Trees store carbon, and when we cut them down, that carbon goes into the air

Trees pull carbon dioxide out of the atmosphere as they grow. They use that carbon to build wood, leaves, and roots — it stays locked inside the tree for decades or centuries. When a forest is cut down, that stored carbon is released back into the air in three ways: the wood decays or burns, the soil that held carbon loses its protective cover and oxidizes, and the land often gets used for something else that produces more emissions.

Deforestation accounts for roughly 10 to 15 percent of global greenhouse gas emissions each year, according to the United Nations Food and Agriculture Organization. That makes it one of the largest human sources of climate change, second only to burning fossil fuels for energy. The effect is when ready: a tree that took 50 years to grow releases its stored carbon within months or years of being felled.

The warming happens because carbon dioxide traps heat in the atmosphere. More carbon in the air means more heat trapped, which raises global temperatures. Forests also cool the planet in a second way — they reflect sunlight and release water vapor that cools the air around them. When trees are gone, that cooling effect disappears.

Key Takeaways

  • Living trees remove carbon dioxide from the air and store it in their wood; cutting them down releases that carbon back into the atmosphere.
  • Deforestation causes warming through three pathways: decaying wood releases carbon, exposed soil oxidizes and releases stored carbon, and cleared land often becomes pasture or cropland that produces additional emissions.
  • Forests cool the planet not only by storing carbon but also by reflecting sunlight and releasing water vapor; removing trees eliminates both effects.
  • The carbon released from deforestation stays in the atmosphere for centuries, so a forest cut today continues warming the climate for generations.
  • Tropical forests store the most carbon per acre and are being cleared fastest, making tropical deforestation the single largest driver of forest-related emissions.

How carbon gets locked inside a tree and released when it is cut

A tree grows by pulling carbon dioxide from the air through its leaves. It uses sunlight to split that carbon dioxide into carbon and oxygen. The carbon becomes part of the tree's structure — the trunk, branches, roots, and leaves are mostly made of carbon compounds. The oxygen is released back into the air. This process, called photosynthesis, continues for the entire life of the tree.

The older and larger a tree is, the more carbon it holds. A mature oak or pine can store several tons of carbon. Old-growth forests — trees that have been growing for 200 years or more — store the most carbon of any forest type. When these trees are cut, all that stored carbon must go somewhere. It cannot stay in the wood once the tree is dead.

If the wood is burned for fuel or in a fire, the carbon is released into the air when ready as carbon dioxide. If the wood is left to decay on the forest floor or in a landfill, bacteria and fungi break it down over months or years, and the carbon is released more slowly. If the wood is used to build a house or furniture, the carbon stays locked up as long as the wood lasts — sometimes for decades. But eventually, that wood too will be burned or will decay, and the carbon will be released.

Soil carbon and what happens to the ground after trees are removed

Forest soil holds as much carbon as all the trees above it combined. Dead leaves, roots, and wood fall to the forest floor and decompose slowly in the cool, moist shade. Over centuries, this creates a thick layer of carbon-rich soil. The forest canopy protects this soil from sun and wind, keeping decomposition slow and carbon locked in place.

When a forest is cleared, that protection is gone. Sunlight reaches the soil, temperatures rise, and decomposition speeds up dramatically. Bacteria in the soil break down organic matter faster, releasing carbon dioxide into the air. This process can continue for years after the trees are cut, even if the land is left alone. If the cleared land is plowed for crops or compacted for pasture, decomposition accelerates further.

In tropical regions, where soils are often thin and fragile, clearing a forest can cause erosion that washes away the remaining carbon-rich topsoil. In boreal forests of the far north, thawing permafrost — ground that stays frozen year-round — releases methane and carbon dioxide that has been trapped in ice for thousands of years. Both effects add to the warming caused by the initial tree removal.

What happens to the land after deforestation and how that drives more emissions

Deforestation rarely leaves land empty. Most cleared forest becomes pasture for cattle, cropland for soybeans or palm oil, or urban development. Each of these uses produces its own emissions. Cattle produce methane as they digest food — methane is a greenhouse gas roughly 25 times more potent than carbon dioxide over a 100-year period. Cropland requires fertilizers that release nitrous oxide, another potent greenhouse gas. Clearing for development means building roads, structures, and infrastructure that require cement and steel, both carbon-intensive to produce.

The emissions from land use after deforestation often exceed the emissions from the forest removal itself. A hectare of Amazon rainforest cleared for cattle pasture releases carbon from the trees and soil, then produces ongoing methane emissions from the cattle for decades. A hectare cleared for soybean farming releases initial carbon, then requires annual fertilizer applications and tilling that keep releasing carbon from the soil.

