One of mankind's most ancient agricultural techniques, known as pyrolisis — essentially slow cooking agricultural waste like straw, corn stalks, and manure in a low oxygen environment resulting in biochar — is capturing the attention of scientists as a means to dramatically reduce the amount of CO2 entering the atmosphere.

Cities in the Amazon, like the fabled El Dorado, used biochar to create a thriving agricultural megapolis on top of infertile soil, and now the technology has been upgraded for 21st century applications. According to a new study by an international team of scientists, biochar could be one of the most effective means to dramatically reduce our carbon impact.

Pyrolyzers — the combustion chambers used to make biochar — can be made at all scales, from cookstoves in the developing world to mobile units for sustainable forestry management to industrial plants. Out of a waste product that was typically burned on the field (or left to decompose), the pyrolyzer creates a product with multiple benefits.

Biochar locks carbon into the soil for a thousand + years (thus qualifying as a carbon credit, though the verification system has yet to be solidified) while providing organic soil ammendements that builds soil structure, reduces fertilizers, and volumizes the soil which helps with moisture and nutrient retention. For farmers this means a productivity gain of 15%-220%.

It's about putting carbon back in the soil, where it belongs.

According to the report, biochar has the potential to mitigate 1.8 billion tonnes of CO2, or about 12 percent of the world's annual CO2 output using only waste biomass (the stuff we're currently just throwing away). And while all that cellulosic waste could be used to create ethanol — the report estimates cellulosic biofuels could alleviate 10 percent of CO2 emissions — the multiple benefits of biochar and the fact that it beats ethanol in CO2 mitigation gives it the leading edge.

Of course, both technologies are likely to be employed depending upon the resources and restraints of each agricultural bioregion, but either way, we will need many such "carbon-negative" solutions in the near future.

Yes, we need to do everything we can to reduce our carbon emissions as quickly as possible, but without technologies that actually pull CO2 out of the atmosphere, it's going to be a tough (and very hot) road into the 22nd century.

Shout out to Lopa Brunjes of the Carbon War Room for the tip on the report and the great photos.

Related on MNN: What is biochar?

Study reveals biochar as a strategy to fight global warming
Using agricultural waste to make biochar has the potential to reduce 12% of global CO2 emissions annually.