In December 2015, 195 countries plus the European Union reached a consensus to tackle climate change and, as a result, the Paris Agreement was signed in April 2016. This international treaty was focused on climate change mitigation with the goal to limit temperature increases to 1.5°C (2.7°F). Looking back now, 8 years later, this still seems like an ambitious plan and the Intergovernmental Panel on Climate Change (IPCC) is stressing that reducing emissions is not enough, active removal of CO2 from the atmosphere is essential for reaching these goals.
Unless you have been living under a rock, you would have heard about the link that was made between carbon dioxide and the greenhouse effect. CO₂ (and other greenhouse gases) absorbs IR (thermic) energy – this energy is then dispersed in all directions - some of which gets re-emitted into the Earth’s atmosphere and some of it back into space. In less than 200 years, human activity (population growth, industrialisation, agriculture etc.) has raised the content of carbon dioxide in the atmosphere by 50%!
This is where CCS (Carbon Capture and Storage) comes into play as a way of reducing CO₂ emissions into the atmosphere, an essential step into reducing global warming. CCS is a three stage process that aims to capture the carbon dioxide produced by industrial sites before it is released into the atmosphere (such industrial sites include power generation plants, hydrogen production and cement or steel factories). The three staged process consists of :
CO₂ capture at the emission source
Transportation (using pipelines, ships etc.)
Storage – by injecting it deep underground, usually in depleted gas/oil reservoirs as well as saline aquifers – geological formations made of permeable rocks saturated with salt water.
Sometimes the captured CO₂ is used in other industrial processes. It is also possible to remove CO₂ from air in cases where emissions are difficult to avoid. Direct air capture (DAC) pulls the carbon dioxide directly from the environment – air.
Carbon Capture and Storage started as early as 1972 in Texas, USA, where more than 200 tons of CO₂ emissions from natural gas plants have been captured and stored underground. Currently there are more than 45 commercial carbon capture sites globally, with an overall capacity surpassing 50 Mt of captured CO₂. However, this would make up for only 40% of the net zero ambitions for 2030.
We all hope that technical advancements will speed up this process while also making it cheaper, still, a research paper published earlier this year in Science Daily (ETH Zurich) is predicting that the costs of CCS will remain high, with an estimate for 2050 of 230-540 USD per tone of captured CO₂ – this is double the price of the previous estimates.
While best efforts are being made to tackle the carbon emissions in the most technologically efficient ways, there are voices that are stressing the importance of the natural methods of reducing CO₂ from the atmosphere – by preserving mature forests. In an interview with Yale Environment 360, policy scientist William Moomaw explained that mature forests have a greater capacity to store CO₂ compared to newly planted ones and that is essential to preserve and protect forests ranging between 70-125 years old as they have the greatest potential to remove carbon from the atmosphere. From the 11 billion tons of carbon we are releasing every year in the atmosphere, the vegetation on Earth is storing 6.3 billion tons.
According to a Swiss study, The global tree restoration potential, the restoration of forests worldwide remains one of the most effective tools in mitigating climate change. An extra 0.9 billion hectares of forest would store about 25% of the carbon currently in the atmosphere.
0.9 billion hectares is a lot – it would mean increasing the total area covered by forests by 25%, but just as a side note, in the last 50 years the Amazon rainforest has lost 17% of its area.
There has been an increasing interest in the carbon storage potential of large trees and we should maintain this momentum. A recent study published in the Royal Society is analysing the giant sequoias and their growth rate and concluded that such trees make a good choice from a carbon storage perspective.
I found a visit at the Natural History Museum in London particularly inspiring – their giant sequoia slice offers an impressive reminder: when this old sequoia tree was cut down in 1893, the global forest area was approximately 5.5 billion ha. After a century, this area shrunk to 4.24 billion ha, with less than 4.1 billion ha remaining today. It is estimated that 15 billion trees are being felled annually and this stark reality highlights the urgent need to safeguard our planet's forests, which serve as essential natural carbon capture systems, alongside the development of technological solutions.
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