James Lovelock, remarkable for his just-in-time discovery of the ozone hole, and then for his fruitful Gaia hypothesis (that the Earth is a complex interacting system which self-regulates to preserve life), was recently interviewed on mitigation of climate change. At nearly 90, he pulls no punches. It is too late to contain carbon emissions, he says. Trying to sequester carbon dioxide in underground caverns is a waste of time, and there is little to be hoped for from alternatives to fossil fuel energy.
There is one way we could save ourselves and that is through the massive burial of charcoal. It would mean farmers turning all their agricultural waste -- which contains carbon that the plants have spent the summer sequestering -- into non-biodegradable charcoal, and burying it in the soil. Then you can start shifting really hefty quantities of carbon out of the system and pull the CO2 down quite fast.
What? And we've been agonizing over fossil fuel emissions, carbon tax, alternative energy and so on? We just have to bury charcoal? Let's examine this proposal, beginning with the carbon cycle.
Two of the greenhouses gases threatening the health of the biosphere as they accumulate in the atmosphere are carbon molecules - carbon dioxide and methane. Methane is 25 times as potent as carbon dioxide in its global warming action. The third main component of greenhouse gases is nitrous oxide (8% and 298 times as potent), which we will discuss later. Carbon in various forms resides in the deep layers of the earth; in the surface, biologically active soil; in the ocean, both deep and shallow levels; in the layer of plant and animal material on the surface of the earth; and in the atmosphere.
In the deep layers of the earth and of the ocean, there is little movement of carbon, except when humans unearth it as fossil fuels and send it into the atmosphere. Between the atmosphere and the shallow ocean, the soil and the living beings of the biosphere, there is continual exchange of carbon.
This is the carbon cycle. Our problem is that human activity has altered the carbon cycle in ways that have increased atmospheric carbon. Carbon dioxide and methane, together with water vapor and nitrous oxide, act to trap radiant sun energy near the Earth's surface. This is causing climate change.
The human activity contributing to this change is:
It looks as if our modes of growing food, feed for animals, fuel, and fibre are part of the problem. It's not only burning fossil fuels. Our forestry and agricultural methods need to be part of the solution. Stopping deforestation, returning land to ecosystem restoration, "no till" agriculture, new methods of grazing and animal management that mitigate the worst greenhouse gas effects, and especially organic methods of food production are important parts of problem-solving. These will all keep more carbon in the soil and in living organisms and less in the atmosphere.
But Lovelock and others suggest we can go much further in restoring carbon cycle proportions (between soil, living organisms and atmosphere) that support life as we know it. The idea is to turn agricultural waste, which otherwise would decay and release carbon to the atmosphere, into charcoal, which is highly concentrated carbon, and bury it. Carbon in this form is relatively non-biodegradable, and remains stable for thousands of years. It would be the equivalent of returning to the earth some of the carbon we've mined and put in the atmosphere.
This form of carbon is called "biochar." It is made by burning organic (mainly plant) material at a low temperature with little oxygen. Pre-Columbian Amazonians made biochar by burning plant material in pits covered with earth. They then mixed it with compost and soil to create what European colonists called "terra preta," or dark earth. They were not attempting to reduce greenhouse gases, so why did they do this?
Biochar has numerous benign properties the Amazonians made use of: it increases availability of soil nutrients, thus reducing the need for fertilizer and increasing productivity; it helps retain water; it reduces deforestation, because by converting from "slash and burn" to "slash and char," soil fertility remains satisfactory in a given site for much longer. And, it turns out, it decreases emissions of methane and nitrous oxide, the other greenhouse gases. In modern kilns, the manufacture of biochar can produce both oil and gas used for energy purposes. Several different technologies are under trial in low income countries to power cooking stoves and ovens, as well as to enrich soil. One type uses gas from the making of biochar to power cooking stoves. Another type uses small household stoves to both make biochar and cook food. These endeavors may increase human health by reducing indoor smoke from inefficient open wood fires.
Beyond soil enrichment needs, can carbon be buried in the earth at a scale that would make a difference to atmospheric carbon? According to Sara Scherr and Sajal Sthapit in the 2009 State of the World Report,
"There is a global production potential of 594 million tons of carbon dioxide equivalent in biochar per year, simply by using waste materials such as forest and milling residues, rice husks, groundnut shells, and urban waste. Far more could be generated by planting and converting trees..."
Advocates calculate that if biochar additions were applied at this rate on just 10 percent of the world's cropland (about 150 million hectares), this method could store 29 billion tons of CO2-equivalent, offsetting nearly all the emissions from fossil fuel burning.
Four cautions must be borne in mind: firstly that making biochar on this scale by modern methods would require enormous investment in kilns in all agricultural areas of the globe. Considering the many co-benefits, including poverty alleviation, this could be considered an excellent investment. There are many current projects running on exactly these assumptions (see sidebar boxes). One new idea is to use big microwave ovens. If biochar were made by the ancient methods, some of its benefits would be retained, but the potential for energy generation would be lost.
