From sequestering carbon to boosting food production, there have been a lot of big claims made for biochar. So what's the deal?
In fact Albert Bates, author of The Biochar Solution, questioned his publisher's choice of title, suggesting that The Biochar Partial Solution might have been more accurate. Meanwhile George Monbiot issued a withering takedown of some of the grander claims being made by biochar advocates, pointing out that large-scale biochar production could have massive impacts on land use, biodiversity and social justice. And more recently Almuth Ernsting revisited the biochar issue, arguing that research on everything from positive impacts on crop yields to long-term soil carbon sequestration was questionable at best:
Biochar is also promoted as a way of improving crop yields. Those claims, too, are contradicted by science. Field studies reveal highly variable impacts. A recent synthesis review found that in half of all published studies, biochar had either no effect on plants or more worryingly, even suppressed their growth. The author cautioned that due to possible ‘publication bias’, the reported success in 50% of cases should not be taken “as evidence of an overall biochar likelihood of producing positive impacts”.
It certainly seems like the kind of global-scale "biochar as geoengineering" schemes being touted a few years back deserve a healthy dose of skepticism, and according to Ernsting at least, much of the political backing for global biochar initiatives has begun to fade away.
And yet interest among greenies and permaculturists remains high.