Role of Carbon Sequestration and its Pros and Cons You Never Knew

Explanation of carbon sequestration
Carbon sequestration can be an effective way to counter climate change. But what is carbon sequestration, and how does it work? Buzzle answers such questions, along with giving you the various pros and cons of carbon sequestration.
Did You Know?
One-third of the annual carbon dioxide released by human activities is stored in the oceans, which amounts to around 2 billion metric tons per year.
The world today is witnessing the effects of climate change. Frequent flooding, cloudbursts, hurricanes, unseasonal monsoons, and tsunamis, have got a lot to do with this phenomenon. Worldwide, fingers are being pointed at the use of fossil fuels like coal and oil, which man uses to fire his machines.

A shift to renewable energy sources is being suggested as the best course of action. However, research and statistics prove that such an immediate shift is not possible, at least for the next few years. Moreover, large electric grids, like those in America, cannot be operated solely by using renewable sources of energy.

Since the chief culprit of climate change is air pollutants like carbon dioxide, attention has been focused on getting rid of this issue. The possibility of trapping this gas from the air for prolonged periods was considered. This process is called carbon sequestration. An even simpler definition is the storage of carbon dioxide in a reservoir, other than air. When it is carried out artificially, by liquefying and storing carbon dioxide, the process is called 'Carbon Capture and Sequestration', or 'Storage' (CCS). Let us check out the various methods of carbon sequestration, along with its pros and cons.
What is Carbon Sequestration?
Carbon sequestration is a method by which carbon-rich gases are absorbed from the atmosphere, converted into other products, which then stored in plants, soil, oceans, or geological formations. This process has occurred naturally since billions of years, and in recent times humans are trying to utilize it to reduce the amount of carbon dioxide released by industrial activities.
Role of Carbon Sequestration
Carbon occurs in various forms on the planet; in the air, soil, plants and animal matter, and the oceans. In the atmosphere, it occurs in the form of greenhouse gases like carbon dioxide. These gases form an envelope around the surface of the Earth, and keep it warmer than it would otherwise be, by trapping infrared radiations, thus helping support life. This is similar to a greenhouse, in which heat is trapped inside to enhance plant growth. Carbon dioxide is released by plants and animals when they breathe and during their decomposition, as well as from soil and oceans. However, if its concentration in the atmosphere becomes excessive, it can raise the Earth's temperatures to dangerous levels.

To maintain the balance of carbon (called the carbon cycle), carbon dioxide must be absorbed from the air and stored in other forms on Earth, in 'sinks'. Natural carbon sinks are plants, soil, and oceans. However, due to increasing pollution levels, the carbon balance has been thrown off balance, leading to an excess accumulation of carbon dioxide in the air. There are fears that this may lead to climate change, by warming up the Earth. Therefore, in order to control the level of carbon dioxide and prevent climate change, more emphasis needs to be given to carbon sequestration.
Carbon Sequestration
Carbon Sequestration Methods
Natural Processes
► Plants absorb carbon dioxide from the air via pores in their leaves, called stomata, and perform photosynthesis to convert this gas into carbon, stored in their bodily tissues like roots, stems, and leaves.
► Animals which consume plants, called herbivores, transfer the stored carbon into the soil via their excreta. Plants and animals, on dying, are decomposed by soil microbes, which also release carbon. Soil carbon is stored in the form of decomposing plant and animal fragments, microbes such as nematodes, and fungi, and in the form of a mineral-carbon composite called humus.
► In peat bogs, plant matter is decomposed in the absence of air, leading to more carbon being stored in it than is released to the atmosphere. Over time, large carbon deposits form coal reserves, such as those used by man.

► Most of the carbon dioxide is sequestered in oceans by plankton and aquatic plants which absorb it via photosynthesis. When these die, they sink to the bottom and decompose, releasing carbon deposits
Artificial Processes
► Carbon sequestration can be enhanced by changing land use practices, especially the pattern of cropping, such as, by growing cover plants in the field between two seasons, or between rows of the main crop, by no-till farming, use of compost and manure, crop rotations, and slope-protection by planting trees.
► Fast-growing trees can be grown specifically for trapping carbon dioxide on barren lands. Since it's desirable that they should not release the carbon back to the atmosphere by decomposition, long-lived trees, especially those that live above 100 years, are preferred.

► Protection of existing forests, restoration of wetlands, better management of grasslands, reducing grazing, and reducing chances of forest fires can go a long way in maintaining the natural rate of carbon sequestration.
► Carbon dioxide produced in power plants can be trapped, liquified, and injected into aging oil fields, which pressurizes more oil to enter the wells, a process called Enhanced Oil Recovery (EOR). Earlier, water was injected for the same purpose.
► Liquefied carbon dioxide can be injected deep inside mineral deposits, such as magnesium and calcium silicates, so that it reacts to form solid carbonates which remains underground. This process is still in the planning stages, and would increase power plant energy consumption by 60 - 180%.
► Carbon dioxide gas can be injected deep into oceans, where the high pressure causes it to get liquefied or solidified and slowly dissolve into the water, or stay stabilized.

► Another method for ocean sequestration is to provide aquatic plankton with artificial nutrients (such as iron filings), so that they use it to perform photosynthesis, while absorbing enhanced amounts of carbon dioxide from the air.
► Burying dead trees and other organic material deep within the ground is another sequestration method to retain the carbon inside the ground, which otherwise would have been released as carbon dioxide gas after conventional decomposition.
▲ Carbon sequestration prevents climate change by removing excess amounts of carbon dioxide from the air.

▲ The gas can be easily liquefied and transported by pipelines, which makes deep injection convenient.

▲ Along with removing excess pollutants from the air, deep injection of carbon dioxide also enhances extraction of fuels like oil and methane from their deposits.
▲ Renewable energy sources like solar and wind energy are not expected to completely replace coal in the near future. Still, it may be possible to reduce emissions by 80 to 85%, using carbon sequestration, even while using fossil fuels.

▲ There are no reports yet of carbon dioxide leaking out from where it was injected, and this is unexpected to happen for 1,000 years.
▼ Carbon sequestration is a costly method, and implementing it in power plants requires 40% more coal. Moreover, the energy cost of sequestration is expected to rise by 1 to 5 cents per kilowatt hour.

▼ If the injected gas leaks out because of structural faults in the geological formation, it can be fatal. This is especially because carbon dioxide is denser than air, and would remain near the land surface.
▼ The process of trapping and liquefying carbon dioxide from power plant emissions requires significant electrical power. Already, 20% of power produced by such plants is used up during their operation itself.

▼ The high amounts of carbon dioxide injected into the ocean will turn it acidic, endangering aquatic life. The oceans are already significantly acidic, due to the increased amount of carbon dioxide levels in the air.
▼ Carbon dioxide gas from power plant emissions is too low in concentration to be liquefied efficiently.

▼ Trees planted to absorb and store carbon from the atmosphere need sufficient time to mature. Moreover, once they die, there is always the danger of carbon dioxide gas being released through decomposition.

▼ There may not be enough geological reservoirs available or accessible for sequestering carbon.
▼ Because carbon sequestration allows the use of fossil fuels, it may divert government funding from cleaner, environment-friendly technologies.
While the cons far outnumber the pros of carbon sequestration, it is wise to say that this technology should be implemented only after further research is carried out. However, till then, focus can be shifted to conserving the natural sequesters of carbon - forests.