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.

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