If there’s one mantra that has anchored the environmental movement since its inception, it’s that trees are good. Good for the environment. Good for biodiversity. And definitely good for the climate. Despite decades of high-tech effort (and a $100 million XPrize funded by Elon Musk), trees remain one of the most reliable ways to remove carbon dioxide from the atmosphere—to the tune of about 8 gigatons a year according to a 2023 study. So what’s with this paper just published in Nature by environmental non-profit World Resources Institute (WRI), stating that wood consumption accounts for about 10% of the world’s annual greenhouse gas emissions? That’s more than all the planet’s passenger cars combined. And the world is on track to harvest 50% more wood by 2050. Could this shake our faith in wood’s role as a climate hero? As ever, the devil is in the details.
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1. No accounting for waste. One problem pointed out by the WRI researchers is that the wood industry often fails to properly account for carbon emissions associated with harvesting wood. These include burning leftover logs and wood pellets for fuel and the rotting branches and roots that release carbon into the air when they decompose. “The bottom line is you got a lot of emissions coming from wood harvest, and we don’t pay attention to that,” Tim Searchinger, one of the paper’s authors, told Grist.
2. A surprisingly large carbon footprint. There’s another accounting trick that plays against wood, says Searchinger. Many certification schemes treat any use of wood as carbon neutral if it comes from forests that are managed “sustainably.” But that’s not so easy to pin down. A popular definition of sustainable management is matching annual harvest to annual tree growth, essentially keeping the size of the forest constant.That’s obviously better than clear-cutting, but it doesn’t mean that all the wood cut down is necessarily carbon neutral. “What that misses,” Searchinger told Heatmap, “is that if you didn’t harvest it, the forest would grow and absorb carbon. You’re keeping that added growth from happening.” Overall, the WRI researchers calculate that wood harvesting generates between 3.5 and 4.2 gigatons of carbon each year.
3. A mass of timber issues. The architectural world has gone all-in on mass timber projects—using engineered wood panels and beams in skyscrapers instead of carbon-belching concrete. But in another recent paper, Searchinger crunched the numbers on the real-world impact of switching from concrete to wood. To make that shift on a global scale, he thinks, will involve either raiding or replacing trees from natural forests. In either case, there’s a steep carbon cost. If those new forests are only managed as well as today’s forests are, mass timber would actually increase the carbon footprint of building projects.
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1. Branching opinions. Not so fast, say other forest scientists. In the Heatmap story, Austin Himes, an ecologist at Mississippi State University, says that there’s good evidence that removing timber and plants can actually make the remaining forest more resilient and enable it to suck up more carbon. Another result of thinning is reducing the risk of a devastating wildfire putting all that carbon up in smoke. There have also been numerous studies concluding that mass timber structures do reduce carbon emissions, possibly by as much as 25%.
2. Measure twice, cut once. One thing all the scientists agree on is that wood is a finite resource that we should be using more thoughtfully and efficiently. Solutions start in the forest itself. About 40% of wood intended for lumber and paper still ends up being burned for waste rather than being made into useful products, while improving logging techniques in the tropics could reduce logging emissions there by nearly half, according to The Nature Conservancy. Trees can also be planted alongside crops, reducing run-off, moderating extreme temperatures, and improving yield, all while storing carbon.
3. Pulp, read, repeat. Wood is one of the most recyclable materials in nature. German researchers have found that about 25% of wood from dismantled buildings could be reused directly, and about the same again could be processed into innovative construction products like wood wool cement board. Even humble paper has a long economic afterlife: paper fibers are used an average of 2.4 times around the world— and over six times in the US.
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What To Keep An Eye On
1. Lab-grown wood. What if you could produce a lot more wood without a lot more land? MIT researchers have grown wood-like plant tissue in a lab without any soil or sunlight. Other research involves making composite wood materials that continue to capture carbon even after the trees are cut down and gene-editing trees to produce 40% more pulp.
2. Rules about whether wood is really renewable. Earlier this year the EU voted to keep burning woody biomass for energy in its race to phase out coal by 2030. That puts it on a playing field with wind and solar power, allowing member countries to subsidize it. The Brussels-based forest protection campaign group Fern says the subsidy setup is insane as it means “EU citizens are paying energy companies to burn forests in the midst of a climate and biodiversity crisis.” Some EU representatives are now pushing for that rule to be modified or overturned.
3. Wood alternatives. Other plants can provide similar materials to wood, without requiring as much time or space. Bamboo is a fast-growing crop that can sequester tons of carbon per hectare per year, says carbon non-profit Project Drawdown, and can be made into paper, building materials and possibly even liquid biofuels. There are also companies already selling resilient, low-carbon “hempcrete” building blocks made from cannabis’s tamer cousin.
Image based on original byIgor Kopelinsky