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The Carbon Sink: Why It’s Not as Full as We Thought

Forests once seemed invincible in absorbing carbon—but fires, deforestation, and climate change reveal limits and urge urgent action to protect our climate sinks.

By Medha deb

Created on Sep 27, 2025

Forests once seemed invincible in absorbing carbon—but fires, deforestation, and climate change reveal limits and urge urgent action to protect our climate sinks.

For decades, forests have acted as the planet’s lungs—removing carbon dioxide (CO₂) from the atmosphere and helping slow the rate of climate change. Researchers, policymakers, and climate advocates have long hoped that forests and other natural ecosystems would buy us time as humans work to curb emissions. But recent data and scientific analysis show the limitations of this vital service as climate pressures and human activities escalate. The world’s carbon sink is not bottomless. In fact, it’s running out of room.

Understanding Carbon Sinks: Nature’s Climate Service

Carbon sinks are natural systems that absorb more carbon than they release. The major terrestrial sinks are forests, grasslands, and soils. Oceans are also key players, but terrestrial carbon sinks absorb roughly 30% of the carbon dioxide generated by human activity each year. Forests, in particular, have long been presumed to be reliable, predictable absorbers of atmospheric CO₂.

Forests take in CO₂ through photosynthesis, storing carbon in trunks, leaves, and roots.
Soils beneath forests also lock up significant quantities of organic carbon.
Globally, forests and vegetation remove about 30% of anthropogenic carbon emissions each year.

This natural climate regulation has allowed scientists, economists, and activists to lean on forests as a climate buffer—one humanity desperately needs as carbon emissions from burning fossil fuels remain high. But is this cushion as dependable as once hoped?

Shifting Realities: The Forest Carbon Sink Is Shrinking

Although forests still play their important role, their capacity as carbon sinks has changed significantly in recent years. According to recent analysis, 2023 marked the lowest forest carbon sink recorded in at least two decades, with forests absorbing only a quarter of the carbon dioxide they do in a typical year. This dramatic reduction is a warning sign that the system’s resilience is being eroded.

Year	Average CO₂ Absorbed by Forests	Key Factors Affecting Sink
Pre-2020s	~3.5 billion metric tons/year	Deforestation, moderate wildfires
2023-2024	~1/4 usual absorption	Record-breaking fires, persistent deforestation

The effects of this decline are not abstract: if forests switch from being net absorbers (sinks) to net emitters (sources) of carbon, global efforts to combat climate change could be critically undermined.

Why Is the Carbon Sink Diminishing?

The shrinking capacity of forests to act as carbon sinks is primarily driven by two intertwined phenomena: persistent deforestation and a surge in extreme wildfires. Here’s how each contributes:

1. Deforestation: Clearing the Vault

Over 80% of forest-related emissions originate from human-driven tree clearance, whether for agriculture, timber, infrastructure, or minerals.
Agriculture is the main driver, causing over half of all tree cover loss emissions between 2001–2024.
Permanent clearing eliminates a forest’s ability to absorb carbon in the future.

When forests are felled, not only do they stop sequestering carbon, but the carbon stored for centuries in trunks and soils is released back into the atmosphere. Some cleared lands—in the process known as shifting cultivation—are later allowed to regrow, but this rarely compensates for the losses from permanent deforestation, especially for primary (old-growth) forests.

2. Wildfires: Burning Through Our Buffer

Over the last two years, global wildfires—exacerbated by drought and rising temperatures—have torched millions of acres of boreal and tropical forests.
Forest fires in 2023 and 2024 released over 4 gigatonnes of greenhouse gases each year—2.5 times higher than typical years.
This equates to adding a third of China’s annual emissions into the atmosphere annually.

Wildfires not only release the carbon stored in wood and soil, but also reduce the amount of forest available to act as a future carbon sink. This compounding effect undermines forests’ long-term carbon storage potential. Rising global temperatures and more frequent droughts—a byproduct of climate change—contribute to larger, more severe, and more frequent fires, creating a dangerous feedback loop.

The Edge Effect: Underestimating Urban and Fragmented Forests

Forests are not uniform. They are fragmented into patches by roads, development, and agriculture. Edges—the outermost areas of these fragments—behave differently than interior forest. Recent research reveals that urban and fragmented forests absorb more carbon than previously measured. Edge trees, which receive more sunlight and nutrients, often grow faster and pull in more carbon than their interior counterparts.

Edge trees in temperate urban forests often grow faster than those in deep forest, thanks to increased sunlight and nutrient runoff from human environments.
Urban soil can also store unexpectedly high amounts of carbon.
However, edges are more susceptible to disturbance, which can cause stored carbon to be released quickly.

