Forests have been quietly cooling the planet for decades, but their role is increasingly under threat.
Forests have historically acted as a reliable planetary thermostat. They regulate Earth’s temperature by removing carbon dioxide (CO2) from the atmosphere and locking it in trees, roots and soil — carbon that is emitted if trees are cut down. In a typical year, forests and other vegetation absorb roughly 30% of the carbon that humans emit from burning fossil fuels — a vital climate service performed at virtually no cost by trees around the world, from tropical rainforests to temperate and boreal forests.
But the past several years have been anything but typical.
New analysis of data from WRI’s Global Forest Watch (GFW) and Land & Carbon Lab reveals that extreme fires caused forests to absorb far less carbon than usual in 2023 and 2024, weakening their cooling effect. During those years, forests absorbed only a quarter of the carbon dioxide they do in an average year. 2023 marked the lowest “forest carbon sink” in over two decades when considering the loss of trees’ stored carbon and greenhouse gases caused by burning.
This recent sharp drop is also part of a longer-term decline, where the margin between forest emissions and carbon removals appears to be narrowing. With emissions from deforestation and other forest disturbances rising, the world’s forests risk shifting from a carbon sink to a carbon source.
Losing the world’s forest carbon sink will have catastrophic consequences for people and the planet. Without urgent intervention, a continued decline in forests’ ability to absorb carbon could accelerate climate change, increase the frequency of deadly extreme weather events, and disrupt rainfall patterns that underpin water and food security.
Tracking Emissions and Removals in the Forest Carbon Ledger
A quarter century of data shows that more than 80% of forest-related emissions stem directly from human decisions to clear trees, whether for pasture, farms, minerals, infrastructure or timber.
Over the past 24 years, the dominant driver of forest-related emissions has been agriculture, accounting for just over half (53%) of emissions from all tree cover loss from 2001-2024. Sometimes forests are cleared, farmed for a few years, and then left to regrow as forests — a practice known as shifting cultivation — while in other cases, forests are permanently cleared, destroying their ability to act as a carbon sink. Emissions from agriculture-driven tree cover loss have risen steadily over the past two decades.
But in 2023 and 2024, a different threat took center stage: forest fires. Fires surged across the globe — from tropical rainforests in South America to boreal forests in Canada and Russia — releasing more than 4 Gt of greenhouse gases each year (including carbon locked in trees, as well as methane and nitrous oxide from burning). That’s equivalent to adding a third of China’s annual emissions into the atmosphere each year. This marks an extraordinary uptick, with fires in 2023 and 2024 releasing 2.5 times the emissions they typically do in a year.
At the same time that forest loss causes emissions, healthy and growing forests remove carbon dioxide from the atmosphere. For every hectare of tree cover lost globally between 2001 and 2024, 7 hectares remained standing. These standing forests remove carbon from the atmosphere and combat climate change in addition to myriad other benefits, like providing habitat for plants and animals, and supplying a sustainable source of timber.
Forests vary in how much they contribute to overall carbon removals:
- 66% of carbon removals since 2000 have come from “middle-aged” secondary forests. These are forests that are at least 20 years old and are regrowing after harvests, fire, agricultural conversion or other disturbances. Proportionally, these forests make up 66% of global forest extent and include everything from intensively managed temperate forests to regenerating tropical ones.
- Newly growing secondary forests younger than 20 years old make up just 2% of all forest area and provide about 6% of global annual forest carbon removals. These young secondary forests sequester carbon rapidly during early stages of regeneration following previous disturbances, due to their fast growth rates.
- Intact forest landscapes and primary tropical rainforests, covering just over one quarter (27%) of global forest area, store large amounts of carbon accumulated over decades or centuries, which is emitted when these forests are cleared, burned or otherwise disturbed. However, they generally don’t remove as much carbon as younger forests and account for only 13% of total carbon removals.
- Plantations and tree crops contribute 13% of global carbon removals despite covering only 4% of forest extent because they are able to sequester carbon rapidly as they grow. However, sustaining the long-term carbon sequestration potential of timber plantations depends on allowing enough trees to remain unharvested so they can continue to remove carbon from the atmosphere.
- Mangroves account for approximately 2% of total carbon removals while accounting for only 0.2% of global forest extent. They store large amounts of carbon in their soils over long periods and provide benefits like coastal protection and biodiversity support.
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Net Sink or Net Source? It Depends on Where and When You Look
When we add up emissions from forest loss and removals from standing and regrowing forests, we can see that at a global scale forests are still a net carbon sink, but it’s weakening. Regional patterns, however, tell a more nuanced story.
Some forest regions — including parts of China and the eastern United States — have remained relatively strong net carbon sinks. Others, like the tropical forests of Bolivia and boreal forests in Canada, have turned from net sinks into net sources.
