UPSC Prelims 2023 Q68: Carbon Capture & Sequestration Methods

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?

  1. Only one
  2. Only two
  3. All three
  4. None

Answer: (c) All three

Statement-wise explanation

  • 1: correct — This is 'enhanced rock weathering'. Basalt is rich in calcium- and magnesium-bearing silicate minerals. Grinding it finely gives it a much larger surface area, so it reacts faster with CO2 dissolved in rain and soil water. The CO2 becomes bicarbonate, which drains to the oceans and stays locked away for very long periods. The IPCC's Sixth Assessment Report (2022) lists enhanced weathering among its carbon dioxide removal options.
  • 2: correct — This is 'ocean alkalinity enhancement', also called 'ocean liming'. Adding lime (calcium oxide or hydroxide) makes seawater more alkaline. The water then turns more of its dissolved CO2 into bicarbonate and carbonate ions, so the ocean can take up more CO2 from the air. The IPCC also lists ocean alkalinity enhancement as a carbon dioxide removal method, and it would counter ocean acidification as well.
  • 3: correct — This is geological storage of captured CO2, the 'storage' step in CCS/CCUS. Proposed sites include deep saline aquifers, depleted oil and gas fields, unmineable coal seams and abandoned mines. Injecting the CO2 dissolved in water ('carbonated water') is a tested method. Iceland's CarbFix project pumps CO2 dissolved in water into basalt, where it turns into carbonate minerals.

How to eliminate

Option-structure logic helps only a little here. All three activities rest on the same chemistry: CO2 reacts with calcium or magnesium and ends up as stable bicarbonate or carbonate. Statement 3 is plainly the textbook definition of capture-and-store, so it is certainly correct. That rules out 'None'. Statements 1 and 2 sound unusual, but the question says 'often considered and discussed', not 'proven' or 'deployed at scale'. That wording is generous and points toward including the speculative geoengineering ideas too. To answer with confidence you need one fact: enhanced weathering of basalt and ocean alkalinity enhancement (liming) are both standard carbon dioxide removal methods in the IPCC's list. Remember that list: afforestation, soil carbon, biochar, BECCS, DACCS, enhanced weathering, ocean alkalinity enhancement, ocean fertilisation, blue carbon.

Know more

Carbon capture and sequestration (CCS) covers two related ideas:

  • Point-source CCS/CCUS: catching CO2 at a chimney (power plant, cement, steel, refinery). The CO2 is then used (urea, methanol, enhanced oil recovery) or stored underground.
  • Carbon dioxide removal (CDR): pulling CO2 that is already in the air back out. The IPCC says CDR is unavoidable for net zero, because some sectors cannot cut emissions fully.
Method How it locks carbon Type
Geological storage CO2 injected into saline aquifers, depleted oil/gas fields, unmineable coal seams, old mines CCS
Mineral carbonation (e.g. CarbFix, Iceland) CO2 dissolved in water reacts with basalt and forms solid carbonates CCS
Enhanced rock weathering Crushed basalt/olivine on fields reacts with CO2 and forms bicarbonate CDR
Ocean alkalinity enhancement Lime or minerals raise seawater pH, so the ocean absorbs more CO2 CDR
Ocean fertilisation Iron added to boost plankton, which take up CO2 CDR (contested)
BECCS / DACCS Biomass energy + CCS; machines that scrub CO2 from air CDR
Biochar, afforestation, soil carbon, blue carbon Carbon stored in biomass and soils CDR (biological)

Why basalt matters: basalt is a dark igneous rock, rich in calcium, magnesium and iron silicates. These react readily with CO2. India's Deccan Traps are a vast basalt province, so researchers see them as a possible CO2 storage site.

India's policy track:

  • NITI Aayog report, CCUS Policy Framework and its Deployment Mechanism in India (November 2022).
  • Net zero target: 2070.
  • Union Budget 2026–27: ₹20,000 crore CCUS programme for power, steel, cement, refineries and chemicals.

Trade-offs examiners like: weathering and liming need huge amounts of mined rock, energy for grinding, and transport. Their effects on ecosystems are uncertain, and measuring how much CO2 they actually remove (MRV) is hard.

In the news

In November 2022 NITI Aayog released its report on a CCUS policy framework for India, and the IPCC's 2022 mitigation report put new focus on carbon dioxide removal methods such as enhanced weathering and ocean alkalinity enhancement. Both kept carbon capture in the news in the months before the 2023 Prelims.

NCERT Concepts to Revise

  • Basalt: Statement 1 depends on why basalt, a calcium- and magnesium-rich igneous rock, can react chemically with carbon dioxide.
  • Global warming: All three activities are judged on whether they take CO2 out of the air to slow long-term warming.

Read more