This complicates our models: while these edges currently seem to punch above their weight in soaking up carbon, they may be short-lived. As forests become more fragmented, they become more vulnerable to heat, drought, and invasive species, and their long-term ability to serve as carbon sinks may dwindle.

Regional Differences: Boreal vs. Tropical Forests

Global analyses show that the fate of the carbon sink varies by region and forest type:

Boreal forests—spanning Alaska, Canada, and Russia—have lost 36% of their carbon sink capacity. Increased wildfire, insect infestation, and soil warming are major culprits.
Tropical forests have seen a 31% decrease due to deforestation, though regrowth in abandoned agricultural lands has offered partial compensation.
Elsewhere, some forests continue to absorb carbon, but the balance is shifting everywhere. Deforestation and disturbances mean few regions can be considered stable or expanding carbon sinks.

While forests overall continue to remove several billion tons of CO₂ annually, the rate is unstable and increasingly at risk.

Soil: An Overlooked Carbon Sink

Often unappreciated, soils—including urban soils—store massive amounts of carbon, sometimes more than the vegetation above. Changes in land use, warming, and erosion threaten this store.

Soil carbon is vulnerable to disturbances like plowing, construction, or removal of aboveground vegetation.
Urban soil in particular may hold greater carbon stocks than previously estimated, especially beneath greenspaces and forest patches.

Properly managing soils—by minimizing disturbance and maintaining ground cover—can protect this vital asset against further carbon loss.

Perils of Losing the Forest Carbon Sink

Losing forests as a carbon sink would have profound and possibly catastrophic effects:

Accelerated climate change and a spike in average global temperatures.
More extreme weather events—heatwaves, droughts, and storms.
Disrupted rainfall patterns, impacting water supply for people, agriculture, and wildlife.
Reduced food security and greater risk of famine in vulnerable regions.

Forests provide a climate service at virtually no economic cost, and their loss would force societies to look elsewhere—likely at much higher expense—for climate mitigation.

Can Technology Compensate for the Loss?

Some propose that we can offset declining forest sinks with technology—specifically “direct air capture” using giant fans to pull CO₂ from the air. While this technology is advancing, it is still expensive and energy-intensive, capturing a mere fraction of the carbon processed by natural systems each year. By comparison, forests provide their sink service for free, at far larger scales.

Forests remove far more CO₂ than all current technological solutions combined.
Technological capture costs millions per year per facility, while preserving and restoring forests is more effective and cost-efficient.

What Should We Do? Four Essential Strategies

To strengthen the world’s climate buffer and prevent further loss of natural carbon sinks, these four actions are crucial:

Protect Existing Forests: Most carbon removals come from unbroken forests. Protect primary and regenerating forests with strict policies and robust enforcement mechanisms.
Reduce Fire Risk with Smarter Land Management: Invest in proactive strategies like prescribed burns and fuel-thinning where appropriate. Tailor fire prevention to each ecosystem—some forests need fire, others need fire exclusion.
Manage Working Forests Sustainably: Implement reduced-impact logging, extend harvest rotations, promote species diversity, and use forest products wisely to increase carbon drawdown while supporting local economies.
Accelerate Restoration the Right Way: Restore degraded forests through both natural regrowth and assisted planting. Restoration should enhance—not replace—protection efforts.

Additionally, leveraging Indigenous knowledge and combining it with data from monitoring tools like Global Forest Watch can improve both protection and restoration outcomes.

Frequently Asked Questions (FAQs)

Q: Why can’t newly planted forests make up for lost old-growth forests?

A: Newly planted forests take decades—or centuries—to store equivalent amounts of carbon found in old-growth forests. Protecting existing forests is far more effective for immediate carbon sequestration.

Q: Doesn’t regrowing farmland balance out emissions from deforestation?

A: While regrowth helps, it rarely matches the carbon lost through destruction of older forests, especially when regrowth is patchy or on degraded soils.

Q: Can we rely on technology to replace forests as carbon sinks?

A: Not in the near term. Current carbon capture technology is expensive, energy-intensive, and still captures far less carbon than natural forests.

Q: How does fire management differ by region?

A: Some forests—like many North American ecosystems—require low-intensity fire for health; others (such as rainforests) are highly sensitive and must be protected from all burning. Indigenous fire management and local knowledge are vital.

Q: What can individuals do to help protect the forest carbon sink?

A: Support forest conservation organizations, reduce your carbon footprint, advocate for robust climate and forest protection policies, and make sustainable choices about wood and agricultural products.

Conclusion: The Path Forward

Nature’s carbon sinks—especially forests—are not limitless. As fires intensify and deforestation persists, the stability of our climate buffer is in question. Protecting, restoring, and better managing the world’s forests is an urgent priority for all who care about the planet’s climate, ecosystems, and future generations. The carbon sink is not full; it is closer to half-empty—and still shrinking. The time for action is now.

References

Author

medha deb

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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