For example, between 2016 and 2020, Bolivia’s forests oscillated between a slight net source and net sink driven largely by agricultural expansion. In 2023 and 2024, Bolivia’s forests became a decisive source, with fires contributing 60% of forest emissions. Fires burned nearly 1.5 million hectares in 2024 alone, releasing an estimated 400 million metric tons of greenhouse gases — 11 times higher than the annual average. This marks Bolivia’s largest fire year on record, pushing its forests to become a greater net carbon source than ever before. -
In Canada, forests also became a net carbon source in 2023 and 2024 due to intensifying wildfires. Canadian fires were responsible for 65% of global fire-related tree cover loss in 2023, yet accounted for 79% of global forest fire emissions. Although fire activity was lower in 2024, Canada still contributed 32% of global fire-related tree cover loss and a disproportionate 53% of global forest fire emissions.
Many of the fires in Canada burned through surface vegetation as well as deep layers of carbon-rich peat soils — which release disproportionately high levels of greenhouse gases when burned — causing “zombie fires” that can smolder underground through winter and re-emerge the following spring. An estimated 74% of forest fires in Canada in 2023 and 2024 occurred within peatlands. While fire is a natural part of forest ecosystems in Canada, the recent surge in wildfire activity is unusual and may indicate a major shift in regional fire patterns.
In contrast, forests in the eastern United States’ Appalachian region have been a robust carbon sink over the past several decades and offer a more hopeful example of how past land use and natural regeneration shape today’s forest carbon dynamics. Most of these forests were cleared for agriculture and logging by the mid-20th century, but then were abandoned and allowed to regrow naturally. Today, these recovering secondary forests account for a quarter of the U.S. net forest carbon sink despite comprising only 14% of the country’s forested area. Managed for multiple uses including timber harvesting, recreation, wildlife habitat and watershed protection, and less affected by large-scale fires, these forests highlight the long-term climate value of allowing forest ecosystems to regrow on formerly cleared land. However, factors such as forest aging, increased disturbances and climate-related stressors like drought and warming temperatures mean their future capacity to sequester carbon is becoming more uncertain. -
Shoring Up the Forest Carbon Sink: 8 Levers for Climate Action
Forests are still doing incredible work for the climate, but they may be reaching a breaking point. To keep the remaining forest carbon sink intact — and ideally expand it — we must act across multiple fronts:
- Protect what we have. Most forest carbon removals come from existing forests — not newly planted ones. The most important step we can take is to stop further loss of primary and regenerating secondary forests. This requires clear rules to protect forests, people to enforce those rules, and policy changes that make it harder to profit from cutting forests down.
- Reduce fire risk through smarter land management. Investing in proactive fire prevention like prescribed burns, fuel thinning and fire-resilient restoration — as opposed to relying solely on reactive fire suppression — is essential. Strategies must be tailored to local ecosystems: Some forests need low-intensity fire, while others must be fully protected from all burning. Combining indigenous knowledge with tools like GFW’s fire alerts can help.
- Better manage “working” forests. In forests used to provide timber and other forest products, sustainable management can reduce emissions and increase removals. Techniques such as reduced-impact logginglonger harvest rotations, and shifts to species better adapted to future climate conditions while preserving local biodiversity can help ramp up forests’ carbon sequestration abilities without shutting down economic use.
- Accelerate restoration. Restoring forests can help fight climate change, but it must be done the right way. Natural and assisted restoration of degraded forests can enhance carbon sinks. Restoration should complement, not substitute for, forest protection.
- Support the people who protect forests best. Indigenous Peoples and local communities are often the best protectors of forests, yet they receive a fraction of global climate finance. From 2001 to 2024, forests in Indigenous territories across the Amazon absorbed an amount of carbon equivalent to France’s annual fossil fuel emissions, while surrounding non-Indigenous lands were collectively a net carbon source. Redirecting funding to support locally led conservation, restoration and securing land tenure is one of the highest-impact, lowest-cost investments we can make for sustaining and growing the forest carbon sink.
- Make climate data timely and actionable. Systems fail when data is missing, delayed or ignored. Tools like GFW provide timely, open data on forest emissions and removals, but information alone isn’t enough. We have to act on it.
- Align supply chains with forest protection. Many globally traded commodities like beef, soy and palm oil continue to drive deforestation. Governments, companies and financial institutions must act together to ensure these products are truly deforestation-free — not just in the form of pledges, but in practice. At the same time, reducing overconsumption of land- and carbon-intensive goods like beef is essential. Sustainable supply chains won’t succeed without more sustainable demand.
- Reduce fossil fuel emissions. We can’t expect forests to absorb the world’s excess carbon emissions indefinitely. To ease pressure on natural systems, we must dramatically cut fossil fuel emissions. The forest carbon sink is not a fallback plan that can make up for inaction elsewhere.
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2024 was the hottest year on record, with average temperature rise exceeding 1.5 degrees C (2.7 degrees F) for the first time in recorded history. And yet without action, it may prove to be one of the most stable years of our lifetimes. Crossing the 1.5 degrees C warming threshold is a flashing red signal that climate tipping points may be closer than we thought.
Forests are a critical part of avoiding this tipping point. They’re remarkably resilient, but their biological limits are not negotiable. If we want forests to continue absorbing carbon from the atmosphere, then we need to give them the space and stability they need to function.
This means rethinking how we value them — not just as a source of lumber or land, but as a planetary life-support system. Protecting the world’s forests isn’t charity; it’s survival.
- Cover photo: Loren McIntyre/Alamy
