What is Carbon Sequestration ? (Part – 1)

Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide (CO₂) to reduce its concentration in the atmosphere. This can occur naturally or be facilitated through human intervention. The primary goal of carbon sequestration is to mitigate climate change by decreasing the amount of greenhouse gases contributing to global warming.

Why Carbon Sequestration

Before the Industrial Revolution, Earth’s atmosphere was a delicate balance of gases, including less than 300 parts per million (ppm) of carbon dioxide (CO₂). This balance maintained a global average surface temperature of around 15°C, which was perfect for ecosystems and human civilizations to flourish.

But then came the Industrial Revolution. With coal-fired factories, steam engines, and later, oil-powered industries, humans began burning fossil fuels at an unprecedented rate. This released massive amounts of stored carbon into the atmosphere as CO₂, pushing the levels steadily upward. Fast forward to today, and atmospheric CO₂ concentrations have reached 422.4 ppm—a level not seen in millions of years. The rate of increase is alarming, with 2-3 ppm being added every year due to ongoing emissions.

The result? A greenhouse effect that traps more heat in Earth’s atmosphere. This year, July 2024 marked a grim milestone as the global average temperature breached 17°C, making it the hottest day ever recorded. Out of the top 10 warmest years on record, all 10 occurred in this millennium, illustrating the accelerating pace of global warming.

The Challenge: How Do We Fix This?

To address the crisis, the solution has two parts:

1. Reduce new emissions by transitioning to clean energy, improving efficiency, and altering consumption habits.
2. Handle the emissions already released—the CO₂ that’s sitting in the atmosphere, contributing to climate change.

This is where carbon sequestration enters the story: moving CO₂ out of the atmosphere and storing it safely elsewhere.

Carbon Sequestration: The Science of Moving CO₂

Imagine we could store CO₂ in balloons and tuck them away in our attics (laughable, right?). While impractical, the real-world alternatives are surprisingly effective:

Long-Term Storage: Geological Sequestration

• CO₂ can be injected deep beneath the Earth’s surface, into rock formations or depleted oil fields, where it stays trapped for millennia.
• The oceans, Earth’s largest carbon sink, naturally absorb CO₂, though this process needs careful management to avoid harming marine life.

Short-Term Storage: Biological Sequestration

Planting trees: Plants absorb CO₂ as they grow.

• Imagine a mature tree weighing 1000kg tree saturated with water. Half of its weight, or 500kg, is water. The remaining 500kg is dry mass, and 47.5% of that, or 237.5kg, is carbon.
• To understand how much CO₂ this tree absorbed, we need to consider the ratio of CO₂ to carbon. Carbon has a molar mass of 12, while oxygen has a molar mass of 16. In CO₂, one carbon atom combines with two oxygen atoms, giving it a molar mass of 44. So, to produce 1kg of carbon, we need 44/12 = 3.67kg of CO₂.
• Therefore, our 237.5kg of carbon required 237.5 × 3.67 = 871.63kg of CO₂.
• To calculate the annual CO₂ absorption, we need to estimate the tree’s age. A ton-sized tree is likely between 30 and 40 years old. Assuming 35 years, this tree absorbed approximately 25kg of CO₂ per year. (Source )

However, this storage is temporary. When trees die, decay, or are burned, the CO₂ returns to the atmosphere.

How it Work ?

Mechanisms and Processes of Carbon Sequestration

1. Carbon Fixation by Plants

Plants play a crucial role in the natural carbon cycle through photosynthesis, where they absorb carbon dioxide (CO₂) from the atmosphere and convert it into organic compounds like glucose. This process stores carbon in plant biomass (leaves, stems, and roots) and in the soil when plant matter decays.

• Storage Potential: Forests, grasslands, and agricultural crops are significant carbon reservoirs.
• Limitations: This is a temporary solution, as carbon can return to the atmosphere when plants die, decay, or are burned.

2. Microbial Decomposition and Soil Carbon Dynamics

Soils store a significant portion of Earth’s carbon, largely influenced by microbial activity:

• Decomposition Process: Microbes break down organic matter (e.g., dead plants and animals), releasing CO₂ back into the atmosphere or transforming it into stable soil organic carbon (SOC).
• Factors Influencing Storage: Soil type, moisture, temperature, and land-use practices affect how much carbon remains stored.
• Soil as a Carbon Sink: Practices like no-till farming, cover cropping, and organic amendments can increase SOC, enhancing carbon sequestration.

3. Geological Trapping Mechanisms

Geological carbon sequestration involves capturing CO₂ and storing it deep underground. This is a more permanent solution, relying on Earth’s natural structures to lock CO₂ away for millennia. Key mechanisms include:

1. Structural Trapping:
   • CO₂ is injected into porous rock layers beneath impermeable caprocks, which act as a seal to prevent gas from escaping.
   • Examples: Depleted oil and gas reservoirs.
2. Mineral Trapping:
   • Over time, CO₂ reacts with minerals in the rock to form stable carbonate minerals, effectively “locking” the carbon in solid form.
   • Example: Basalt formations.
3. Residual Trapping:
   • As CO₂ is injected into porous rock, small amounts become trapped in tiny pores due to capillary forces.
   • This mechanism provides stability even if other trapping methods fail.