Plant trees, sure. But to save the climate, we should also cut them down

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(CNN) — Democrats have set their sights on passing major climate legislation, but with a razor-thin majority in Congress, they need to look for common ground with Republicans.

One of the most promising ideas is to plant a vast number of trees -- and also to cut them down.

President Joe Biden has announced an ambitious goal of net-zero emissions by 2050. That would mean switching to renewable energy, expanding public transit, retrofitting buildings, and a host of other policies to slash greenhouse gas emissions. But even in the best-case scenario, it won't be possible to eliminate all emissions. The idea of "net-zero emissions" is that any remaining emissions can be fully offset by so-called "negative emissions" -- methods of sucking carbon out of the atmosphere.

Planting trees is the most straightforward way to do that. Trees absorb CO2 for photosynthesis and store it as cellulose and lignin, the main components of wood.

Planting trees may also be the most popular climate policy. Even former President Donald Trump loved the idea. He championed an international initiative to plant 1 trillion trees, which would be enough to soak up at least a decade of global emissions. When Republican Rep. Bruce Westerman, a professional forester, introduced the "Trillion Trees Act" last year, he was joined by a bipartisan group of co-sponsors that included House Republican leader Kevin McCarthy.

According to the World Resources Institute, the US alone could add 60 billion new trees to deforested lands, agricultural or urban areas, and sparse eastern forests that aren't prone to wildfires.

Forests in the western US, on the other hand, are prone to wildfires, and that calls for putting down the shovel and reaching for the axe.

Wildfires turn trees from asset to liability. Last year's record blazes in California belched twice as much CO2 as the entire state's power plants. It's one of the terrible feedback loops of climate change, where wildfires beget more wildfires.

To break the cycle, it's often necessary to sacrifice individual trees for the good of the whole forest. If large trees are packed densely together, flames can spread easily between them, so "selective thinning" can reduce the risk of large fires. The same goes for small trees, which can act as "ladder fuel" by transmitting fires from the forest floor up to the treetops. Dead trees that are still standing, dried out like matchsticks, pose another fire hazard that can be neutralized with chainsaws.

Selective thinning can also help stop the spread of diseases and insects that, like fires, destroy millions of acres of US woodlands each year. Think of it as social distancing for trees.

Of course, some trees will still die even if they don't go up in smoke or fall prey to a fungus. Normally, their carbon content would return to the atmosphere in the process of decomposing, but here again, logging offers a solution. Mature trees can be felled while they are healthy, the wood can be put to good use, and new trees can be planted in their stead, effectively multiplying the carbon absorption potential of a given piece of land. (To be clear, this is an argument for increasing sustainable logging, not for cutting down every healthy tree and removing it, which could have serious impacts on the forest ecosystem.)

The environmental benefits of wood are not only in the carbon it stores. Wood can often substitute for construction materials that take significant emissions to produce, namely steel and concrete. It can also be burned to substitute for fossil fuels, though ideally using only low-quality logs and sawmill "scrap wood" that would otherwise be left to rot. In total, one study found, expanding the market for wood could decrease net global emissions by as much as 31%.

An additional opportunity the study didn't consider is charcoal. The process of converting wood into charcoal releases some carbon, but what remains is extremely stable and won't decompose for thousands of years. Scattering that charcoal on fields (sorry, barbecue lovers) helps the soil retain nutrients and prevents contaminated soil from leaching chemicals, all the while keeping carbon out of the atmosphere.

Beyond these practical uses, wood can also serve purely as a long-term carbon storage device. The key to locking away the carbon is to cut off the oxygen supply to microbes, thereby preventing decomposition.

Natural experiments show how this can be done. 19th-century lumberjacks in the US and Canada frequently stored logs on the surfaces of the Great Lakes or floated them down rivers, some of which ended up sinking along the way. These have remained in such good condition that a modern-day cottage industry has arisen to recover the logs and turn them into everything from hardwood floors to violins. New Zealand has a similar industry with logs that were fortuitously buried in swamps as long as 60,000 years ago.

Based on such examples, scholars have proposed chopping down trees or collecting fallen logs and intentionally stowing them away. That could mean sinking them to the bottom of lakes, interring them in abandoned mines or burying them in specially dug trenches.

The idea hasn't gotten much traction yet, but in 2013, the Quebec Ministry of Agriculture, Fisheries and Food funded a pilot project to dig a trench and bury 35 metric tons of wood. The project came to about $29 per metric ton of CO2 sequestered, according to government scientist Ghislain Poisson, in in line with a theoretical estimate of $10-$50.

That is cheaper than most high-tech forms of carbon capture and storage, which usually involve machines that filter carbon out of the air and pump it underground. Sequestering carbon at the typical power plant, where emissions are highly concentrated, runs to $30-$91 per metric ton of CO2, but in open air, which is the holy grail, costs theoretically range from $94-$232. To help this promising new technology get off the ground (or rather, into the ground), the federal government offers a tax credit of about $35 for every metric ton of CO2 removed in industrial carbon capture and storage. It's a policy that has enjoyed strong bipartisan support for over a decade.

Such innovation is certainly worth supporting, but while companies scramble to literally reinvent the tree, lawmakers can do more to support the real thing, which is cheap and ready to use now.

For starters, the US should plant billions of trees, which can remove CO2 from the atmosphere at a cost of only $10 per metric ton. It should step up selective thinning to prevent the spread of wildfires, diseases and pests. In addition, Congress should put a price on carbon -- a policy long opposed by most Republicans -- or offer other incentives to promote wood products and wood-based carbon capture and storage. Of course, any incentives must be paired with appropriate regulations, or else forest ecosystems could become collateral damage in efforts to protect the environment.

Climate change may be nature's revenge, but nature has provided a powerful tool for fighting it. For the benefit of future generations, let's plant trees -- and cut them down, too.

This story was first published on 'Plant trees, sure. But to save the climate, we should also cut them down'