Opinion | Let’s Not Pretend Planting Trees Is a Permanent Climate Solution

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By Zeke Hausfather

Dr. Hausfather was a contributing author to the IPCC Sixth Assessment Report. He is the climate research lead at Stripe and a research scientist with Berkeley Earth.

Trees are our original carbon removal technology: Through photosynthesis, they pull carbon dioxide out of the air and store it. They have lately been touted as a climate savior, a way to rapidly reduce the carbon dioxide that has accumulated in the atmosphere as we cut our emissions. A “trillion trees” initiative was launched with much fanfare at the World Economic Forum in Davos back in 2020, and it was one of the few climate solutions embraced by the Trump administration. Planting trees and protecting forests are a major part of many corporate efforts to offset emissions.

But there’s a catch. Carbon dioxide removed from the atmosphere is only temporarily stored in trees, vegetation and soil, while a sizable part of our emissions today, will remain in the atmosphere, much of it for centuries and some of it for millenniums to come.

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.

We have a saying in the climate science world: “Carbon is forever.” Around 20 percent of the carbon dioxide we put into the atmosphere today will still be in the atmosphere many thousands of years from now. This means that to effectively undo emissions, the carbon we take out of the atmosphere needs to stay out. There is a real risk 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. For carbon to be permanently removed by planting trees, forests would have to remain in place for thousands of years. On top of that, the trees would have to be planted on land that would have been forest-free for those same thousands of years had the trees not been planted.

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.

There is another option for removing carbon dioxide from the atmosphere. Our current emissions come primarily from burning fossil fuels that spent millions of years underground before being dug up. If we put carbon back into the ground, put it into deep oceans or turn it into rocks, we can keep it out of the atmosphere for tens of thousands of years, effectively counteracting the long-term impact of our current emissions.

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. (I recently joined the team at Stripe Climate to help support early-stage technologies and build a market for permanent carbon removal.)

In the recent Intergovernmental Panel on Climate Change (IPCC) report, my co-authors and I found that society needs to rapidly reduce emissions over the coming decades to avoid potentially catastrophic changes to our climate. We also showed that removing carbon dioxide already in the atmosphere would be an “essential element,” alongside rapid emissions reductions, to meet our climate goals.

How much carbon removal will ultimately depend on how quickly and fully we can cut emissions. Most of our models show that to keep warming below 1.5 degrees Celsius, we’ll need to remove around 6 billion tons of carbon dioxide from the atmosphere each year by 2050 — a bit more than annual U.S. emissions today. Over the next 80 years, we may need to remove more than 600 billion tons, an amount greater than 15 years of current global emissions.

Why will we need so much carbon removal? The science is clear that to stop the world from continuing to warm, we need to get emissions to “net zero.” But there will always be some remaining emissions and some greenhouse gasses will be extremely difficult and costly to fully eliminate. Our models suggest we will need at least a few billion tons of carbon removal each year to counterbalance the remaining hard-to-eliminate emissions. Emerging technologies have the potential to meet this need.

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