Not So Fast With The Biochar, Scientists Say

A new review of the scientific literature suggests the world step back and take a closer look before embracing biochar, the coal-like material created from biomass that many believe can remove carbon from the atmosphere while helping improve soils and crop growth.

The new study, published on the open-source and peer-reviewed site Plos One and highlighted by the Union of Concerned Scientists in a blog post, doesn’t go so far as to dismiss biochar‘s carbon-reducing potential. It does, however argue forcefully that there is little scientific certainty about the long-term greenhouse gas emissions implications of embracing it in a big way.


image via International Biochar Initiative

But let’s back up first and explain biochar, and to do that, let’s back up further and look at the whole growing and decomposing process.

Growing plants take up carbon dioxide, right? They then release that carbon when they decompose. It’s part of a natural, balanced cycle.

Enter biochar, in which biomass is subjected to high temperatures in a very-low-oxygen environment, a process called pryolysis. This rearranges the chemistry of the biomass to lock in the carbon. (Depending on how exactly the process is undertaken, it also releases oils and gases that can be processed into transportation fuels, or that can be used to fire the pyrolysis process in a kind of closed energy loop.)

So the net result of the plant growing and then being turned into biochar is a reduction in carbon in the atmosphere – along with all the other possible benefits. This is one reason why some scientists are very enthusiastic about biochar.

Advocates of biochar, like the International Biochar Initiative, also say that by plowing it into soils, it can also “be an important tool to increase food security and cropland diversity in areas with severely depleted soils, scarce organic resources, and inadequate water and chemical fertilizer supplies.”

But hold on, say researchers Noel Gurwick, Lisa Moore, Charlene Kelly and Pipa Elias:

Optimistic claims about biochar’s benefits to the environment contrast sharply with the limited amount of research on biochar’s behavior and effects. There is insufficient empirical evidence to support assertions that biochar amendment to soil mitigates climate change significantly, or that it provides overall environmental benefits when evaluated across a comprehensive set of metrics.

They also note that, “Even with limited available data, it is evident that potential long-term benefits of biochar-based carbon sequestration come at a cost of short-term CO2 pulses into the atmosphere and, consequently, near-term acceleration of climate change.”

Here’s how the Union of Concerned Scientists summed up the study:

Even though [the researchers] found 311 peer-reviewed research articles on biochar, the overwhelming majority were studies in the laboratory, not in soils under natural conditions. Of those 311, only seven actually estimated the decomposition rates of biochar in situ. And in those seven, the estimates of the “mean residence time” of biochar in the soil ranged from 8.3 to 3,624 years. That’s a pretty big range, to say the least. If biochar remains stable in soils for thousands of years, it can be an effective climate mitigation solution. But if we’re talking about less than a decade, it can’t.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.

  • Craigsams

    The median residence time in that meta analysis of the trials was in the 100s of years. We have a 30 year window to do something about rising greenhouse gas levels, More research is underway to measure the specifics and tree surgeons, arboriculturalists, cacao farmers and commercial vegetable growers are adopting biochar in various formats as a soil improver and, with coir or other growing media, as a peat replacement. The headline doesn’t do the research justice – they are calling for more research and there is more research being done, but biochar does no harm, often does good and undoubtedly retards the return of carbon to the atmosphere to some degree, greater or lesser.

    • Pete Danko

      Thanks for your comment. It’s interesting that you mention the narrow window we face in addressing rising GHG levels. In light of that, I’m curious what you think of this passage from the study: “Even in cases in which biochar additions to soil lead to GHG benefits over hundreds of years compared to alternative biomass management scenarios, approximately 50% of the biomass carbon will be released to the atmosphere as CO2 over the short term, either vented during pyrolysis or emitted when the other pyrolysis products such as bio-oil and syngas are combusted for energy. In contrast, the half-life of uncharred wood of northern temperate tree species ranges from 6.8 to 150 years, and wood decomposition proceeds gradually over that time period, avoiding a large, near-term pulse of CO2 to the atmosphere. Similarly, most wood products are long-lived. For example, wood used for single-family housing in the US has a half-life of approximately 80 years, again avoiding large pulses of CO2 to the atmosphere on time scales of weeks to years, although CO2 release associated with harvest and wood processing need to be taken into account. Therefore, in many cases charring woody biomass would lead to greater radiative forcing in the short term than would leaving it to decompose or using it in long-lived wood products.”

