21 Jan 2014

As Uses of Biochar Expand, Climate Benefits Still Uncertain

Research shows that biochar made from plant fodder and even chicken manure can be used to scrub mercury from power plant emissions and clean up polluted soil. The big question is whether biochar can be produced on a sufficiently large scale to slow or reverse global warming.
By mark hertsgaard

Biochar, the charcoal-like material sometimes touted as a miracle cure for global warming, might first gain economic traction as a weapon against local air pollution, research by the U.S. Department of Agriculture indicates. There is a catch, however: The biochar should be produced from chicken manure.

"We don’t know why, actually," says Thomas Klasson, a scientist at the USDA’s Southern Regional Research Center in New Orleans. Klasson has led a team exploring the potential of biochar to capture the mercury emitted when power plants burn coal. When deployed as a scrubber,
Jeff Hutchens/Getty Images
Biochar holds promise for sequestering carbon and cleansing polluted air.
biochar made from chicken manure "removed almost all of the mercury" from a simulated coal emissions stream, Klasson’s team found. "We tried biochars made from turkey manure, almond shells, and cottonseeds, but chicken manure is the best," Klasson says.

Biochar is produced when plant matter (leaves, trunks, roots), manure, or other organic material is heated in a zero- or low-oxygen environment. The carbon the organic material had previously absorbed via photosynthesis is thus captured in solid form; the resulting biochar can take the shape of sticks, pellets, or dust. When biochar is inserted in soil, the effect is to remove carbon from the atmosphere and store it underground, where it does not contribute to global warming. Biochar also brings agricultural benefits by boosting soil’s fertility and its ability to withstand drought or
Adding biochar to 10 percent of global cropland could sequester the equivalent of 29 billion tons of CO2.
flooding; it can also rid soil of heavy metals and other pollutants.

The largest outstanding question about biochar is how much of a difference it can make in slowing global warming and how soon. Johannes Lehmann, a professor of agricultural science at Cornell University and one of the world’s top experts on biochar, has calculated that if biochar were added to 10 percent of global cropland, the effect would be to sequester 29 billion tons of CO2 equivalent — roughly equal to humanity’s annual greenhouse gas emissions.

What researchers still don’t know is how long that buried carbon would remain sequestered from the atmosphere. Also unclear is just how much biomass would have to be turned into biochar to make a meaningful dent in global warming, and what environmental and social impacts this might have — for example, by encouraging the clear-cutting of forests and their replacement by plantations of trees destined for biochar production.

Lehmann and former NASA climate scientist James Hansen have emphasized that they oppose such plantations and other unsustainable practices as a means to produce biochar. Rather, Lehmann says, biochar should be sourced from the massive amount of waste materials that normal agricultural and forestry production methods leave behind: corn stalks, rice husks, tree trimmings, and the like. And as the chicken manure example described above illustrates, biochar could also help dispose of the large amounts of manure currently generated by poultry and livestock operations.

The case for extracting carbon from the atmosphere, via biochar or other methods, may get a prominent boost in April when the UN’s Intergovernmental Panel on Climate Change (IPCC) issues the next installment of its Fifth Assessment Report. A draft copy of the report by the IPCC’s Working Group Three, leaked last week, paints a grim portrait of the global failure to slow greenhouse gas emissions and says that if rapid action is not taken, severe climate and economic disruption will occur. As a
Biochar may enable us to essentially 'unmine coal and undrill oil,' says Bill McKibben.
result, future generations may well have to devise methods — possibly including the use of biochar — to remove CO2 from the atmosphere.

Some climate activists believe that biochar may offer a more environmentally friendly method of limiting global warming than do conventional forms of geoengineering, such as spraying sunlight-reflecting aerosols into the atmosphere. In the words of author Bill McKibben, founder of, biochar may enable us to "run the [climate] movie backwards … to unmine coal and undrill oil."

As the amount of carbon dioxide in the atmosphere climbs to 400 parts per million and beyond, and the impacts of climate change become more unmistakable and destructive — rapid melting of Arctic Ocean ice, a rising incidence of extreme weather events — the case for extracting carbon from the atmosphere becomes increasingly compelling. Reducing the world’s emissions of CO2 and other greenhouse gases — the focus of virtually all public discussion and government policy on climate at the moment — remains vital, but as a practical matter that effort only affects how quickly the 400 ppm figure will increase. Turning biomass into biochar and burying it underground effectively withdraws CO2 from the atmosphere; if done at sufficient scale and in combination with aggressive reductions in annual greenhouse gas emissions, biochar thus could help reduce atmospheric concentrations of CO2.

