Storing carbon: essential to achieve the Net Zero objective?

2024-04-11 09:30:42

As the climate emergency becomes more and more pressing, carbon reduction and storage are becoming essential. To achieve this, different options based on environmental preservation or cutting-edge technologies are being studied.

Over the past few centuries, human activities have released more than 2 trillion tons of carbon dioxide into the Earth’s atmosphere. To limit global warming, we must reduce our CO emissions₂. In France, the National Low Carbon Strategy (SNBC) aims to limit the increase in temperatures to +1.5°C compared to the pre-industrial period and to achieve a balance between CO emissions and absorptions.₂ by 2050. This threshold is called carbon neutrality or “net zero emissions”. To achieve this, two solutions must be put in place: the direct reduction of carbon dioxide emissions and the increase in carbon sinks.

According to the IFPEN website, “ the International Energy Agency estimates, in the Net Zero Emission by 2050 (NZE) scenario made public in 2021, that to achieve carbon neutrality in 2050, 7.6 Gt of CO₂ must be captured per year from 2050, i.e. 20% of current emissions ».

Different carbon capture techniques

Different CO capture, storage and valorization techniques₂ (CCUS-Carbon Capture, Use and Storage) are developing. Some are based on the natural accumulation of CO₂ by preserving the environment. We can thus mention:

• tree planting and forest expansion;
• safeguarding the coastal coastline which includes salt marshes and seagrass meadows, real carbon sinks. By preserving them and restaurants, it is possible to prevent erosion and protect species;
• the reconstitution of marine ecosystems which would encourage the movement of carbon from the surface to the depths thanks to currents and food chains. Carbon is contained in plants and animals that fall to the ocean floor when they die.

Other solutions are being studied to promote the absorption of carbon from natural environments:

• adding nutrients such as iron, phosphorus and nitrogen to waters to increase the ability of phytoplankton to absorb carbon dioxide through photosynthesis;
• grow carbon-rich algae. Their roots buried in the seabed store carbon or transform it into nutrients;
• adding non-acidic alkaline substances to the ocean to extract and fix carbon in rocks and sediments;
• bringing deep, cold, nutrient-rich waters to the surface to increase phytoplankton production;
• limit plowing of agricultural soils and plant cover crops to reduce carbon release from agricultural land.

Finally, other solutions propose using the latest technological innovations to capture CO₂ :

• using giant fans to capture CO₂ and trap it using solvents. The carbon is then reused or stored underground. Due to the low concentration of CO₂ in the air, it is a very expensive solution;
• exploit biomass to produce energy. The CO₂ released during this combustion is reused or stored;
• use basalt, which naturally binds to atmospheric carbon to sequester it in underground rock slabs;
• passing an electric current through seawater to directly remove carbon dioxide;
• capture and reuse or store carbon dioxide from factory fumes by washing the vapors with solvents.

Once captured, carbon can be stored in two different structures: deep saline aquifers which are reservoirs of non-potable salt water located on the ocean floor, or depleted hydrocarbon (oil and gas) deposits. According to IFPEN “global CO storage capacity₂ would be between 8,000 and 55,000 gigatons. Thus, even the lowest figure (8,000 Gt) far exceeds 100 Gt of CO₂ which should be stored by 2055 in the “sustainable development” scenario ».

A controversial solution

Carbon capture remains a controversial topic. While no one questions the merits of ecosystem preservation solutions, some environmental defenders question the legitimacy of CCUS technologies. Indeed, in 2016, thirteen major oil companies created a billion-dollar fund, the Oil & Gas Climate Initiative, to develop these solutions. Environmental advocates fear these technologies will be a distraction from those who have contributed to the climate emergency and prevent emissions from being reduced. They fear that polluters will profit from the pollution they generate.

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