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Why does burning forests release carbon dioxide?

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Edge of a dense forest in Romania where clear cutting has removed most trees, leaving a bare, brown slope beside standing green trees. — Deforestation A section of clear-cut forest in Romania.

Forests play a critical role in the carbon cycle by acting as natural carbon sinks. As trees grow, they sequester carbon from the atmosphere, incorporating it into their wood and other biomass through the process of photosynthesis.12

When forests are burned, this stored carbon is released back into the atmosphere as carbon dioxide. This process is significant for two reasons:12

Direct Emission: The combustion of the biomass immediately returns the sequestered carbon to the atmosphere as a greenhouse gas, which contributes to global warming.12
Loss of Future Sequestration: Once the trees are destroyed, they are no longer present to continue absorbing carbon dioxide from the atmosphere, further exacerbating the accumulation of greenhouse gases.12

While natural decomposition also releases carbon over time, the rapid burning of forests—often associated with deforestation or slash-and-burn agriculture—accelerates this release, turning a long-term carbon repository into a source of atmospheric pollution.324