White Roofs

Jacobson and Hoeve (2011) may disagree suggesting that local temperatures will decrease by 0.02K, however, global temperatures will increase by approximately 0.07K.  The white roofs reduce temperatures near the surface air.  However, there is a reduced sensible heat flux (i.e. heat energy transferred from the Earth’s surface to the upper atmosphere).  Consequently, due to a reduction in the sensible heat flux, cold air cannot be transported further up in the atmosphere, hence leading to a local cooling but a global warming.

Furthermore white roofs are accumulated in specific areas, causing small changes in cloud optical depths and winds.  Therefore, clouds intensify over the northern hemisphere making the area cooler and increasing surface albedo.  However in the Southern Hemisphere, temperatures increase, causing global temperatures to rise.  Hence there will be less clouds in the Southern Hemisphere leading to a decrease in precipitation events such as snow and rain (Jacobson and Hoeve 2011).   Consequently the hydrological cycle may be negatively impacted in the southern latitude.

Another disadvantage is that a high amount of carbon dioxide aerosols in the atmosphere absorb upward solar radiation from the reflection of white roofs and trap heat within the atmosphere, increasing global temperatures (Jacobson and Hoene 2011).

Lastly, white roof reflections are effective in warm areas, this causes energy efficiency when using electrical cooling appliances, saving energy (Cubi et al 2015).  However, if an area is cold and becomes cooler due to an intensification in surface albedo, such as Canada, this increases energy demand and more fossil fuels need to be burnt for electricity.  It is suggested that cold areas would consume more electricity than in warm areas, therefore increasing carbon dioxide in the atmosphere (Jacobson and Hoeve 2011).

An alternative suggestion

Cubi et al 2015 suggests an alternative method in cold climates; green roofs and Photovoltaic (PV) roofs.  Green roofs (or eco-roofs) are vegetated roofs, where organic material is grown.  This is aesthetically appealing, can create sound and heat insulation and can be a good way in preserving habitats.  Although the reflectance will be less compared to white roofs, there may be some reduction in carbon dioxide due to photosynthesis of plants.  Furthermore little maintenance is required and less heat will be needed for buildings in cold environments.  The PV roofs are photovoltaic panels placed on the roof of buildings, creating renewable energy with no carbon emissions, reflecting some solar energy and decreasing environmental impacts.  However, PV roofs, would not be sufficient during cloudy days with no sunlight for energy (Cubi et al 2015). 

Consequently, PV roofs are preferred overall, as it is the highest performing amongst all categories (Table 2).  PV roofs reduce carbon dioxide levels and save energy to a higher degree compared to any other type of roof. However, it may be argued that Green roofs are cheaper and a longer lasting method which also conserves environmental habitats to some degree.  Furthermore white roofs have significant negative impacts on ecosystems.  When modelling the white roofs process, it is suggested that the expected outcome will not be achieved, as global temperatures will increase rather than decrease.

 

Table 2: A summary of the 3 types of roof reflectance
Source: Cubi et al 2015

Thoughts

I think PV roofs would be the most beneficial in terms of reducing carbon dioxide emissions and declining climate change impacts.  Even though green roofs cannot be disregarded due to their many advantages.  In general, PV roofs and green roofs could be a success and a safe, cost-effective process.  I believe this may be the first indication of alternative small-scale geoengineering that could be successful in the long term, reduce global carbon dioxide emissions and global temperatures without many (or any) risks.  What do you think?