An old tree trunk shows how burying wood can combat climate change

In 2013, Ning Zeng came across a very old, very important protocol.

At that time, he and his colleagues were digging a trench in the Canadian province of Quebec. They planned to fill it with 35 tons (39 US tons) of wood. Then they covered the wood with clay soil and left it to sit for nine years. The goal? To show that the wood will not decompose.

If it worked, this exercise would prove that burying plant material could be a cost-effective way to store carbon. Preventing this carbon from entering the atmosphere could help combat climate change.

But while digging the trench, Zeng’s team came across a pristine, twisted tree trunk. It was very old – older than anything they could have made in their experiment.

“I remember standing there and just staring at it,” Zeng says. He is a climate researcher at the University of Maryland in College Park. He remembers thinking, ‘Wow, do we really need to continue our experiment?’ The evidence is already there – and better than we could have done.”

The exposed tree trunk was once part of an eastern red cedar. About 3,775 years ago, this tree absorbed carbon dioxide (CO).₂from the air and then used its carbon molecules to make wood. When the tree died, it was buried under just two meters of clay soil.

It now turns out that this barrier allowed the tree trunk to retain at least 95 percent of its carbon. Zeng and his colleagues reported their results on September 24th Science.

“Scientists and entrepreneurs have long thought about burying wood as a climate solution. “This new work shows that it is possible,” says Daniel Sanchez. An environmental scientist at the University of California at Berkeley, he did not take part in the study.

“Durable and cost-effective climate solutions like these hold great promise for combating climate change,” he says.

Burial: a practical suggestion

New solutions to climate change are urgently needed. Reducing greenhouse gas emissions is not enough to achieve atmospheric CO2₂ levels to slow global warming. And by 2060, around 10 billion tonnes more carbon will need to be removed from the atmosphere and stored every year.

Through their growth alone, plants store the carbon of around 220 billion tons of CO₂ every year. But much of this carbon is released back into the air as plants die and decay. Stopping just a fraction of this collapse by burying wood might help. However, this strategy relies on finding conditions that prevent air, water and microbes from breaking down hidden carbon for long periods of time.

The newly discovered ancient protocol gives researchers a clue.

Zeng now suspects that the clay cover helped prevent oxygen from reaching the tree trunk, even though it wasn’t buried very deeply. “This type of soil is relatively common. You just have to dig a hole a few meters deep, bury wood and it can be preserved,” he says.

Burying wood could cost as little as $30 to $100 per ton of CO2₂the researchers estimate. This simplicity and low cost make wooden vaults more practical than other carbon capture techniques, Zeng adds. For example, a technology to capture carbon directly from the air costs $100 to $300 per ton of CO₂.

Underground wooden vaults

This diagram shows the structure of a planned wooden vault. In this arrangement, buried wood lies beneath a layer of clay soil. This soil then prevents oxygen from reaching the wood, helping it retain its stored carbon.

It is not yet clear whether scientists can recreate the conditions that preserved the Canadian tree trunk. But if so, this method could store up to 10 billion tons of carbon every year.

Even though Zeng’s team found the old tree trunk, they carried out the planned experiment. You are now completing the analysis. What they learn will help demonstrate best practices for storing carbon in buried wood.

But the tree trunk itself shows the promise of wooden vaults, Zeng says. “We now have the evidence to say, ‘Yes, it’s ready to be implemented.'”