I’ve struggled with how to present biochar for it is only one answer to a more complex issue. The science behind what we all could be doing to combat climate change includes many environmental issues such as how we grow our food, how we deplete soil and water resources, how the carbon cycle has become corrupted, how we dump rather than recycle our waste, how we use energy and perhaps most importantly how population levels come to impact everything we might try.
Rather than trying to include all aspects of biochar I thought I would pass along a few pages of naturalist and environmentalist Tim Flannery’s book Here on Earth A Natural History of the Planet. His description of biochar as a tool in fighting climate change is a concise look at what biochar is and why replenishing earth's soil carbon store is so important. The tough part though is that it requires turning around an intransient cultural paradigm.
I will follow the comments to see what kind of follow on diary might help point the reader to a deeper understanding of how to make, or acquire or use biochar.
If truth be told, we citizens of the developed world have been promising for years at environment meetings to pay to protect the world's tropical forests. First at the Rio Earth Summit in 1992, then at Kyoto, and again in Copenhagen, the poorest countries are bitterly cynical that progress can be made. Natural justice tells us that it must be done, and we can only hope that the $100 billion promised by developed countries at Copenhagen will allow the poorest of our brethren to improve their lives in ways that protect the forests, and at the same time help obtain global climate security.
Tropical forests are not the only means of storing CO2. Opportunities also exist in agriculture, forestry, rangelands management and even national parks. One technology, called pyrolysis, transforms biological carbon (the kind that's present in plants and animals) into a mineralized form [biochar]. When plants and animals die they rot, releasing their carbon stores into the atmosphere. Mineralized carbon won't rot, so if it's added to soil it will stay there for hundreds or thousands of years. Pyrolysis works like a coal-fired power plant in reverse. Rather than feeding coal we've mined into a furnace and releasing its CO2 to the atmosphere, pyrolysis uses the carbon captured by plants and turns it into a mineral form, which can be buried in the ground.
Crop waste, animal manure, forestry off-cuts, even human sewage can be used as a feedstock for pyrolysis, and the process requires no external energy source except at start-up. The feedstock is heated in the absence of oxygen, separating it into solid, liquid and gas fractions. The solid is mostly biochar (mineralized carbon), the liquid is a bio-oil, and the gas is made of carbon monoxide, methane and other compounds. Both the bio-oil and gas, which are rich in hydrogen, can be burned for energy. This releases some carbon into the atmosphere, but overall more carbon is removed from the atmosphere than is added. Alternatively, the bio-oil can substitute for crude oil in the manufacture of many products, from transport fuels to fertilizers and plastics.
Up to 35 per cent of the carbon present in the feedstock can be transformed into biochar. If ploughed into soil, most of the carbon in the biochar will remain there for hundreds or thousands of years. Biochar generated by pyrolysis is unique in that it is a long-term, safe and proven means of sequestering carbon. Most experts consider that a billion tones of carbon per year could be stored as biochar in soils.
And there are other benefits. When dug into soil, biochar decreases soil acidity and delivers residual nutrients and minerals. Bacteria and soil fungi essential to healthy plant growth soon colonise its porous structure. Its filtering capacity purifies water and assists moisture retention, enhancing plants' access to nutrients and moisture, thus providing a longer growing period. There are also indications that emissions of nitrous oxide, a powerful greenhouse gas generated by soil bacteria, are significantly reduced when soils are treated with biochar.
Numerous experiments indicate that yields across a variety of crops, from carrots to grains and fodder, generally increase when biochar is added to soils. The impact is often greatest in leached tropical soils that lack carbon, with increases in yield of between 50 and 300 per cent recorded. In better quality soils yield increases, typically of around 7 to 20 per cent, have been documented. Estimates of how much biochar might boost global food yields are yet to be calculated. But anything that can help water quality and conservation, increase food production, produce clean energy and help fight climate change is a welcome addition to our basket of technologies.
The sequestration of carbon in tropical forests, or in the form of biochar, is limited. Forests grow slowly-the optimal uptake of carbon by a newly planted seedling is decades away-and pyrolysis machines take time to build and get operating. This means that neither will be contributing optimally to combating climate change for a couple of decades. There are, however, other options that allow us to store carbon quickly and on a large scale. Principally, they involve modifications to the way we manage our agricultural soils and the world's rangelands (lands used for grazing), and the way we manage fire in the dry tropics, all of which can be broadly categorized as better management of our soils.
Soils represent a huge carbon reserve-around 150 billion tones worldwide, which is roughly twice the amount of carbon in the atmosphere. It's three times as much as is contained in vegetation. Soil carbon has three principal components: humus, charcoal (from forest/grass fires) and the roots and other underground parts of plants. Humus is relatively stable, a carbon-rich organic material composed of strong, long chains of carbon molecules. It's what makes soil look black. It has a large capacity to hold mineral particles, which are valuable to plants, and can absorb most of its weight in moisture. While it's an important element of soil carbon, humus is not the most prevalent form of carbon in our soils. That honor goes to living plant tissue, mainly in the form of plant roots.
The world's intensively used croplands have lost 30 to 75 per cent of their carbon content over the past two centuries; that is around seventy-eight billion tones of carbon. When combined with the carbon lost from poorly managed rangelands and from eroded soils (neither of which has been reliably estimated), it's clear that a huge amount of carbon has moved from soils into the atmosphere. While this is bad news, there is a silver lining: with appropriate management it's possible to restore around two-thirds of the carbon lost from cropland soils within twenty-five to fifty years. And for every ton of soil carbon restored, 3.667 tones of CO2 is drawn from the atmosphere! (The apparent discrepancy is because the oxygen in the CO2 molecule is stripped off during photosynthesis.) So, through restoring our intensively used agricultural soils, we could draw down around 140 billion tones of atmospheric CO2.
Much soil carbon has been lost through traditional ploughing, which really is a declaration of war on biodiversity-the farmer rips out all life before planting a monoculture, which is kept 'pure' with pesticides and herbicides. Modern ploughing practices such as 'zero till' and 'zero kill' involve the planting of a crop directly into pasture grasses. Such practices are creating a new agricultural revolution, one based upon coevolution's capacity to increase biological productivity and ecosystem stability.
Because they are hidden from us, it's easy to underestimate how voluminous plant roots are, and what an important job they do. The root mass of a tree is around the size of the above ground growth but for perennial grasses the root mass can be four times greater than the above ground growth. While they are alive, plant roots add to the soil carbon by exuding more than two hundred carbon compounds, and when they die they add to the humus, both of which result in increased soil fertility. The way we treat the above ground bit of a plant has huge impacts on the roots.
In short Mr. Flannery is arguing for a quick change in how we manage our soils as we bring on methods to build a manufacturing infrastructure that can put carbon back in the soils.
