First go through the text (given after the questions) and then attempt the questions.

QUES 1 . Which among the following is an example of  Geological sequestration-

a . Storage of CO2 underground in depleted oil and gas reservoirs.

b . Injection of CO2  to the ocean bottom and stored there.

c . Burying biomass (such as trees) directly.

d . Mineral sequestration.

Answer- a

QUES 2 . Carbon sequestration can be done through-

1 . Wetland restoration

2 . Mixing ocean layers

3 . Ocean iron fertilization

4 . Modification of agricultural practices 

5 .  Chemical scrubbers

Select the correct answer using the code given below:

a . 2 , 3 , 4 & 5

b . 1 , 3 & 4

c . 1 , 2 , 3 , 4 & 5

d . 1 , 2  & 3

Answer – c


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It is a process of carbon capture and  long-term  storage of CO2 or other forms of carbon over a long period of time. The initial purpose of doing this is to delay global warming and avoid extreme climate change.

In other words ,the process by which carbon sinks remove carbon dioxide (CO2) from the Earth’s atmosphere is called carbon sequestration.

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Sequestration processes 

Carbon dioxide (CO2) is  captured from the  atmosphere –

1 . Naturally through biological, chemical, and physical processes.

2 . Artificially through large-scale, artificial capture and sequestration of industrially produced CO2 using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks.


Biosequestration is carbon sequestration through biological processes like-

1 . Peat bogs – act as a sink for carbon due to the accumulation of partially decayed biomass that would otherwise continue to decay completely. By creating new bogs, or enhancing existing ones, the amount of carbon that is sequestered by bogs would increase.

2 . Reforestation – is the replanting of trees on marginal crop and pasture lands to incorporate carbon from atmospheric CO2 into biomass.

3 . Urban Forestry – increases the amount of carbon taken up in cities by adding new tree sites and the sequestration of carbon occurs over the lifetime of the tree.

4 . Wetland restoration – Wetland soil is an important carbon sink; 14.5% of the world’s soil carbon is found in wetlands, while only 6% of the world’s land is composed of wetlands.

5 . Modification of agricultural practices – is a recognized method of carbon sequestration as soil can act as an effective carbon sink offsetting as much as 20% of  carbon dioxide emissions annually.

6 . Ocean iron fertilization –  Iron fertilization attempts to encourage phytoplankton growth, which removes carbon from the atmosphere for at least a period of time.

7 . Urea fertilization –  fertilizing the ocean with urea, a nitrogen rich substance, to encourage phytoplankton growth.

8 . Mixing ocean layers – mixing may be achieved by placing large vertical pipes in the oceans to pump nutrient rich water to the surface, triggering blooms of algae, which store carbon when they grow.

9 . Growing seaweed –  Seaweed grows very fast and can be harvested and processed to generate biomethane, via Anaerobic Digestion to generate electricity and thus reduce demand for fossil fuel energy.

  Physical Sequestration

1 .Bio energy with carbon capture and storage (BECCS) –  BECCS refers to biomass in power stations and boilers that use carbon capture and storage.

2 . Burial – Burying biomass (such as trees) directly, mimics the natural processes that created fossil fuels. Landfills also represent a physical method of sequestration.

3 . Ocean storage –  CO2  may be  injected to the ocean bottom and stored there.

4 . Geological sequestration – refers to the storage of CO2 underground in depleted oil and gas reservoirs, saline formations, or deep, un-minable coal beds.

Chemical Sequestration

1 .  Mineral sequestration – Carbon, in the form of CO2 can be removed from the atmosphere by chemical processes, and stored in stable carbonate mineral forms. This process is known as ‘carbon sequestration by mineral carbonation’ or mineral sequestration.

2 .Chemical scrubbers –  Various carbon dioxide scrubbing processes have been proposed to remove CO2 from the air.

3 . Basalt storage – Carbon dioxide sequestration in basalt involves the injecting of CO2 into deep-sea formations. The CO2 first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of Ca2+ and Mg2+ ions forming stable carbonate minerals.

4 . Neutralisation of ocean acidification – Carbon dioxide forms carbonic acid when dissolved in water, so ocean acidification is a significant consequence of elevated carbon dioxide levels, and limits the rate at which it can be absorbed into the ocean. A variety of different bases(limestone ,  sodium hydroxide , etc)   have been suggested that could neutralize the acid and thus increase CO2 absorption.


Though promising these techniques are not free from limitations such as-

1 . When carbon dioxide is stored deep underground at depth, hydrostatic pressure acts to keep it in a liquid state. Reservoir design faults, rock fissures and tectonic processes may act to release the gas stored into the ocean or atmosphere.

2 . Huge financial costs is associated with these technologies. This will be a burden especially on the developing countries.

3 . The energy requirements of sequestration processes may be significant.