Declining natural carbon sinks are becoming a growing concern for global climate strategies, with forests and oceans absorbing around 40% of carbon dioxide emissions from human activities in 2025. According to Wood Mackenzie’s Nature capital: the unpriced carbon report, oceans absorbed approximately 12 GtCO2 and forests another 6 GtCO2 last year. Against gross annual emissions of 48 GtCO2 from energy, agriculture, waste, land use and forestry, these natural systems brought net emissions down to about 30 GtCO2.

However, net CO2 emissions have still increased by more than 80% since 1990, while the ability of ecosystems to absorb additional carbon is coming under pressure.

Natural Sinks Still Outperform Engineered Removal

The scale of natural carbon absorption remains far beyond current engineered carbon removal. Direct air capture and bioenergy with carbon capture and storage together removed just 0.08 GtCO2 in 2025, compared with 18 GtCO2 absorbed by forests and oceans.

Ocean uptake alone was more than 200,000 times larger than engineered removals during the year. This underlines how heavily climate strategies continue to depend on functioning ecosystems, even as investment in technologies such as direct air capture increases.

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Forest Loss Is Reducing the Climate Buffer

Global forest area has fallen by 1.5 million square kilometres since 1990, while deforestation currently contributes between 5 and 6 GtCO2 annually. Wood Mackenzie says the land-use sector has been near net-neutral since 2024, effectively losing its previous role as a net carbon sink. Its base case expects forest area to continue declining through 2030 before a gradual recovery.

Higher temperatures could make the situation worse by increasing wildfire risks and reducing forest carbon absorption. Protecting and restoring forests could instead deliver 3-6 GtCO2 of mitigation each year.

The Risks Also Extend Beyond Forests

Wood Mackenzie identifies five major ecosystem tipping points, including permafrost thaw, Amazon dieback, boreal forest fires, coral reef die-off and disruption of Atlantic Ocean circulation, with a combined potential to release more than 750 GtCO2. Canada’s 2023 boreal fires alone released around 3 GtCO2 and temporarily turned affected forests from carbon sinks into emissions sources.

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Net Zero Still Depends on Carbon Removal

Even ambitious emissions cuts would leave residual emissions that need to be balanced through natural and engineered removals.

• Under Wood Mackenzie’s net zero scenario, around 11 GtCO2 of annual energy-sector emissions remain in 2050 despite global net emissions reaching zero.
• Under its country pledges scenario, about 14 GtCO2 remain annually by 2060.

This creates a financing problem.

• Carbon prices in most compliance markets currently range from $5 to $90 per tCO2, which Wood Mackenzie says does not adequately reflect the degradation of natural sinks or create sufficient incentives to protect them.

The 2026-2035 period could therefore prove decisive.

• The firm argues that stronger carbon pricing, greater finance for nature and verified nature-based solutions will be needed to preserve the carbon absorption capacity assumed by many net zero pathways.

“Unlike the energy transition, which can accelerate in later years, ecosystem collapse is permanent on human timescales,” said Roshna Nazar, senior analyst at Wood Mackenzie. The report’s broader warning is that climate strategies relying on stable natural absorption need to account for the health of the ecosystems providing it.

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