The second caution is that continued soil fertility depends on nutrients being returned to the soil that would be burned in biochar production. There is current research aiming to understand what proportions of plant material can be turned to biochar without incurring deficiencies. The New Zealand government has funded two professorships in biochar, one to pursue its behavior in soil, and one to study the process of turning plant material to biochar. The long-term soil fertility effects of modern biochar are not yet known.
Thirdly, the dynamics of charcoal-humus mix are not well understood. A ten-year experiment with buried carbon in boreal forests showed more rapid decomposition of humus and release of below-ground carbon in carbon dioxide, thus partially offsetting the benefits of biochar as a long-term carbon sink. In addition, it is not yet clear that modern biochar remains as stable as Amazonian biochar.
Fourthly, to produce enough biomass to make a difference to atmospheric carbon may mean land use conversion, for example, forest clearing in order to plant "energy crops."
Clearing of forests or grasslands to make way for energy crop monoculture results in large quantities of emissions, reduces future sink capacity and causes further collapse of ecosystems and the biodiversity on which we depend for climate regulation. As widespread freshwater shortages are predicted, the regulation of rainfall by healthy forests and soils becomes increasingly critical, and the allotment of water for irrigation of energy crops more unsustainable.
In addition, such land conversion may displace indigenous people from so-called "marginal lands."
Biochar has some prestigious supporters. Besides Lovelock, Tim Flannery, Professor of Earth Sciences at Macquarie University, Sydney, Australia and author of The Weathermakers said,
"Biochar may represent the single most important initiative for humanity's environmental future."
Now we must return to the third greenhouse gas, nitrous oxide. It is nearly 300 times as potent in climate change effects as carbon dioxide but is present in smaller quantities. Fossil fuel burning has resulted in a 6 or 7-fold increase in oxides of nitrogen (including nitrous oxide) in the atmosphere. Other increases have been caused by manufactured agricultural fertilizers (a major effect), burning plant material, and cattle management methods. Nitrous oxide not only acts as a greenhouse gas, but affects human health in two other ways. It depletes the ozone layer (thus causing skin cancer) in the upper atmosphere, and in the lowest layer of the atmosphere, it increases ozone concentrations (thus contributing to respiratory illness.) This is a pretty bad actor. How do we respond?
We need to stop burning fossil fuels and stop making artificial nitrogen fertilizers. Once again, organic horticulture practices come to the rescue. They greatly cut fossil fuel use in growing food, and entirely eliminate artificial fertilizer use. Biochar production would replace the high oxygen burning of plant material which sends nitrous oxide into the atmosphere.
Implications for the ordinary worried citizen:
Although burying biochar as a climate change mitigation project seems both closer to natural processes than other "geo-engineering" proposals, and has more long-term evidence behind it, there are still many unanswered questions about its sustainability. We need to watch closely as this knowledge emerges and to apply what is useful as soon as possible. The time is short. Let's hope the knowledge emerges soon.
In Egypt, over 20 million tonnes of rice straw are burned annually after the harvest, contributing to air pollution. The ash residue increases soil salinity, decreasing fertility. Researchers from the University of Mansura in Egypt and the University of Copenhagen are working on a rice straw gasifier which will produce fuel gas (syngas) and biochar. The gas will power flatbread baking ovens, and the biochar will be returned to the fields to increase soil fertility and water retention. This project will involve five villages.
The Mongolian Biochar Initiative is working with small-scale herders, vegetable growers, women farmers, and forestry workers at an individual and community level. The aim is to produce biochar to increase income, improve soil fertility, and combat global warming. They are using family-level low technology biochar production units based on feedstock common to rural Mongolia. The hope is to reduce desertification currently affecting the land. There is also the intention to make the stoves suitable for cooking and to replace current methods of using wood and dung for cooking and heating. The cleaner-burning stoves will also be introduced into urban areas where currently wood-burning causes serious smog in the winter months.4
Metta Spencer has pointed out the huge amount of wood biomass (living and recently living material) in trees destroyed by the pine beetle in western Canada and the US. Their conversion to biochar and use as soil amendment would be a big process that could be contribute significantly to mitigation of climate change and to impending unemployment with the global economic recession.
Joanna Santa Barbara is a peace and ecological activist, now contributing to the development of Atamai, a sustainable village in New Zealand which incorporates many of the recommended practices, including biochar and organic gardening.
1 Gaia Vince. One last chance to save mankind: an interview with James Lovelock, originator of the Gaia hypothesis. New Scientist Jan.21, 2009.
2 The International Biochar Initiative: www.biochar-international.org/projectsandprograms/9countryprojects.html
3 Sara J. Scherr and Sajal Sthapit. Farming and Land Use to Cool the Planet. In State of the World: Into a Warming World. 2009:Worldwatch Institute.
5 Wardle DA, Nilsson M-C, Zackrisson O. 2008. Fire-derived charcoal causes loss of forest humus. Science 320:629.
6 Ernsting A, Smolker R. Feb., 2009. Biochar for Climate Change Mitigation: Fact or Fiction? www.biofuelwatch.org.uk/docs/biocharbriefing.pdf. This is a major critique of what the writers call the "biochar lobby." They liken it to the intense and premature enthusiasm with which large-scale biofuel manufacture was adopted, only to have it recognized, some years later, that this is a serious ecological and economic mistake.