      • Craigsams

        I live in a house that was built in 1770. The oak frame and floors come from trees that were acorns around 1066. There’s no reason why they won’t be there in 300 years time if we keep the roof in good repair. Wood would be a much more common building material if the full carbon footprint of steel and concrete had to be an internalised cost, so I’m 100% supportive
        The EU subsidises the importation of trees and their burning as ‘green’ fuel – the huge Drax power station in Yorkshire gets fat subsidies to co-fire wood in their burners. That’s insane.
        Making bio-oil or syngas for energy generation using wood is also inefficient and depends on misguided subsidies.
        Making biochar as the primary goal of pyrolysis means that 60% of the carbon in woody feedstock is converted to biochar and the heat generated replaces fossil fuels. A sawmill, rice mill or coconut processing factory will us that heat to season sawn wood, dry unhulled rice or dessicate coconut meat. That’s an ideal, but not always achievable. The reality of wood harvesting is that almost half the harvested material is abandoned at extraction site and is leafy twiggy material that decomposes rapidly and the logs generate another 25% of waste being sawn into logs or whatever. That waste is either burned or rots quickly. A carbon tax that puts a realistic price on carbon will resolve most of these arguments – the maths will drive decision making instead of political responses to lobbyists. The methodology for calculating biochar carbon balance is now highly evolved. The Paris climate talks in 2015 should produce a global carbon accounting system that does not exclude farming or transportation (Kyoto’s big weakness) and will build on the commitment to carbon accounting that already includes California, the EU, Quebec, China, New England and other key players. Then biochar will take its rightful place in the palette of solutions to reduction of greenhouse gas emissions, along with wood as a building material, insulation, solar, wind and all the other technologies that are currently held back because oil companies balance sheets are showing assets that could become ‘stranded’ as demand for fossil fuels falls off a cliff.

  • Jud

    The study didn’t say to put the brakes on anything.

    It said there was not yet a systematic way of analyzing certain soil properties associated with it yet. Out of 311 studies only a handful addressed the issues they were looking at.

  • Duane Kaufman

    What’s with the ‘Like’ bar covering the article, making it hard to read?

    • Guest

      We’ve been seeing a few reports of this after our site crashed last week. What kind of browser and OS are you using?

  • Barry Batchelor

    Biochar is all about improving soil structure in low and medium quality soils. It’s ability to hold and exchange nutrient, hold moisture, reduce acidity, increase soil surface area and an expanding range of other benefits. I have been applying biochar in my own sandy acid soils for over 8 years now with amazing results.

    To much of the science to date has taken the wrong path with dealing with biochar and it’s application. Biochar should be blended with a nutrient source and applied each year as a normal soil improvement program. Applying 25 or 50 tonnes of straight biochar into any soil is just total nonsense and no farmer in his right mind could ever afford the bill to do this.

    You have to look at the wider picture of biochar. This is a product that can be made from biomass waste streams like milling waste, agri waste, urban waste. It’s production can be self fuelling with most technology producing excess heat and/or gas energy. It has been shown to hold leachable nutrients which will make lower rate fertilising more effective with environmental run off also reduced. I would also take a insider guess that biochar will become a major part of re-inoculating soil biota into much of the world’s over tilled and over sprayed conventional farming soils.

    Focusing only on bioochars greenhouse reducing potential is nonsense, find me a farmer, landscaper or gardener who would apply a product that only reduces greenhouse emissions??

    • Pete Danko

      I’m not saying that biochar can’t or shouldn’t be used to enhance soils — go for it. The question is whether it can be relied upon to reduce GHG emissions, as some believe.