To date, the relatively high price of biochar has been a stumbling block to these ambitions, but biochar’s ability to cleanse contaminated air and soil could help overcome that obstacle. Klasson of USDA points to a rule the U.S. Environmental Protection Agency (EPA) issued in 2011 that sharply limits the amount of mercury that power plants and other industrial sources may emit. Mercury is one of the ten elements or chemicals of most serious public health concern, according to the World Health Organization, which advises that "even small amounts … may cause serious health problems" for the nervous, digestive, and immune systems, especially for fetuses and young
Biochar’s ability to remediate polluted air and soil accounts for part of China’s growing interest.
children. The EPA estimates that its rule will reduce by 90 percent the amount of mercury emitted by coal-fired power plants, the nation’s largest source of mercury pollution.

The EPA rule could thereby give rise to a sizable new market for biochar, suggests Klasson, which in turn would improve the economic viability of other utilizations of biochar. Writing in the Journal of Environmental Management, the USDA scientist calculated that the EPA mandate would create a potential market for 120,000 tons of biochar a year. Since U.S. production capacity for all uses of activated charcoal — a conventional alternative to biochar — is 197,000 tons per year, the EPA’s mandate could expand the effective market demand by roughly 50 percent. Such a dramatic increase in the scale of production for biochar would reduce per-unit production costs, lowering the price of biochar closer to what farmers and carbon markets could bear.

"What farmers will pay [for soil enrichment] is going to be the lowest economic value for biochar," says Kurt Spokas, a USDA research scientist based at the University of Minnesota in St. Paul. "But if we open up the market to include uses with higher economic value, such as mercury remediation or the production of black carbons for toner cartridges and lead pencils, we could make biochar a going economic enterprise."

Interest in biochar is especially keen in China. Although the USDA, through its Agricultural Research Service, had been the global leader in biochar research, China "far outspend[s] us now," says Robert Fireovid, who coordinates biochar research at the service.

Biochar’s ability to remediate polluted air and soil accounts for part of China’s interest. After decades of rapid industrialization and lax environmental regulation, about eight million acres of land — an area the size of Belgium — is too contaminated by toxic metals, fertilizer residues, and other pollutants to grow food, Wang Shiyuan, China’s vice-minister for Land and Resources, said in December. Beyond these extreme areas of contamination, 70 percent of China’s total farmland has experienced lower crop yields due to excessive fertilizer application and soil erosion, according to Meng Jun, the deputy director of the Liaoning Biochar
Biochar delivers the greatest agricultural benefits when it is applied to soils that are poor.
Engineering and Technology and Research Center at the University of Shenyang.

All this has endangered food security, long a hot-button political issue in China. Over the past three years, the nation’s imports of corn, rice, and wheat have skyrocketed. A succession of food safety scandals has also rocked China; in 2013, the Food and Drug Authority of Guangzhou, the mega-city in China’s hyper-industrialized south, revealed that 44 percent of rice samples it tested had dangerous levels of cadmium, a heavy metal that can harm the liver and kidneys and cause cancer.

Applying biochar to contaminated rice paddies can substantially reduce cadmium pollution, concluded a two-year study published in the journal BioResources. For the experiment, biochar made from wheat straw was ground into pellets 2 millimeters in diameter and mixed into soil in Jiangsu province that contained high levels of cadmium. The concentration of cadmium in the rice harvested from the test plots was reduced by 45 percent in the first year of the experiment and by 62 percent in the second year. Crop yields were not affected.

Biochar also could address a second environmental challenge in China’s rural areas — the countless heaps of straw, corn stalks, and other crop residues stacked around virtually every village. Farmers often burn this fodder, producing local air pollution and releasing greenhouse gases. Instead, converting the plant material into biochar would reduce such pollution, professor Jun has noted. In addition, when the biochar was added to soil, it improved crop yields more than chemical fertilizers did, with yield differentials reaching 15 percent for peanuts, 7.2 percent for soybeans, and 8.1 percent for potatoes.

The results in China cannot automatically be extrapolated to the rest of the world, however. "You must always remember that not all biochars are the same, and their effects will differ according to what kind of soil is being amended," said Spokas of the USDA.

