Carbon Capture Methods Compared: Forestation vs Direct Air Capture
Two camps for carbon capture have emerged – the natural camp and the technology camp. Here we match up forestation with Direct Air Capture (DAC) and look at the unique set of advantages and challenges of each.
(See here for more on the various carbon capture methods.)
Emissions Targets to Attain Net-Zero
Binding emissions reduction targets, both at a national and regional level, have increased the pressure on governments and industries to drive towards net-zero greenhouse gas emissions.
This has led to the rise in the voluntary carbon offset markets and carbon credit trading, which has opened up development across the various carbon capture methods and spurred the search for the most effective approaches.
The following looks at two carbon capture options.
Forestation (Afforestation/Reforestation)
Method
Afforestation/reforestation involves planting trees to absorb CO₂ from the atmosphere through photosynthesis and sequestering it in the trees and soil.
Land Area Requirements and CO₂ Capture Capability
Forestation requires considerable land area. The amount one hectare of forest can capture varies greatly from 4.5 to 40 tonnes of CO₂ per year (for the first 20 years), based on tree species, climate, location, age of the trees and forest density. [One Tree Planted]
For example, maturing commercial spruce forests can capture around 25 tonnes of CO₂ per hectare per year, while oak-mixed deciduous woodlands can capture approximately 18 tonnes of CO₂ per hectare per year. [Farm Advisory Service]
Dr Malcolm Fabiyi, Founder of OptimaBiome, explains:
“To get to net-zero via forestry carbon removals (alone) we will need 2 billion hectares to remove 40 billion tons of CO₂ per year. That is 13% of all the land mass on Earth.”
To put this into perspective, 95% of the World’s population lives on 10% of the land. [Science Daily]
Lifespan of Carbon Credit
Trees can sequester carbon for several decades to centuries, depending on species longevity and forest management practices.
However, destructive events like wildfires, deforestation or disease can release stored carbon. Having said that, forests themselves can last for many thousands of years as a whole and we need to preserve these in order for our planet to survive. We need to also look far into the future and set the Earth up to be a living, thriving habitat.
This raises the question about what the true value of a carbon credit is when the time value is taken into account. This should be viewed in the light of CO₂ being present in the atmosphere for a thousand years and a forestation credit being valid for about 100 years – which means, in essence, that you would have to buy 10 forestation credits to truly offset the carbon.
Forestation is part of the fast carbon cycle whereas the slow carbon cycle is CO₂ stored in the earth e.g. in fossil fuels. Human activity has disrupted the slow cycle by pulling out the fossil fuels and emitting the carbon into the atmosphere.
Scalability
Due to the vast tracks of land and long lengths of time required for effective forestation, scalability is a limiting factor. However, trees have been removing CO₂ for millions of years, that is to say, the ‘tech is working’ and needs no development as in the case of technological carbon capture methods.
Benefits of Forestation for Carbon Capture
- It is a natural, environmentally friendly process.
- Forestation provides co-benefits, including improved soil health, biodiversity, and local economic benefits.
- It has a low-cost compared to technological solutions at $30 – $50/tonne of CO₂ captured. [UN-REDD]
- Forestation enhances biodiversity and ecosystems.
- It has the potential for use in biochar CO₂ capturing.
- It has low energy requirements.
- Forestation does not need tech to be developed, and it is easy to implement.
- Forestation has no CO₂ storage or transportation issues.
Drawbacks of Forestation for Carbon Capture
- Forestation requires large areas of land.
- Carbon storage is temporary, as trees can decompose and release CO₂ or they can be destroyed in fires, droughts, floods, by disease or cut down.
- Forestation can run up against land availability, water and fertilizer requirements, and potential impacts on food security and biodiversity.
- Forests require continuous management.
- The carbon sequestration rate of the forest decreases as trees mature.
- It is not easy to get a precise verification and measurement of the amount of CO₂ captured for carbon credits/offsets purchases.
Direct Air Capture (DAC)
Method
DAC is technology that captures CO₂ directly from the ambient air using chemical processes. (See: How Does Direct Air Capture Work?)
