Restoring soil carbon can reverse global warming, desertification and biodiversity loss
February 21, 2008
Land use change — including deforestation, bush fires, and soil degradation — accounts for roughly 20 percent of global greenhouse gas emissions, but land management practices can be used to reduce emissions. While reforestation and avoided deforestation have garnered a lot of attention of late, restoration of other forms of vegetation can dramatically increase the capacity of degraded landscapes to store carbon.
Tony Lovell of Soil Carbon P/L in Australia estimates that by actively supporting regrowth of vegetation in damaged ecosystems, billions of tons of carbon dioxide can be sequestered from the atmosphere.
In February 2008, Lovell discussed the potential of soil carbon restoration.
Mongabay: What are the advantages of increasing the capacity of soil to store carbon?
In arid and seasonally dry areas, continuous grazing creates disasters like that on the left. Returning to herding-style management with long recovery periods between grazings heals the land (right)
Determining how much carbon dioxide (CO2) can physically be consumed from the atmosphere?
LEFT: This river in Zimbabwe used to flow year-round. Then overgrazing by wandering livestock bared much of the soil in the surrounding area. Today the river flows only as flash floods following heavy rains. Biodiversity loss is severe, livestock are starving, and most wildlife has disappeared. RIGHT: This nearby river had similar problems. It now has water year-round, and flows during most of the year. Drought is rare, biodiversity is increasing, and wildlife has reappeared in large numbers. Soil Carbon P/L notes that capturing just 1 mm more rain per year means: 1 liter more usable water per square meter; 10,000 liters more water per hectare; 1,000,000 liters more water per square kilometer; Less drought, because more water stays in the soil to recharge rivers, springs, and wells; and more forage, because plants can also use that water.
Consumption of CO2 per hectare
- One hectare is 10,000 sq. metres. If a hectare of soil 33.5 cm deep, with a bulk density of 1.4 tonnes per cubic metre is considered, there is a soil mass per hectare of about 4,700 tonnes.
- If appropriate management practices were adopted and these practices achieved and sustained a 1% increase in soil organic matter (SOM)6, then 47 tonnes of SOM per hectare will be added to organic matter stocks held below the soil surface
- This 47 tonnes of SOM will contain approximately 27 tonnes of Soil Carbon (ie 47 tonnes at 58% Carbon) per hectare
- In the absence of other inputs this Carbon may only be derived from the atmosphere via the natural function known as the photo-synthetic process. To place approximately 27 tonnes of Soil Carbon per hectare into the soil, approximately 100 tonnes of carbon dioxide must be consumed out of the atmosphere by photosynthesis
- A 1% change in soil organic matter across 5 billion hectares will sequester 500 billion tonnes of physical CO2
- Every 1% increase in retained SOM within the topmost 33.5 cm of the soil must capture and hold approximately 100 tonnes per hectare of atmospheric carbon dioxide (the variability in the equation being due only to the soil bulk density). We submit that under determined, appropriate management, that this is readily achievable within a very few years
- For each 1% increase in SOM achieved on the 5 billion hectares there will be removed 64 ppm of carbon dioxide from atmospheric circulation (500,000,000,000 tonnes CO2 / 7,800,000,000 tonnes per ppm = 64 ppm).
- Soil Organic Matter is the plant material released into the soil during the natural phases of plant growth. It includes root material sloughed off below the soil surface and plant litter carried into the soil by microbes, insects and rainfall
- Soil Carbon is the elemental carbon contained within Soil Organic Matter (SOM).
- One tonne of CO2 contains 12/44 units of carbon (ie 0.27 tonnes of carbon per tonne of CO2.). Therefore 27 tonnes of carbon sequesters 27/0.27 = 100 tonnes CO2 (rounded). NB Carbon atomic weight 12, oxygen atomic weight 16 ie CO2 = 12+(16+16) = 44
TOP: This cattle ranch in Sonora, Mexico, is typical of hundreds of millions of hectares of grazing land in arid and seasonally dry areas worldwide. BOTTOM: This is the neighboring ranch, La Inmaculada. The ranch is in the same area; has the same rainfall, same soils, and same plant species. The pictures were taken on the same day and La Inmaculada actually has more cattle than the drier ranch. The only difference between the two is management
Mongabay: How does one restore carbon to the Earth?
Lovell: By actively mimicking nature and thereby allowing natural cycles to reinvigorate. Arid and semi-arid grazing lands co-evolved with massive herds of grazing animals that were kept bunched up by the presence of pack-hunting predators. When humans removed these predators and fenced in the animals we severely disrupted this natural behaviour leading directly to desertification and massive release of soil carbon into atmospheric circulation. The process that actually removes CO2 from atmospheric circulation is photosynthesis. A simple question for anyone — think of the biggest plant you have ever seen — it is probably a huge tree more than 50 metres tall, 10 metres around and weighing hundreds of tonnes. You can walk up to this tree and hit it — it is solid. Where did the material come from to make this tree? Far too many people answer — "from the ground the tree is growing in". The truth is that over 50% of the solid "thumpable" bit of the tree came directly out of the atmosphere as CO2. While a tree is much more visible than grass, the result is the same.
The global opportunity and numbers
Mongabay: What does Soil Carbon Australia offer?
Lovell: Our main focus is on raising awareness of the important role soil carbon plays in mitigating global warming, and ideally on having it recognized as a tradeable item under any global emissions trading scheme. This will dramatically change the incentives that farmers respond to and thus bring about a massive positive change in agricultural practices.
Mongabay: Where are you working?
Lovell: We are based in Australia, and have colleagues in the USA, New Zealand, Spain, England, South Africa and South America.
Mongabay: Have you looked at the potential to earn carbon credits for sequestration?
Lovell: Yes — it is widely recognized and accepted that soil carbon sequestration works — the only questions are ones of measurement, monitoring and verification (MMV). We as a society have dealt eith these MMV issues in regards to afforestation and deforestation so should be able to do so with regards to soil carbon.
Mongabay: Are you familiar with "terra preta" soils in the Amazon? If so, how does your process compare with this form of soil carbon?
Lovell: "terra preta" is probably the best example of just what we are talking about — a carbon rich, biologically active soil created as a result of appropriate human management. In the 5 billion hectares we want to bring attention to the results will not be as dramatic due to the lower rainfall and inherently poorer quality of the soils themselves, but the results will be significant and well worthwhile.
*This was erroneously listed as 455 ppm