Spokas claims to have the world’s most diverse collection of biochars; his lab boasts 225 different varieties, many of which have been sent to him by fellow researchers, entrepreneurs, and enthusiasts. Spokas and his colleagues are doing lab and field tests to determine the properties of the


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different varieties, including their effects on soil fertility, how stable various types of biochar are in different soils, and how much carbon the different biochars sequester.

As a rule, biochar delivers the greatest agricultural benefits when it is applied to soils that are poor, either inherently or because of pollution. "We’re finding that biochar as a soil amendment tends to be less useful here in the Midwest, because the soil is already so fertile," says Spokas. Biochar tends to deliver more benefits to "soils overseas, because [the soils] have often been leached of nutrients."

The big question remains biochar’s effectiveness in slowing or reversing global warming, and that can only be answered by further research and real-world experiments — something the Chinese, at least, seem to understand. After being briefed on biochar in 2010, China’s national leadership made biochar production part of the state Clean Energy program in 2011, according to Genxing Pan of Nanjing Agricultural University. Biochar research is currently being supported by the Chinese Academy of Sciences and the Rural Economic Commission, among other entities.

The U.S. government, by contrast, is winding down its biochar research. Congress has cut the Agricultural Research Service’s budget by 12 percent since 2010, said ARS’s Fireovid. "We’ve closed at least ten laboratories in the last three years," he added. "The long-term studies we think we need to do on biochar, we just can’t do. We lack the funds."


Mark Hertsgaard has reported on climate change for The New Yorker, Vanity Fair, Time, the BBC, and The Nation, where he is the environment correspondent. His books include Earth Odyssey and HOT: Living Through the Next Fifty Years on Earth. Previously for Yale e360, he reported on California's bold steps toward tackling climate change.

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Great article of biochar. The implications on climate change are exciting, but more detailed studies are needed.
Posted by Gerald Kutney on 21 Jan 2014

A nice article, thanks. The reference by Prof. Johannes Lehmann to 29 gigatonnes CO2 capture should be clarified to be an annual amount (that is very large). An analyst who has compared biochar with some other approaches is Prof. Tim Lenton, recently moved to Exeter University in the UK, has calculated similar potential large values in the future.

See Lenton, Timothy M. "The potential for land-based biological CO2 removal to lower future atmospheric CO2 concentration." Carbon Management 1, no. 1 (2010): 145-160 - which is not behind a pay wall, and has a lot of valuable detail and comparisons.

There should be no surprise that China has become the new leader in biochar. They have similarly taken over leadership in all the other renewable energy areas where the US once had a commanding lead. They have the funds, the need, and they know how to move fast.

Meanwhile, congress dropping the USDA budget, especially on biochar, is about as short-sighted as one can get. Oh well — the Chinese can export back to us much as they do almost everything else — because of the climate denier views of (at least one house of) our congress.
Posted by Ronal W Larson on 21 Jan 2014

My colleagues and I have been stressing for some time that remediation/pollution control applications may turn out to be the major drivers for biochar programs. So we're glad to see control of Hg and Cd highlighted in this piece!

For several years now we have been pioneering the use of biochars as low-cost adsorbents for use in water and wastewater treatment — particularly for control of pesticides and other synthetic organic pollutants, and for nutrient recovery and odor control.

My research has focused on the generation and application of high adsorbing chars made from local surplus biomass for chemical toxin control in decentralized water treatment serving rural/remote communities in the developing world. (See www [dot] AqSolutions [dot] org.)

It would be great to see a follow-up piece highlighting these and other applications of biochar in engineered systems for environmental and public health protection!
Posted by Josh Kearns on 21 Jan 2014

The Japanese, Australians, and Europeans are years ahead of the US in biochar work.

The one exception is in thermal conversion technology. CoolPlanet Energy Systems' pyro/catalytic, tank ready bio-gasoline, diesel or jet fuel from biomass at $2.00/gal, puts us ahead.

For a complete review of the current science & industry applications of biochar please see my 2013 Umass biochar presentation. How thermal conversion technologies can integrate and optimize the recycling of valuable nutrients while providing energy and building soil carbon. I believe it brings together both sides of climate beliefs. A reconciling of both God's and man's controlling hands.

