Consider the following activities: 

1. Spreading finely ground basalt rock on farmlands extensively 

2. Increasing the alkalinity of oceans by adding lime. 

3. Capturing carbon dioxide released by various industries and pumping it into abandoned subterranean mines in the form of carbonated waters. 

How many of the above activities are often considered and discussed for carbon capture and sequestration? 

(a) Only one 

(b) Only two 

(c) All three 

(d) None

15.Ans: c                                                             

Explanation:

Atmospheric enrichment of GreenHouse Gas can be moderated by either reducing anthropogenic emissions, or sequestering C in plant biomass or the soil or Oceans . Transfer of atmospheric CO2 into other pools with a longer Mean residence time (MRT), in such a manner that it is not re-emitted into the atmosphere in the near future, is called sequestration. Carbon dioxide is the most commonly produced greenhouse gas. 

Depending on the processes and technological innovations, there are three main types of C sequestration : (i) those based on the natural process of photosynthesis and conversion of atmospheric CO2 into biomass, soil organic matter or humus and other components of the terrestrial biosphere; (ii) those involving engineering techniques; and (iii) those involving chemical transformations 

Geologic carbon sequestration is the process of storing carbon dioxide (CO2) in underground geologic formations. The CO2 is usually pressurized until it becomes a liquid, and then it is injected into porous rock formations in geologic basins.

Biologic carbon sequestration refers to storage of atmospheric carbon in vegetation, soils, woody products, and aquatic environments. 

Carbon sequestration techniques

Enhanced rock weathering (ERW) 

Involves spreading finely crushed basalt, a natural volcanic rock, on fields to boost the soil’s ability to extract CO2 from the air.

Crushed basalt is applied to farmland due to its benefits for soil fertility, soil biology, crop yield and health. This mineral-rich volcanic rock also removes carbon dioxide from the atmosphere through a process called enhanced rock weathering.

Enhanced rock weathering (ERW) is a nature-based method of Carbon Dioxide Removal (CDR)  based on a geological process. In the planet’s carbon cycle, this process takes hundreds of thousands of years but

Silicate rock or basalt rock, when crushed into a fine powder, and spread on agricultural land then the rock begins weathering straight away, speed up by the increased reactive surface area. The basalt reacts with carbon dioxide to form stable carbonates, effectively storing carbon.

Hence, statement 1 is correct.

Ocean Alkalinity Enhancement

Ocean alkalinization is an approach to carbon removal that involves adding alkaline substances  with high pH to seawater to enhance the ocean’s natural carbon sink. These substances could include minerals, such as olivine, or artificial substances, such as lime or some industrial byproducts. Adding alkalinity to the ocean removes carbon dioxide (CO2) from the atmosphere through a series of reactions that convert dissolved CO2 into stable bicarbonate and carbonate molecules, which in turn causes the ocean to absorb more CO2 from the air to restore equilibrium. 

Hence, statement 2 is correct. 

Carbon capture and storage (CCS) 

Carbon dioxide emissions from industrial processes are captured and stored underground. Abandoned subterranean mines can serve as suitable storage sites, with the captured carbon dioxide pumped into these locations in the form of carbonated waters.

The process of capturing carbon dioxide (CO2) and storing it can be condensed into three stages: capture, transportation, and underground injection. Once discharged into rock formations, the CO2 is stored long-term.

Hence, statement 3 is correct.

Direct Air Capture 

Direct air capture encompasses land-based processes that directly remove carbon dioxide from the air via filtration. Carbon dioxide is then transported to storage reservoirs in solid or liquid form, where it is durably stored for hundreds to thousands of years. 

Microalgal cultivation

The large-scale farming of seaweed, also known as microalgal cultivation or aquaculture, draws down carbon dioxide from the atmosphere as part of the process of photosynthesis that occurs as the seaweed grows. 

Ocean Fertilization 

Ocean fertilisation is the addition of nutrients such as iron, nitrogen, and phosphorus to the surface of the ocean to stimulate the growth of phytoplankton that naturally absorb carbon dioxide during photosynthesis.

Coastal Blue Carbon 

The process by which coastal blue carbon ecosystems (e.g. seagrass, mangroves, and salt marshes) sequester and store carbon. Coastal blue carbon ecosystems absorb carbon from the atmosphere via photosynthesis.

Read: Previous Year UPSC Environment Questions (PYQs) With Explanation 2023