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ecology

Reaching for CO2

Carbon moves through a continuous cycle within the Earth’s system—passing through the atmosphere, oceans, plants, and rocks. However, human activities, particularly the extraction and burning of fossil fuels, disrupt this cycle. This disturbance aggravates the natural balance, increasing atmospheric carbon levels through greenhouse gases such as carbon dioxide and methane. The excessive accumulation of these gases leads to global warming. While some carbon eventually re-enters the cycle, much remains trapped in the atmosphere, failing to return to its original state.

Warnings like “If we don’t take action now (or rather, should have acted yesterday?), climate phenomena such as wildfires, extreme urban heat, and rising sea levels will only worsen” are frequently repeated. Yet, their constant repetition has led many of us—ordinary inhabitants of the planet—to become insensitive, reacting with indifference rather than urgency.

Those who grasp the long-term severity of the issue—scientists, governments, health organisations, and other concerned stakeholders—are actively preaching the problem. They work to develop technologies and strategies that mitigate climate change, focusing on cost-effective and efficient methods to extract carbon from the atmosphere and reintegrate it into the natural cycle. Some of the techniques developed so far include:

Forest and soil recovery ⋙

One of the oldest and most reliable methods is reforestation and forest conservation, as trees absorb carbon from the air. Another approach involves enhancing soil carbon sequestration on farms by planting cover crops, enriching the soil with compost or fertilisers, and reducing tillage. According to the World Resources Institute, the potential carbon sequestration of forests and urban tree plantations in the U.S. alone exceeds half a gigaton per year—comparable to the country’s annual agricultural emissions. A significant advantage of this method is its relatively low cost compared to other carbon removal techniques. Additionally, forests serve as invaluable reservoirs of water and natural air filters, providing multiple environmental benefits beyond carbon capture.

Bioenergetics ⋙

The Biofuels and Carbon Sequestration method involves using plants both as biofuels and for carbon sequestration. Crops like corn and switchgrass absorb carbon from the atmosphere as they grow and store chemical solar energy in their biomass. This biomass can be burned directly or converted into renewable liquid or gaseous fuels. In a process known as bioenergy with carbon capture and storage (BECCS), these plants are combusted at generating stations to generate electricity. Meanwhile, carbon byproducts are collected and stored beneath the surface. This approach enables energy production for industries, electricity, and transportation while preventing carbon from re-entering the atmosphere by storing it underground or incorporating it into durable materials like cement.

However, BECCS has significant drawbacks. It often requires cultivating specific crops that compete with food production, potentially harming natural ecosystems and worsening food security. Some carbon sequestration methods remain poorly understood and may cause unintended environmental consequences. For example, ocean fertilisation—adding iron and other nutrients to seawater to stimulate phytoplankton growth—enhances carbon absorption but risks disrupting marine ecosystems and harming sea life.

More promising BECCS approaches involve using waste—such as household or agricultural byproducts—rather than dedicated crops. This method has a significant advantage: it does not require additional land, one of the most valuable and limited resources.

Direct Air Capture and Carbon Sequestration ⋙

CO2 can be extracted directly from the air using large-scale air filtration systems and stored underground afterwards. This technology already exists and has been implemented on a small scale. However, the process faces significant challenges, primarily due to its slow rate and high cost.
Direct air capture remains financially and energy-intensive, requiring substantial amounts of heat and electricity. In fact, removing just one gigaton of carbon from the atmosphere would consume approximately 10% of the world’s total energy supply. While this method is a key aspect of geoengineering, it is not the only one. Other approaches, such as solar radiation management—which aims to reduce the amount of sunlight reaching the Earth—could also help mitigate climate change. Yet, they do not address the root cause of rising greenhouse gas levels.
Investment in carbon capture technology and improvements in clean and affordable renewable energy could enable large-scale adoption of this method.

Carbon Mineralisation ⋙

Certain minerals can react with carbon chemically, converting it from a gas into a solid state through a process known as carbon mineralisation or mineral weathering. In nature, this process occurs extremely slowly, taking hundreds or even thousands of years. To accelerate it, scientists are developing various technologies, including:

  • Pumping alkaline fluids from underground vents to the surface allowing them to react with atmospheric carbon.
  • Blowing air through mine tailings—rocks discarded from mining operations that contain minerals capable of capturing carbon.
  • Crushing minerals or using specialised enzymes to increase their surface area, enhancing their ability to absorb carbon.
  • Weathering industrial byproducts, such as fly ash, furnace dust, or iron and steel slag, promote carbon absorption.

This technology is primarily being developed by startups focused on creating new building materials that utilise carbon mineralisation.

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