Some cleared land is replanted with trees, which can eventually reabsorb carbon. But a plantation of fast-growing trees is not the same as a natural forest. Plantations store less carbon per acre, support far fewer plant and animal species, and are often cleared again after 20 or 30 years for another harvest. The carbon benefit is real but much smaller than preserving an existing forest.

Why tropical forests matter most for climate change

Tropical forests — those near the equator in Africa, South America, and Southeast Asia — store more carbon per acre than any other forest type. They are also being cleared faster than other forests. The Amazon rainforest alone stores roughly 150 to 200 billion tons of carbon. If it were all cleared, that carbon would add significantly to atmospheric concentrations and accelerate warming.

Tropical forests also produce their own rainfall through a process called transpiration: trees release water vapor that condenses into clouds and falls as rain. When large areas of tropical forest are cleared, local rainfall decreases, making it harder for remaining forest to survive. This creates a feedback loop where deforestation leads to drying, which leads to more forest death, which leads to more drying. Scientists worry that the Amazon is approaching a tipping point where it could shift from rainforest to savanna, releasing vast amounts of stored carbon in the process.

Tropical deforestation is driven mainly by cattle ranching and soy farming for animal feed. These industries clear forest faster than any other use. Protecting tropical forests is therefore one of the most effective ways to reduce deforestation-related emissions.

How long the carbon from deforestation stays in the atmosphere

Carbon dioxide released from deforestation does not disappear after a few years. Once it enters the atmosphere, it stays there for centuries. About half of the carbon dioxide released today will still be in the air in 30 years. A quarter will still be there in 1,000 years. This means that a forest cut down today continues warming the climate for generations, even if new forests are planted to replace it.

The warming effect also compounds over time. As temperatures rise, permafrost thaws and releases more carbon. Warmer oceans release dissolved carbon dioxide. Forests stressed by heat and drought become more prone to fire, which releases their carbon suddenly. These feedback loops mean that the warming from deforestation today can trigger additional warming tomorrow, independent of any new emissions.

This long timescale is why preventing deforestation is more effective than trying to remove carbon from the air later. A ton of carbon kept in a standing forest is worth more than a ton of carbon removed from the atmosphere decades later, because the standing forest prevents that carbon from ever being released in the first place.

The difference between deforestation and natural forest loss

Not all forest loss is deforestation. Forests are lost to wildfires, insect outbreaks, and disease without human cutting. These natural losses do release carbon, but they differ from deforestation in one key way: natural forest loss is usually followed by regrowth. A forest burned by wildfire will eventually grow back, reabsorbing the carbon that was released. The carbon cycle continues, though the timing may be disrupted.

Deforestation, by contrast, converts forest to a different land use — pasture, cropland, or development — that prevents regrowth. The carbon is released, but the forest does not return to reabsorb it. This permanent conversion is what makes deforestation a net source of emissions, while natural forest loss is often temporary in terms of carbon storage.

Climate change itself is increasing natural forest loss by making conditions hotter and drier, which fuels larger wildfires and allows pests to survive winters they once could not. This creates a vicious cycle: deforestation warms the climate, warming increases natural forest loss, and natural forest loss releases more carbon. Breaking this cycle requires both stopping deforestation and reducing the emissions that drive climate change in the first place.

Frequently Asked Questions

Does planting new trees offset the carbon from cutting down old ones?

New trees do reabsorb carbon as they grow, but it takes decades for a young tree to store as much carbon as a mature tree. A 50-year-old forest stores far less carbon than a 200-year-old forest. Planting trees is valuable, but it does not offset cutting old-growth forest on any useful timescale for climate change. Protecting existing forests is always more effective than replanting.

What about forests that are managed for timber — do they still contribute to climate change?

Managed forests harvested on a cycle do release carbon when trees are cut, but if the land is replanted and allowed to regrow, some carbon is reabsorbed before the next harvest. The net emissions are lower than from permanent deforestation, but higher than from leaving the forest untouched. The carbon benefit depends on how long trees are allowed to grow between harvests and what happens to the harvested wood.

Can we just cut down forests and bury the wood to store the carbon?

Burying wood does prevent it from decomposing and releasing carbon, but it is expensive and requires enormous amounts of land. It is far cheaper and more practical to leave trees standing, where they continue absorbing carbon for free. Biochar — charred wood buried in soil — shows promise in research but is not yet deployed at a scale that would offset deforestation.

How much of global warming is caused by deforestation versus fossil fuels?

Fossil fuels account for roughly 75 percent of global emissions, while deforestation accounts for 10 to 15 percent. Both must be addressed to limit warming. Deforestation is significant because it is one of the few emission sources we can reduce to zero relatively quickly by straightforward stopping the cutting and protecting forests that remain.