Trees: A Help, not a Cure, for Climate Change

June 4, 2022

Zeke Hausfather, the scientist’s scientist, has a piece on carbon capture in the New York Times. I’ll excerpt key points here.

Zeke Hausfather in New York Times:

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.

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.

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.

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.

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.

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