Land Area Requirements and CO₂ Capture Capability
Direct Air Capture installations have a more compact physical footprint than forestation, especially when optimised using modular systems. For context, to capture one billion tonnes of CO2 using DAC would take 0.012 million hectares (area of Dublin City) whereas using forestation it would require 200 million hectares (area of Mexico).
Different DAC systems capture different amounts of carbon dioxide, but a basic unit would capture around 1,000 tonnes of CO₂ per hectare per year, making DAC substantially more efficient in terms of land use compared to forestation.
Using NEG8 Carbon as an example:
The area of a DAC park comprising of 12 x 6000 tonnes per annum NEG8 DAC towers is 5 hectares, capturing 72,000 tonnes per year. This equates to 14,400 tonnes CO₂ per hectare per year.
Lifespan of Carbon Credit
If the captured CO₂ is stored underground, it will be trapped for thousands of years, and furthermore, if it is mineralized it will be permanently sequestered. Alternatively, it can be used in durable products such as in concrete production. (For more details see: What is Carbon Sequestration? and What is CO₂ Utilization?)
Scalability
As DAC technology advances, the costs are coming down and the efficiency is improving, which makes it more simple to scale. We are already seeing the fruits of investments and commitments to achieving this end.
Benefits of DAC
- DAC can remove CO₂ directly from the atmosphere at any location, regardless of the source.
- It requires a smaller footprint compared to afforestation/reforestation.
- Direct Air Capture removes CO₂ emitted from hard-to-abate industries that point source cannot cover, such as aviation and agriculture. (See: Direct Air Capture vs Point Source)
- DAC offers precise measurement and verification for purchasing carbon credits offsets.
- Direct Air Capture can use off-grid renewable energy that does not interfere with the local electricity grid.
For more see: The Advantages of Direct Air Capture
Drawbacks of DAC
- DAC can be energy-intensive which affects costs, however, ongoing development is bringing these figures down.
- Compared to forestation, it requires more infrastructure for capturing and storing CO₂.
- Currently, storage options for the captured CO₂ are under-developed.
To sum up, we have put the core points into a table.
Comparison Table
| Forestation | Direct Air Capture (DAC) | |
| Method | Planting trees to absorb CO₂ via photosynthesis and sequestering in trees and soil | Capturing CO₂ from ambient air using chemical processes |
| Land Area Requirements | Requires significant land area | More compact, especially with modular systems |
| CO₂ Capture per Unit | Varies by species, climate, and density; around 4.5-40 tonnes CO₂ per hectare per year | 1,000 tonnes CO₂ per hectare per year and more depending on the technology |
| Lifespan of Carbon Credit | Decades to centuries, but susceptible to disturbance (e.g. fire and disease) | Long-term (1000’s of years) when stored underground; permanent if mineralized |
| Scalability | Limited by land availability and time; no tech development needed | Growing potential as technology improves |
Example of Forestation vs Direct Air Capture
Here we look at a rundown of using NEG8 Carbon’s Direct Air Capture technology to capture 8 million tonnes of CO₂ per year (the amount emitted by Ireland’s hard-to-abate industries) compared to using forestation to capture the same amount.
NEG8 Carbon’s Director of Technology, Prof. Don MacElroy, explains:
The area of one DAC park built using NEG8’s DAC towers is 5 hectares capturing 72,000 tonnes per year. To capture 8 million tonnes per year we would need 111 DAC parks covering an area of 2.4 km2 or 240 hectares (half the area of Dublin Airport).
Forestation requires about 100,000 hectares per million tonnes of CO₂ captured per year. Therefore, for 8 million tonnes per year we would need 800,000 hectares.
Note: The Afforestation Scheme proposed by the Irish Government aims to plant 8000 hectares of trees per year, subject to funding and land, to reach 18% forest cover, up from the 11% today. This means ultimately planting a total of 600,000 hectares which will take 75 years. Therefore, to capture 8 million tonnes of CO₂ through this program we would need 100 years.
Conclusion
All the carbon capture players are fighting towards a common goal: net-zero and beyond to carbon negativity to fight climate change.
Forestation is a natural, cost-effective option but can be unpredictable. On the other hand, DAC offers reliable, efficient and compact carbon removal but at a higher cost. Using all methods available where they make the most sense may be the most practical path to achieving global carbon reduction goals.
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