The ancient inhabitants of Amazonia knew how to keep fragile soils fertile—and may have hit upon a way to combat present-day climate change. That technique? Biochar, or any plant or animal waste turned to charcoal and put back into the ground.

Studies suggest as much as 900 million metric tons of carbon a year could be locked up this way—and improve the soil's ability to grow crops as well. That's nearly 20 percent of current CO2 emissions as a result of burning fossil fuels.

And a new study shows that biochar could have an impact on agriculture's other greenhouse gas emission: nitrous oxide, or laughing gas, which is no laughing matter when it comes to climate change. Biochar applied to Australian fields and left for a number of months cut such emissions by more than 70 percent, as well as preventing nitrogen and ammonia from leaching out of the soil in water. Such fertilizer leaching is responsible for dead zones across the world, like the one at the mouth of the Mississippi River currently.

Of course, biochar is no panacea, despite fans like Richard Branson. Some studies suggest biochar can accelerate microbes degrading organic matter into dread CO2 in places like the boreal forests of the northern hemisphere. But perhaps charcoal is better in soil than burned as fuel for barbecues. The terra preta soils of Brazil are still being farmed, centuries after the biochar was added.

—David Biello