Agricultural Geo - Engineering Past, Present & Future
Across scientific disciplines carbons are finding new utility to solve our most vexing problems

Posted by Erich J. Knight on 22 Jan 2014

The beneficial aspect of biochar has nothing to do with climate change! It can solve the issue of what to do with all of the organic waste that humans and farms produce. Stop talking about climate change. Let's talk about energy, soil remediation, and pollution control. Let's talk about closing the carbon cycle.
Posted by gordon cochrane on 22 Jan 2014

What this ultimately boils down to is plant growth and storage of plant carbon. Is it necessary to char this material before storing it? There is a carbon footprint associated with the energy expenditure for biochar production that must be figured into the equation.

I have often thought about the prospect of storing carbon underground in the form of woody material: trees. Wood is currently stored in an above-ground carbon sink in our structures and buildings. Could we expand on this sink, either above ground or below, thereby replacing much of the carbon being removed via fossil fuel extraction? This would have to be carefully managed using sustainable forest practices on lands that have already been cleared or harvested, but entire disturbed areas could be reforested for this purpose.

Biochar would have a space advantage for storage, however, the article states that it simply would be mixed with the soil, where eventually it would degrade and be re-released into the atmosphere through oxidation and incorporation into the carbon cycle. The benefits of biochar are real, including removal of toxins and for agriculture, but before we start mass producing it for the sake of absorbing carbon, the full range of plant production alternatives should be considered.
Posted by Ross Geredien on 23 Jan 2014

Excellent article on Biochar.

Biochar is a name for charcoal when it is used for particular purposes, especially as a soil amendment. Like all charcoal, biochar is created by pyrolysis of biomass. Biochar is under investigation as an approach to carbon sequestration to produce negative carbon dioxide emissions. Biochar thus has the potential to help mitigate climate change, via carbon sequestration. Independently, biochar can increase soil fertility, increase agricultural productivity, and provide protection against some foliar and soil-borne diseases. Furthermore, biochar reduces pressure on forests. Biochar is a stable solid, rich in carbon and can endure in soil for thousands of years. The burning and natural decomposition of biomass and in particular agricultural waste adds large amounts of CO2 to the atmosphere. Biochar that is stable, fixed, and 'recalcitrant' carbon can store large amounts of greenhouse gases in the ground for centuries, potentially reducing or stalling the growth in atmospheric greenhouse gas levels at the same time its presence in the earth can improve water quality, increase soil fertility, raise agricultural productivity, and reduce pressure on old-growth forests.

Biochar can sequester carbon in the soil for hundreds to thousands of years, like coal. Such a carbon-negative technology would lead to a net withdrawal of CO2 from the atmosphere, while producing and consuming energy. This technique is advocated by prominent scientists such as James Hansen, head of the NASA Goddard Institute for Space Studies, and James Lovelock, creator of the Gaia hypothesis, for mitigation of global warming by greenhouse gas remediation. Researchers have estimated that sustainable use of biocharring could reduce the global net emissions of carbon dioxide (CO2), methane, and nitrous oxide by up to 1.8 Pg CO2-C equivalent (CO2-Ce) per year (12% of current anthropogenic CO2-Ce emissions 1 Pg=1 Gt), and total net emissions over the course of the next century by 130 Pg CO2-Ce, without endangering food security, habitat, or soil conservation.

Biochar is a high-carbon, fine-grained residue which today is produced through modern pyrolysis processes. Pyrolysis is the direct thermal decomposition of biomass in the absence of oxygen to obtain an array of solid (biochar), liquid (bio-oil), and gas (syngas) products. The specific yield from the pyrolysis is dependent on process conditions, and can be optimized to produce either energy or biochar.

Biochar is a desirable soil material in many locations due to its ability to attract and retain water. This is possible because of its porous structure and high surface area. As a result, nutrients, phosphorus, and agrochemicals are retained for the plants benefit. Plants therefore, are healthier and fertilizers leach less into surface or groundwater.

Bio-oil can be used as a replacement for numerous applications where fuel oil is used, including fueling space heaters, furnaces, and boilers. Additionally, these biofuels can be used to fuel some combustion turbines and reciprocating engines, and as a source to create several chemicals. If bio-oil is used without modification, care must be taken to prevent emissions of black carbon and other particulates. Syngas and bio-oil can also be “upgraded” to transportation fuels such as biodiesel and gasoline substitutes. If biochar is used for the production of energy rather than as a soil amendment, it can be directly substituted for any application that uses coal. Pyrolysis also may be the most cost-effective way of producing electrical energy from biomaterial. Syngas can be burned directly, used as a fuel for gas engines and gas turbines, converted to clean diesel fuel through the Fischer–Tropsch process, or potentially used in the production of methanol and hydrogen.

