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Natural carbon sinks absorbed around 40 per cent of global carbon dioxide emissions from human activities in 2025, but weakening forests and oceans and inadequate financial incentives to protect them could undermine climate strategies built around their continued capacity to absorb carbon, according to a new analysis by Wood Mackenzie.
The energy and commodities research firm estimates that oceans absorbed approximately 12 GtCO2 in 2025, while forests absorbed a further 6 GtCO2. Against gross global carbon dioxide emissions of 48 GtCO2 a year from energy, agriculture, waste and land use and forestry, the natural sinks reduced net emissions to approximately 30 GtCO2.
Net CO2 emissions from human activities have nevertheless risen more than 80 per cent since 1990, highlighting the growing gap between rising emissions and the capacity of natural systems to absorb them.
The findings are from Wood Mackenzie's Nature capital: the unpriced carbon report, published in August 2026. The report argues that natural sinks remain a largely unpriced component of the global climate system even as countries increasingly rely on carbon removal and net zero strategies.
The scale of natural carbon absorption far exceeds that of engineered carbon removal technologies. Direct air capture and bioenergy with carbon capture and storage together contributed only 0.08 GtCO2 of removals in 2025.
Ocean uptake alone was more than 200,000 times greater than engineered removals during the year. The comparison highlights the continued dependence of climate strategies on natural ecosystems despite growing investment and policy attention around engineered carbon removal. Wood Mackenzie says the vast majority of CO2 removal has historically depended on natural systems.
Natural sinks, however, are under increasing pressure. Global forest area has declined by 1.5 million square kilometres since 1990, while deforestation contributes 5 to 6 GtCO2 annually. The land use sector has had near neutral net emissions since 2024, meaning it has lost its role as a net sink.
In Wood Mackenzie's base case, forest area continues to contract until 2030 before gradually recovering. Rising temperatures could reinforce the decline as higher temperatures increase the risk of fires, which in turn reduce the capacity of forests to absorb carbon. Protecting and restoring forests could provide 3 to 6 GtCO2 of mitigation annually, according to the report.
The report identifies five major Earth system tipping points with a combined potential to release more than 750 GtCO2. These include permafrost thaw, Amazon dieback, boreal forest fires, coral reef die off and disruption of Atlantic Ocean circulation.
Some of these processes are already occurring. Canada's 2023 boreal fires released 3 GtCO2, according to Wood Mackenzie, turning boreal forest from a carbon sink into an emissions source.
The consequences extend beyond the carbon balance. Coral reefs die off, for instance, would disrupt fisheries that support more than a billion people globally. The report therefore frames the condition of natural ecosystems as a factor in the reliability of climate scenarios, rather than solely as an environmental concern.
Even aggressive emissions reduction does not eliminate the need for carbon sinks and removals. Under Wood Mackenzie's net zero scenario, approximately 11 GtCO2 of annual energy sector emissions remain in 2050 even as global net emissions reach zero by that year. Under its country pledges scenario, around 14 GtCO2 of annual energy sector emissions remain by 2060, when net emissions reach zero. This means residual emissions would still need to be balanced by natural sinks and engineered carbon removals.
The report says financing gaps in the land use sector have left the natural sink capacity required to absorb residual emissions, alongside engineered removals, underdeveloped.
Wood Mackenzie estimates that carbon prices in most compliance markets range from $5 to $90 per tCO2. The report says these prices do not reflect the cost of degradation of natural sinks or provide sufficient incentives for investment in their protection. It identifies this as a structural gap in current climate policy. Natural sinks are effectively treated as free infrastructure, while carbon emissions are assigned a price.
The report argues that stronger carbon pricing, increased finance for nature and policy action will be required to prevent further weakening of natural absorption capacity.
The 2026 to 2035 period will be particularly important, with Wood Mackenzie's scenario analysis showing that sink trajectories diverge significantly depending on the action taken during this period.
“Unlike the energy transition, which can accelerate in later years, ecosystem collapse is permanent on human timescales. Each decade of inaction removes future optionality,” said Roshna Nazar, senior analyst, Energy Transition Scenarios and Technologies, Wood Mackenzie.
“The due diligence gap is straightforward: any net zero strategy that assumes stable natural absorption without assessing sink health is building on unverified foundations,” Nazar said. “Early movers in verified nature based solutions and sink linked carbon instruments will capture value as demand scales and regulation tightens.”
Wood Mackenzie's Lens Energy Transition Scenarios research models the full CO2 balance under four scenarios through 2060: base case, country pledges, net zero and delayed transition.
The report says natural sinks are not adequately valued in most energy or climate models. As efforts to address this gap develop, carbon prices, offset methodologies and national climate plans could face material revisions. It also warns that regions with weak enforcement could face abrupt policy tightening as losses in natural carbon sinks become more visible, creating sudden compliance burdens for exposed assets.