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New Study Highlights Limitations of Natural Carbon Sinks in Achieving Net Zero

A recent publication from the University of Oxford’s Department of Physics, released on November 18 in Nature, unveils critical insights regarding the efficacy of relying on natural carbon sinks, such as forests and oceans, to mitigate ongoing carbon dioxide emissions from fossil fuels. This international research team articulates that such reliance will not suffice to avert the progression of global warming.

The concept of net zero, which emerged over 15 years ago, explicitly excludes natural carbon sinks when calculating human-induced carbon emissions. While these ecosystems play an essential role in moderating present-day emissions and gradually reducing the concentration of atmospheric CO2 post-net zero, there is a growing trend among governments and corporations to leverage these natural solutions as offsets for fossil fuel emissions. This shift undermines necessary reductions in fossil fuel consumption and stalls development of permanent carbon disposal methodologies. Current emissions accounting frameworks create a misleading equivalence between fossil fuel emissions and the subsequent CO2 absorption by natural sinks, leading to scenarios where a nation may appear to have reached ‘net zero’ while still contributing to greenhouse gas accumulation.

The authors of the study urge policymakers and industry leaders to be transparent about their reliance on natural carbon sinks in achieving climate objectives, emphasizing the importance of recognizing Geological Net Zero.

Geological Net Zero entails maintaining a balance between carbon emissions and storage in geological formations, mandating that every tonne of CO2 emitted due to continued fossil fuel use is matched with a corresponding tonne that is securely stored. As permanent geological CO2 storage presents both financial and logistical challenges, reaching this goal will necessitate a significant decrease in fossil fuel usage.

It is crucial, the authors argue, to protect and sustain natural carbon sinks; however, this cannot replace the imperative of reducing fossil fuel consumption. Historical emissions shape a nation’s or company’s responsibility for supporting natural sinks. For instance, the UK, with substantial past emissions but few natural sinks, implicitly obligates other nations to maintain these ecosystems long after it achieves net zero emissions—a dynamic currently overlooked in international climate negotiations.

Professor Myles Allen from the University of Oxford encapsulates the study’s message: “Our historical reliance on forests and oceans to absorb past emissions does not justify the expectation that these natural systems can also offset future emissions. Moving forward, by mid-century, any carbon released from fossil fuels must be returned to the Earth through permanent storage. That’s the essence of Geological Net Zero.”

Dr. Glen Peters of the CICERO Center for International Climate Research, a co-author of the study, highlights a crucial flaw in current reporting practices: “Countries track both emissions and removals, but incorporating all removals into climate targets is likely to perpetuate warming. Natural carbon sinks currently capture approximately half of annual emissions but should not be conflated with the fossil fuel emissions driving climate change. Simply redefining terms will not halt the rise in global temperatures.”

Co-author Professor Kirsten Zickfeld at Simon Fraser University notes a widespread misconception regarding carbon removal: “It is inaccurately assumed that removing carbon from the atmosphere can effectively counteract fossil fuel combustion. This is not the case. Offset measures will fail to be effective if they rely on actions already counted as part of the natural carbon cycle and do not involve permanent storage. Greater transparency in national greenhouse gas reporting is essential; without it, offsets might exacerbate the climate crisis rather than mitigating it.”

Professor Jo House of the University of Bristol adds to the discussion, stating: “Land resources are already constrained as they serve multiple essential functions, including food production, biodiversity preservation, and water management. They cannot feasibly offset the entirety of fossil emissions, especially as pressures like population growth and ecological disturbances escalate. Awarding carbon credits for processes that occur independently compromises the integrity of offset systems. While it’s urgent to protect natural carbon sinks, we must seek more scientifically sound and just approaches beyond current carbon offset markets.”

* The 2009 ‘Net Zero Papers’, foundational to this current research, included contributions from Solomon et al, Meinshausen et al, Allen et al, Matthews et al, Zickfeld et al, and Gregory et al. Most of the lead authors and several co-authors from those papers collaborated on this analysis, supplemented by other leading scientists in the field.

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