Bio-oil has a much higher energy density than the raw biomass material. Mobile pyrolysis units can be used to lower the costs of transportation of the biomass if the biochar is returned to the soil and the syngas stream is used to power the process. Bio-oil contains organic acids that are corrosive to steel containers, has a high water vapor content that is detrimental to ignition, and, unless carefully cleaned, contains some biochar particles which can block injectors. The greatest potential for bio-oil seems to be its use in a bio-refinery, where compounds that are valuable chemicals, pesticides, pharmaceuticals, or food additives are first extracted, and the remainder is either upgraded to fuel or reformed to syngas (Wikipedia).

• The pyrolysis of forest- or agriculture-derived biomass residue generates a biofuel without competition with crop production.
• Biochar is a pyrolysis byproduct that may be ploughed into soils in crop fields to enhance their fertility and stability, and for medium- to long-term carbon sequestration in these soils.
• Biochar enhances the natural process: the biosphere captures CO2, especially through plant production, but only a small portion is stably sequestered for a relatively long time (soil, wood, etc.).
• Biomass production to obtain biofuels and biochar for carbon sequestration in the soil is a carbon-negative process, i.e. more CO2is removed from the atmosphere than released, thus enabling long-term sequestration.

Dr. A. Jagadeesh Nellore (AP), India

Posted by Dr.A.Jagadeesh on 28 Jan 2014

That's a nice article.
Posted by Esa Kurniawan on 07 Feb 2014

Regarding the question of persistence of biochar in the soil: oxidative half-life, if you will. The Terra Preta story should be informative. There are places in the Amazon rain forest with deep black soils based on biochar that came from many years of slash-and-burn agriculture. This traditional biochar is much more persistent than humic acid and other oxidized components of humus.
Posted by Roger Faulkner on 15 Feb 2014

An important factor is being overlooked or not directly credited in this article and discussion. When biochar is used as a soil amendment, it not only helps with water and fertilizer retention but it builds soil organic materials, sequestering more carbon and improving soil performance over time.
Posted by Henry Swayze on 06 Sep 2014

Are the editors of Yale e360 deniers?

The article title says that "the benefits if biochar are uncertain." Nonsense! The exact opposite has been shown for decades, as noted in the article itself!

Also, the subtitle right below this denier title claims: "The big question is whether biochar can be produced on a sufficiently large scale to slow or reverse global warming." In fact, it's been shown by Goreau, 2014, and others that the opposite is the case. Research is ongoing to nail down the scientific understanding of how soil carbon sequestration works.

Posted by robert dresdner on 23 Jun 2015

Excellent articles on Biochar. Incidentally not much is known or being done about converting the huge amount of organic wastes in Africa into Biochar. Burning increases the risk if CO2 emission and global warming. I and my small group are currently developing cheap and sustainable ways of producing biochar from these waste products and we surely need collaboration from around the world on how to fine tune our approaches. Keep up the good job.
Posted by Dr. Obi Udengwu on 29 Oct 2015

What the article does not mention and which I am not qualified to answer is what is the net reduction in carbon? To produce biochar you need some energy source to burn the organic materials in a low oxygenated environment. This expenditure of energy must come at some cost of carbon emmittance.
Posted by Chris on 10 Dec 2015

This topic gains importance after the Paris climate
deal because the final draft addresses carbon
sequestration directly in Article IV. The article says,
" accordance with best available science, so as to
achieve a balance between anthropogenic emissions
by sources and removals by sinks of greenhouse
gases in the second half of this century, on the basis
of equity, and in the context of sustainable
development and efforts to eradicate poverty." The
key word is "BALANCE" meaning that CO2 supply
from fossil fuels (coal included) is allowed if there is a
balance in CO2 demand, i.e. soil, plant and tree
sequester. This concept addresses the fact today >
3.5 billion live in abject energy poverty world wide.
The most efficient supply of electricity for them will
be coal. New research into carbon sinks like biochar
becomes paramount in the global climate search for
safety and equity.
Posted by JAMES MATKIN QC on 14 Dec 2015



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