Let's Not Pretend Planting Trees Is a Permanent Climate Solution

Let’s Not Pretend Planting Trees Is a Permanent Climate Solution
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 gases 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.
It is also increasingly likely that the world will pass 1.5 degrees Celsius — our most ambitious climate target — in the next decade or so. In the recent IPCC report, more than 96 percent of scenarios that limit warming to 1.5 degrees Celsius above preindustrial levels by the end of the century overshoot it on the way there. Once we overshoot 1.5 degrees Celsius, even getting emissions all the way down to zero will not cool the world back down. This is the brutal math of climate change, and it means that the only way to bring global temperatures back down in the future is through the large-scale removal of carbon dioxide from the atmosphere.
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.
While carbon removal is often conflated with carbon offsets, the vast majority of offsets currently sold pay someone else to avoid emissions rather than removing carbon dioxide from the atmosphere. Offset markets are plagued byhot air, 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. In one case, an environmental group even provided offsets that were sold to oil companies, making the dubious claim that they would otherwise allow the forests they own to be logged.
Permanent removals, on the other hand, are harder to game. There is little market value to permanently removing carbon dioxide from the atmosphere, so it is much easier to prove that money spent actually results in removal. And the risk of accidental rerelease is orders of magnitude smaller. That’s why the well-respected Science Based Targets initiative only allows measures that permanently remove carbon from the atmosphere to offset remaining emissions — and only alongside deep emissions reductions.
The private sector can help jump-start permanent removals by purchasing them today. For example, Frontier — a recently announced initiative — will purchase nearly $1 billion of permanent carbon removal over the next nine years to help support early-stage technologies and figure out what approaches work and can scale in decades to come. But voluntary investments by the private sector can only take us so far; ultimately, removing carbon from the atmosphere will have to be incentivized by government policy, either through a price on carbon or subsidies for carbon removal.
The scale of permanent carbon removal that will be needed to meet our most ambitious climate goals is staggering, compared to the small amount of removal that has taken place to date. We are playing catch-up here, as we are on many climate fronts. We need to use this decade to figure out what works and what can scale in the decades to come: experimenting with a wide variety of approaches like direct air capture, enhanced rock weathering, ocean alkalinity enhancement, biomass carbon removal and storage, and ocean biomass sinking among others.
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.
Zeke 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.