A recent paper, published in Science, assesses the sustainability risks of land-based CO₂ removal techniques, such as bioenergy with carbon capture and storage (BECCS), afforestation and reforestation (A/R), and nature-based CO₂ removal.

In order to address the climate crisis, we need “deep, rapid, and sustained reductions in GHG emissions, including steep reduction in fossil fuel production and use” the authors write.

They acknowledge that some CO₂ removal (CDR) will be needed in coming decades, because of hard-to-abate residual emissions, and in order to reverse temperature overshoot above 1.5°C.

“A crucial question,” they write, “is how much CDR can be deployed sustainably.”

The most recent Intergovernmental Panel on Climate Change Working Group III report estimates that BECCS and A/R could remove 11.3 and 10 gigatonnes of CO₂ per year respectively.

The authors point out the problem with these numbers:

Together, this could require converting up to 29 million km² of land – over three times the area of the United States – to bioenergy crops or trees, and potentially push over 300 million people into food insecurity.

Alexandra Deprez of the Institute for Sustainable Development and International Relations is the lead author of the paper.

She explains that one of the conclusions of the research is that, “sustainability issues such as biosphere integrity, freshwater use, and food security should be guiding limits to CDR deployment rather than the currently assessed technical and economic potentials”.

Four of the authors of the paper, Paul Leadley, of the Université Paris-Saclay, Phillip Williamson, of the University of East Anglia, Felix Creutzig, of the Mercator Research Institute on Global Commons and Climate Change, and Alexandra Deprez, wrote a Guest Post for CarbonBrief based on the findings of their paper.

In it, they write that,

The large amounts of land-based CDR in many of the pathways assessed by the IPCC come with significant implications in terms of sustainability, with the potential for serious impacts on human livelihoods and food security.

Yet the IPCC report does not comprehensively assess the environmental feasibility of the scenarios, nor their associated sustainability risks. Nor does it put a figure on the scale of CDR that could be deployed without triggering major impacts.

In the paper, the authors write,

Accounting for biodiversity losses and other land-use impacts, we find that high risk levels for BECCS and “nature-based” CDR start well below the IPCC’s mean technical potential, and the A/R threshold from medium to high risk is at the level of IPCC mean technical potential.

And Deprez explains that “high sustainability risk sets in at 1.3 GtCO₂/yr for BECCS and 3.8 GtCO₂/yr for A/R,” which she illustrates with this figure adapted from the paper:

The figure shows that “sustainability risks start well below the technical mitigation potential” the authors write in the CarbonBrief piece.

In a press statement, Leadley states that,

“The levels of carbon dioxide removal that are considered to be feasible at reasonable cost by the IPCC create high risks for agriculture, livelihoods and the environment. That’s because there isn’t enough land on our planet for huge amounts of carbon dioxide removal – something else has to give. Biodiversity, freshwater use, and food security should be the issues that guide limits to carbon dioxide removal rather than current estimates of technical and economic potentials.”

The authors write that,

The relatively low cost of land-based CDR and rapid initial deployment – especially A/R – explains why they are overwhelmingly emphasized in countries’ climate plans and IPCC scenarios for future action.

In an interview with The Times last year, Kate Dooley, a research fellow at Melbourne University’s Climate and Energy College and one of the co-authors of the recent Science report, put it more bluntly.

She told The Times that companies “tend to just come out with this large-scale tree-planting thing because that’s where you get the numbers very quickly and easily added up to how much fossil fuel you can offset”.

In a press statement about the recent paper in Science, Dooley says that,

“Carbon dioxide removal into land and forests cannot legitimately be used to offset continuing fossil fuel emissions. Government climate plans should set separate, transparent targets for emission reductions and removals, which limit reliance on the latter, and meet climate and biodiversity commitments through restoring and maintaining natural ecosystems.”

The paper ends with three recommendations:

First, set high integrity standards and regulations for CDR providers and purchasers, and across carbon markets and other sources of finance, to limit CDR use for counterbalancing truly residual emissions – not offsetting current fossil fuel emissions.

Second, call on countries in their 2025 NDC [Nationally Determined Contributions] renewal, net-zero targets, and domestic policy to not just set separate emission reduction and CDR targets but also maximize emissions cuts; minimize CDR while detailing what it is used for; and provide transparency of, and strive to limit, land-based CDR footprints.

Third, harmonize climate and biodiversity governance by deploying clear bio-energy safeguards; developing a political package to finance the protection of existing forests and ecosystems (and their carbon stocks); and prioritizing the most sustainable CDR (e.g., restoration-based CDR versus monoculture afforestation). Land-based CDR in NDCs should be coherent with states’ biodiversity conservation plans under the KMGBF [Kunming Montreal Global Biodiversity Framework]. A “CDR tracker” that scrutinizes the social and environmental impacts of current and planned CDR by states and non-state actors, and their end use, would greatly contribute to accountability and integrity. Unpacking and questioning CDR assumptions is key for getting closer to – rather than further away from – successfully addressing the intertwined climate and biodiversity crises.

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