Cocoa bean shells enter one end of a factory in the German port city of Hamburg and come out the other with an incredible black powder that may be used to counter global warming.

The process of making biochar involves roasting cocoa husks to 600 degrees Celsius (1,112 degrees Fahrenheit) in an atmosphere free of oxygen.

The procedure traps greenhouse gases, and the resulting material can be utilized as fertilizer or as a component of "green" concrete.

Even though the biochar sector is relatively young, scientists claim the technology offers a creative solution to remove carbon from the atmosphere of the planet.

The Intergovernmental Panel on Climate Change (IPCC) of the UN estimates that biochar has the potential to be used to capture 2.6 billion of the 40 billion tons of CO2 that humanity now produces annually.

However, expanding its use is still difficult.

Read: Cadbury faces child labor claims on its cocoa farms

CEO of Circular Carbon Peik Stenlund told AFP at the biochar factory in Hamburg that they are "reversing the carbon cycle."

One of the largest plants in Europe receives the spent cocoa shells from a nearby chocolate factory via a system of grey pipes.

The husks' CO2 is trapped by the biochar in a manner that can be applied to any other plant.

The carbon contained in the unused byproduct would be released into the atmosphere as it decomposed if the cocoa shells were disposed of in the usual manner.

Instead, according to David Houben, an environmental scientist at the UniLaSalle center in France, the carbon is stored in the biochar "for centuries".

"The equivalent of 2.5 to three tonnes of CO2" may be stocked in one tonne of biochar, also known as bio-coal, Houben told AFP.

Before being identified in the 20th century by scientists investigating incredibly fecund soils in the Amazon basin, biochar had already been utilized as fertilizer by indigenous communities in the Americas.

Because of the surprise substance's sponge-like structure, more water and nutrients are absorbed by the soil, which benefits crops. The factory in Hamburg is warmed by the heat produced by the installation's piping and enveloped in a slight chocolate scent.

The finished product is then dumped into white bags and sold to nearby farms as granules.

Silvio Schmidt, a 45-year-old farmer who raises potatoes west of Hamburg, near Bremen, is one of those who anticipate that the biochar will "give more nutrients and water" to his sandy soils.

Carbon cost

A certain amount of biogas is also produced throughout the production process, known as pyrolysis, and it is sold to the nearby plant. The plant uses 10,000 tonnes of cocoa shells annually to produce 3,500 tonnes of biochar and "up to 20 megawatt hours" of gas.

It is still challenging to scale up the production technique to the level the IPCC has in mind.

"To ensure the system stores more carbon than it produces, everything needs to be done locally, with little or no transport. Otherwise it makes no sense," Houben said.

Additionally, not all soil types can benefit greatly from biochar. According to Houben, the fertilizer is "more effective in tropical climates" but the raw components for its production are not widely accessible.

At "around 1,000 euros ($1,070) a tonne -- that's too much for a farmer," he said, the price can also be prohibitive.

Houben claimed that different uses for the potent black powder would need to be discovered. For instance, biochar might be used in the construction industry in producing "green" concrete.

However, the biochar industry has come up with another approach to make money: selling carbon certificates.

The plan is to market certificates to businesses seeking to balance out their carbon emissions by creating a specific volume of biochar.

The CEO of the company, Stenlund, stated that "we are seeing strong growth in (the) sector" as a result of the inclusion of biochar in the strictly controlled European carbon certificates system. In the upcoming months, his company plans to open three new locations to increase biochar production.

Biochar projects are expanding all over Europe. The biochar industry organization estimates that production will nearly double to 90,000 tonnes this year from 2022.