A New Boost for Biochar as a Natural Climate Solution

TNC Science Brief

This carbon-stable product made by pyrolyzing crop residues could be a meaningful ally in tackling the climate crisis.  A recent study offers a new, best-in-class global map to evaluate and fully harness its potential.

The Gist

As we confront the urgent need to combat climate change at a global scale, scientists are continually searching for innovative solutions to reduce carbon dioxide (CO2) emissions and remove CO2 from the atmosphere. One such way is a little talked about natural climate solution (NCS) with huge promise: biochar.

Biochar is a type of charcoal made from pyrolyzing (heating to high temperatures in the absence of oxygen) leftover organic materials such as agricultural crop residues, and it’s an effective way to remove CO2 from the atmosphere because it lasts in the soil for longer than other biomass would, leading to more carbon sequestration. Biochar can also boost soil health and productivity; forms of pyrolyzed crop residues – sometimes referred to as dark earths – have used by societies around the world to build soil and crop health.

The Big Picture

Despite this potential, to date, knowledge on crop residue resources and their climate mitigation potential has been limited to country-level agricultural statistics.

“We know biochar has great technical potential as a natural climate solution,” says Stephen Wood, a co-author on the paper and senior scientist in agriculture and food at The Nature Conservancy. “One thing that has been missing are high resolution, location-specific maps of crop residue resources that could be used for biochar production.”

Researchers at the Swedish University of Agricultural Sciences, The Nature Conservancy, Cornell University, and Yale School of the Environment set out to solve this challenge. The resulting paper was published last week in the open-access sustainable energy journal GCB Bioenergy.

The study revealed that crop residue generates around 2.4 billion metric tons of carbon annually. If all crop residues were used for biochar production, the theoretical potential of climate mitigation could reach a maximum of one billion metric tons of carbon stored per year—equivalent to all emissions from the world’s crop production.

Even accounting for crop residues that are used for other purposes, like feeding livestock, the global biochar production potential for climate mitigation still amounts to around 510 million metric tons of carbon per year, with 360 million metric tons per year remaining sequestered in soil after a century.

As for the permanence of biochar—referring to how long the carbon can be stored in the soil – this varies by region but remains impressive, with a range of 60% to nearly 100% of the initial carbon remaining after 100 years.

The Takeaway

Twelve countries have the technical potential to sequester over one-fifth of their current emissions as biochar from crop residues, with Bhutan (68%) and India (53%) having the largest ratios.

There are still some fundamental issues surrounding biochar that need to be solved for this NCS to reach its full potential. These include how to produce the natural resource sustainably and how to distribute it.

“This paper doesn’t answer all of those questions,” Wood emphasizes. “But what is does provide is a new best-in-class data product related to the potential of biochar as a natural climate solution.”

The authors hope that the high-resolution maps of crop residue production and biochar sequestration potential will offer valuable insights to the scientific community, and support decision-making and investment related to biochar production. We need all solutions on the table, and biochar is another promising innovation we should leverage as we navigate the path toward a more sustainable and climate-resilient future.

Read the Paper

Karan, S. K., et al. (2023). Potential for biochar carbon sequestration from crop residues: A global spatially explicit assessment. GCB Bioenergy.

View paper