- The carbon storage capacity of forests is widely recognized as a crucial factor in curbing global warming and preventing climate catastrophe.
- But a new study finds that the future potential for forest CO2 storage is being overestimated, with global forest health (along with the ability of forests to go on storing carbon) vulnerable to increasing disturbances including wildfires, disease, pests and deforestation.
- Scientists argue that the very real threat of declining forest carbon storage capacity necessitates far faster decarbonization efforts, along with urgent action to monitor and conserve forests, and prevent widespread deforestation.
- Delaying action by as little as five years could incur huge economic costs and jeopardize climate goals, researchers found.
Banking on the capacity of global forests to continue storing huge amounts of carbon could put the Paris Agreement climate targets out of reach and incur huge economic costs. That’s the warning expressed in a new modeling study which finds the ability of forests to absorb and permanently store carbon dioxide is not a given, since a range of human activities are likely to degrade forest health (and carbon stores) in the future.
If forest health and sequestration are to be conserved, researchers say, emissions must be slashed now and forests must be aggressively protected.
Global forests currently absorb an estimated 7.8 billion tons of CO₂ annually — about a fifth of all human emissions. But, as the paper underlines, this ability is increasingly at risk due to a range of forest disturbances —including wildfires, droughts, changing weather patterns, pests and more — with many of these disturbances caused by humans or linked to a rapidly changing climate.
The paper, published in the journal NatureCommunications, concludes that postponing action to slash CO2 emissions, conserve forests, and end deforestation could jeopardize climate targets. On the flip side, “accelerated decarbonization could meet climate objectives despite forest carbon losses due to disturbances,” the authors write.
Michael Windisch, lead author of the paper and a researcher at the Potsdam Institute for Climate Impact Research, Germany, says humanity currently has a three-fold bet on forests: Relying on forest carbon storage to be permanent into the future, that the natural forest carbon sink will persist, and that this sink may even expand.
To be fulfilled, that “bet on forest carbon storage requires immediate attention,” he says. “This puts even more weight [on the idea] that we should safeguard and monitor forests to give us a bit of buffer in our mitigation targets.”
For Kristina Anderson-Teixeira, ecologist and leader of ForestGEO Ecosystems & Climate Program at the Smithsonian Tropical Research Institute in the U.S., the paper adds an important dose of reality to future estimates of forest carbon storage capabilities. She was not involved in the study.
“It’s making a very important point that I agree with fundamentally, that we’re tending to overestimate the ability of forests to sequester carbon because of neglecting disturbances,” she says.
Meddling with forest carbon
The researchers used data from four models to obtain their results — an integrated assessment model (REMIND-MAgPIE), a land- and water-use model, an energy-economy modelling system, and a global vegetation model (LPJmL) — to test how forest disturbances can affect mitigation goals and to assess the economic impact of mitigation.
Forests are accounted for in a variety of models, says Windisch, but many simulations tend to simplify the ability of forests to store carbon in the future. So the research team “meddled” with projected forest carbon storage by including various disturbances. They then compared business-as-usual results where action is delayed, with a foresighted conservation approach relying on immediate action to prevent carbon storage loss.
Concerningly, he continues, the team found that if forest carbon storage ability declines, it will result in a “high price to pay,” even if climate action is delayed by as little as five years. That high price is financial as well as existential, increasing the risk that the world blows by the emission reduction targets set by the Paris Agreement.
“If there were less carbon taken up by the forests [in years ahead, then] we need to take up the slack [now], basically in all other sectors,” he says. According to the team’s data, delayed action would be twice as costly and require twice as much effort to undo, and “take up the slack.”
That translates to a doubling in the carbon market price of each ton of CO2 absorbed, losses in annual GDP of up to 2.7%, and a requirement of much wider land-use mitigation efforts totaling an additional 149 million hectares (368 million acres) as compared to 69 million hectares (170 million acres) for a foresighted approach.
Delayed action would also likely require largescale deployment of a range of costly and risky carbon dioxide removal (CDR) geoengineering technologies, many of which remain highly speculative and small-scale at the present. Reforestation or afforestation are widely considered key low-cost, safe and potentially large-scale CO2 removal approaches.
If forest carbon sinks decline, “It could be feasible to not use these [geoengineering] technologies. But that would put even more pressure on all the other sectors,” says Windisch, which would require rapid simultaneous decarbonization of global energy, infrastructure and transportation.
Taking the proactive approach to addressing and curbing future declines in forest carbon storage proved a far better strategy. “The foresighted response to a potential forest carbon storage loss is so much easier, achievable, much less costly, [needing] much less effort than if we wait and delay action by just five years,” Windisch says.
Protecting forests, addressing climate
Current forest carbon storage models tend to ignore escalating human and climatic disturbances such as disease, drought and pests, while underestimating future levels of deforestation, and overvaluing CO2 fertilization, which increases photosynthesis rates.
“We don’t have perfect process-based projections of the forest carbon sink to date,” explains Windisch, noting that the advanced model his team created still couldn’t include all natural and anthropogenic disturbances. But the data seems clear: “It stands to reason … that we should be a bit cautious, and thus we should decarbonize a bit quicker. Otherwise, it’s going to be a tough awakening later on.”
Anderson-Teixeira agrees that current models are likely overestimating forest carbon storage in multiple ways. Work from her own lab has shown that certain optimistic assumptions (such as warmer spring times leading to greater forest productivity), don’t stand up to scientific rigor.
“It’s important to consider feedbacks — that as climate change worsens, the disturbance, or forest carbon loss, is going to be increasing in general,” she says. She points to the rising severity of wildfires and drought, and to research showing that increased storm severity causes more tree falls and forest mortality in the Amazon.
Jean Ometto, a senior researcher at Brazil’s National Institute for Space Research, who was not involved in the study, agrees that the new research highlights a problem with the overly rosy global view on the future effectiveness of forest carbon storage. “Tropical forests, for instance, which hold a large amount of carbon, seem to be in a declining capability of providing net fluxes of CO2 into effective and permanent stocks.”
To keep climate targets feasible and avoid large mitigation costs, Windisch says, humanity needs to increase monitoring and safeguard forests globally, taking a proactive route to conservation, thereby warding off the costs and climate risks of inaction.
“We also need to decarbonize quicker,” he adds, “so that we [will] be prepared to face a decreasing forest carbon sink, if it were to happen.”
Anderson-Teixeira says that protecting forests is crucial to reducing climate change risk, and so is research to better understand how forest health relates to carbon storage. The new study “highlights the fact that we need to reduce emissions aggressively, as opposed to relying on forests as a sort of magic bullet. That just isn’t a very realistic expectation.”
Banner image: The Pesalat Reforestation Project in Central Kalimantan, Indonesia. Humanity’s long-standing bet on the persistence of forest carbon storage capacity urgently needs to be reassessed, says study lead author Michael Windisch. Image by James Anderson / World Resources Institute via Flickr (CC BY-NC-SA 2.0).
Citation:
Windisch, M.G., Humpenöder, F., Merfort, L. Bauer, N., Luderer, G., … Popp, A. (2025). Hedging our bet on forest permanence for the economic viability of climate targets. Nat Commun 16, 2460 doi:10.1038/s41467-025-57607-x
FEEDBACK: Use this form to send a message to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.
