An international team of researchers, who have been working on the science of net zero for over 15 years, has found that depending on ‘natural carbon sinks’ such as forests and oceans to counterbalance ongoing CO2 emissions from fossil fuels will not effectively halt global warming. The definition of net human-induced CO2 emissions, established years ago, does not account for these natural carbon sinks. However, governments and businesses are increasingly using them to offset emissions instead of reducing fossil fuel consumption or developing durable CO2 storage methods. Current emissions accounting rules create a misleading equivalence between emissions from fossil fuels and the CO2 absorbed by natural carbon sinks, allowing a country to claim they have reached ‘net zero’ while still contributing to global warming.
A recent study from the University of Oxford’s Department of Physics, published today (18 November) in Nature, shows that relying on ‘natural carbon sinks’ like forests and oceans to compensate for ongoing CO2 emissions from fossil fuels will not effectively combat global warming.
The concept of net zero, developed over 15 years ago,* does not consider these natural carbon sinks as part of net human-induced CO2 emissions.
These natural sinks are crucial for mitigating the effects of current emissions and for reducing atmospheric CO2 levels after the net zero target is reached, helping to stabilize global temperatures. Nonetheless, governments and businesses are focusing more on these sinks for offsetting emissions instead of cutting back on fossil fuels or finding more sustainable CO2 disposal solutions. The rules for emissions accounting reinforce this misalignment by making it possible to equate fossil fuel emissions with CO2 absorption from natural sinks, allowing countries to claim they’ve achieved ‘net zero’ while still contributing to climate change.
The authors urge governments and corporations to clarify the extent to which they depend on natural carbon sinks to achieve their climate targets and to recognize the necessity of Geological Net Zero.
Geological Net Zero refers to achieving a balance between the carbon flowing into and out of the Earth, ensuring that for every tonne of CO2 released through continued fossil fuel use, an equivalent tonne is committed to geological storage. Given the financial and practical hurdles in establishing permanent geological CO2 storage, reaching Geological Net Zero will necessitate a significant decrease in fossil fuel consumption.
The authors emphasize the critical need to protect and sustain natural carbon sinks, while acknowledging that this cannot compensate for continued fossil fuel use. The total past CO2 emissions a country or company has generated influence their obligation to maintain natural carbon sinks internationally. For example, the UK, which has high historical emissions but limited natural sinks, has essentially obligated other nations to preserve natural sinks for many years after the UK reaches net zero emissions. Unfortunately, this issue is not currently being addressed in climate negotiations.
Professor Myles Allen, from the University of Oxford’s Department of Physics and the study’s lead author, summarizes: “We are already depending on forests and oceans to absorb our previous emissions, most of which came from burning fossil fuels. We cannot rely on them to mitigate future emissions too. By the mid-21st century, any carbon still released must be permanently stored. This is Geological Net Zero.”
Dr. Glen Peters from the CICERO Center for International Climate Research in Oslo, Norway, a co-author of the study, states, “Countries report both emissions and removals, but treating all removals as part of climate targets invites ongoing warming. Natural carbon sinks currently absorb about half of our yearly emissions, yet this essential service must be seen distinctly from the fossil emissions that are driving climate change. Merely renaming items won’t halt global warming.”
Co-author Professor Kirsten Zickfeld from Simon Fraser University in British Columbia, Canada, who contributed to another of the 2009 net zero papers, mentions, “Many believe that capturing carbon from the atmosphere to offset fossil fuel combustion is just as effective as not burning those fuels in the first place. This is a misconception. Offsetting ongoing fossil fuel usage with carbon removal won’t be effective if the removal is counted as part of the natural carbon cycle and if that carbon isn’t permanently stored. We must enhance transparency in national greenhouse gas reporting and goal-setting, or offsets will become part of the problem rather than the solution.”
Study co-author Professor Jo House from the University of Bristol in the UK insists: “Land is a limited resource; we need it for food, nature, biodiversity, recreation, water storage, and more. It simply cannot offset all fossil fuel emissions now, and this will likely worsen with challenges such as population growth, wildfires, and droughts. Granting carbon credits for natural processes that are already happening undermines faith in the entire offsetting concept. We must urgently safeguard natural carbon sinks, but there are more scientifically sound and fair ways to achieve this than relying on carbon offset markets.”
* The 2009 ‘Net Zero Papers’ included research by Solomon et al, Meinshausen et al, Allen et al, Matthews et al, Zickfeld et al, and Gregory et al. Most leading authors, along with numerous co-authors from those papers, contributed to this study, alongside other key scientists focused on this topic.
