Tree planting is not a solution to the climate crisis

“Trees can quickly and cost-effectively remove carbon from the atmosphere today. But when companies rely on them to offset their emissions, they risk merely hitting the climate ‘snooze’ button, kicking the can to future generations who will have to deal with those emissions.”

That’s climate scientist Zeke Hausfather, writing in a recent article in the New York Times.

Hausfather notes that about 20% of the carbon dioxide we put in the atmosphere today will still be there thousands of years from now. Meanwhile, the carbon dioxide removed from the atmosphere and stored in trees, vegetation, and soils is only temporarily stored.

Carbon is forever

He links to a 2008 article published in Nature Climate Change titled “Carbon is forever”, written by Mason Inman.

Inman quotes from a book written by David Archer, “The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth’s Climate”:

The lifetime of fossil fuel CO₂ in the atmosphere is a few centuries, plus 25 percent that lasts essentially forever. The next time you fill your tank, reflect upon this.

The climatic impacts of releasing fossil fuel CO₂ to the atmosphere will last longer than Stonehenge. Longer than time capsules, longer than nuclear waste, far longer than the age of human civilization so far.”

Hausfather points out that effectively undoing emissions means keeping removing carbon from the atmosphere permanently. “There is a real risk,” he writes, “that, in a warming world with more wildfires, with pests preying on trees and with drying soil, carbon in tree plantations could end up back in the atmosphere sooner rather than later.”

Permanently removing carbon by planting trees would mean that the trees have to survive for thousands of years. The trees would have to be planted on land that otherwise would have been free of trees for thousands of years. Obviously, that’s a counterfactual that’s completely impossible to verify.

Hausfather raises another problem with using offsets from tree planting to justify continued pollution:

Companies using trees to offset their emissions often sign a 40-year contract. But the companies selling and buying carbon credits may not be around in 40 years. There is a real risk that no one will be left holding the bag if tree plantations are clear-cut for development, go up in flames or are devoured by mountain pine beetles a few decades hence. In short, the timelines over which carbon removal needs to occur are fundamentally inconsistent with the planning horizons of private companies today.

Carbon removal

In March 2022, Hausfather joined Stripe Climate “to help support early-stage technologies and build a market for permanent carbon removal”. In his New York Times article, he writes about carbon removal – putting carbon back into the ground, into deep oceans, or turning it into rocks:

There are only a handful of facilities in Europe and North America that are currently doing permanent carbon removal; the technologies have been deployed outside the lab for less than a decade, and they are still quite expensive, with prices typically in the hundreds of dollars per ton of carbon removed. But a growing number of scientists are working toward scaling them up and reducing costs.

Hausfather was a contributing author to the recent Intergovernmental Panel on Climate Change Sixth Assessment Report. The report found that rapidly reducing emissions is crucial to avoid climate breakdown. Removing CO₂ already in the atmosphere is also an “essential element”.

To date, carbon removal efforts by companies and governments have largely relied on trees and soil. But even under a best-case scenario, these can only provide around half of the removal needed. We only have so much available arable land in which to plant the number of trees we need to store enough carbon.

Carbon offsets

Hausfather notes that the vast majority of carbon offsets involve paying someone else to avoid emissions, rather than actually removing CO₂ from the atmosphere. “Offset markets are plagued by hot air,” he writes, “with many actors gaming the system by claiming carbon credits for actions they were already planning to take, such as building a clean energy project or not cutting down a forest they own.”

He acknowledges that the scale of carbon removal necessary to address the climate crisis is “staggering” compared to the tiny amount of carbon removed so far.

Hausfather concludes that,

To tackle climate change, we need to reduce emissions as quickly as possible. But we also need to invest in bringing down the cost of technologies to remove billions of tons of carbon dioxide from the atmosphere in the future. Trees and soil are not a panacea for removing carbon. While governments should be encouraged to enhance the amount of carbon stored in trees, plants, and soil, we should be skeptical of claims that rely on temporary removals to justify additional “forever” emissions.

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