Relying on large-scale Carbon Dioxide Removal risks damaging the Biosphere

Sand art of trees
The recent news that global average temperature has surpassed 1.5°C underscores the urgent need for swift action in reducing greenhouse gas emissions, rather than placing undue faith in risky technologies.

Governments and companies globally are becoming increasingly reliant on carbon dioxide removal (CDR) technology to meet Net Zero targets while avoiding the need to make deep (and often unpopular) emission cuts.  However, a recent analysis published in the journal Science has highlighted crucial social and ecological constraints on the sustainable removal of carbon dioxide from the atmosphere, with significant implications for Net Zero strategies.  

The authors illuminate substantial risks associated with over-reliance on Carbon Dioxide Removal (CDR), not solely around technical and economic challenges, but also concerning the vast scale envisioned in certain 1.5°C pathways produced by the Intergovernmental Panel on Climate Change (IPCC). Such reliance could profoundly jeopardise the health of the biosphere. In particular, the extensive land requirements for biomass production, predominantly monocultures with minimal climate resilience, pose substantial threats to biodiversity. This jeopardises the resilience of the biosphere and the attainment of targets outlined in the Global Biodiversity Framework, while also compromising food and water security and encroaching upon human rights.

The most common approach to CDR at present is tree planting, but future options are expected to include biomass energy with carbon capture and storage (BECCS), or novel techniques such as spreading ground-up rock on farmland (enhanced weathering) and direct air carbon capture and storage (DACCS).  

The study looked at three groups of land-based CDR options: BECCS, tree-planting (including monocultures), and ‘nature-based’ options including ecosystem restoration and agroforestry with limited land-use change. They found that while the IPCC assumed BECCS could remove an average of 5.9 billion tonnes of CO2 per year, only 1.2 billion tonnes is available at ‘low risk’ of adverse social and ecological impacts, or 2.8 billion tonnes at medium risk. Beyond that, the risks of adverse impacts are high or very high.

These estimates are optimistic, as they assume 70% of the carbon produced via BECCS can be captured and stored safely – if that figure fell to 50%, the amounts available at low risk would be just 0.7 billion tonnes. Thresholds would fall even further unless measures are put in place to avoid serious risks such as biomass cultivation leading to deforestation, and also to fix accounting loopholes that ignore emissions arising from biomass harvest and processing.

For tree-planting, the authors estimate that 3.8 billion tonnes of CO2 can be removed at low or medium cost, close to the IPCC estimate of 3.9 billion tonnes. Risks are lowest (and feasibility highest) for nature-based CDR such as forest restoration using a diverse mix of species, where 5.1 billion tonnes of CO2 can be removed per year at low or medium risk.

In light of these findings, the authors conclude that the IPCC’s forthcoming seventh assessment report and the next round of Nationally Determined Contributions (NDCs) in 2025 should revise estimates of CDR potential to include social and ecological limits and be transparent about the area of land required. For example, existing NDCs will produce double the emissions consistent with a 1.5°C pathway by 2030, and then plan to use 12 million km2 for CDR by 2060 – almost the entire area of global cropland. They also recommend considering how to allocate the limited supply of sustainable CDR for the most important uses.

Most importantly, the study shows that we can adopt climate mitigation pathways that do not exceed these limits. For example, the three IPCC pathways that rapidly cut energy demand and shift to renewables only need to remove 2 or 3 billion tonnes of CO2 a year by 2050 and 3 to 6 billion in 2100, most of which could be done using low or medium-risk options.

In contrast, the IPCC’s ‘Neg’ pathway delays climate action, leading to a large overshoot of emissions. It therefore relies on CDR to remove 5 billion tonnes of CO2 a year by 2050, increasing to 15 billion tonnes by 2100 – most of which would be at high or very high risk of adverse impacts. For example, this would require 13 million square kilometres of land by 2100, 40% larger than the area of the US.

These findings emphasise why nature-based solutions (NbS) to climate change must be implemented with integrity. High-quality nature-based solutions not only reduce or eliminate the risk of adverse social and environmental impacts, but also deliver multiple benefits beyond carbon removal, helping to address the impacts of climate change such as floods, droughts and heatwaves as well as bringing benefits for human health and biodiversity. 

Following the four NbS guidelines and the more detailed IUCN Global Standard on NbS will ensure that NbS do not delay urgent action to phase out fossil fuels; that they are implemented in partnership with local communities, respecting human rights; and that they deliver benefits for biodiversity. Similar social and ecological protections also need to be applied to BECCS.

Other CDR methods such as DACCS, enhanced weathering or ocean-based CDR, also have risks that have not yet been fully assessed. The authors of this paper express concern that this reliance on poorly understood technologies is fuelling a false sense of security, deterring stronger action to cut emissions now.

‘Governments and industries are relying on future large-scale, land-based carbon dioxide (CO2) removal (CDR) to avoid making necessary steep greenhouse gas (GHG) emission cuts today. Not only does this risk locking us into a high overshoot above 1.5°C, but it will also increase biodiversity loss, imperiling the KunmingMontreal Global Biodiversity Framework (KMGBF) goals. Such CDR deployments also pose major economic, technological, and social feasibility challenges; threaten food security and human rights; and risk overstepping multiple planetary boundaries, with potentially irreversible consequences’ – Deprez et al., in Science.

While CDR is widely regarded as a key solution to combat climate change, evidence brought together in this new paper strongly indicates that large-scale deployment of technologies such as BECCS poses significant risks to our environment and to food and water security.

The recent news that global average temperature has surpassed 1.5°C underscores the urgent need for swift action in reducing greenhouse gas emissions, rather than placing undue faith in  risky technologies. To address both climate change and biodiversity loss, we must prioritise immediate and substantial reductions in fossil fuel usage, eliminate harmful subsidies that damage the biosphere, and scale up investments in robust, biodiversity-based, community-led nature-based solutions. Future studies, including the next generation of IPCC pathways, urgently need to explore more innovative approaches that reduce wasteful consumption patterns, and alternative economic models that prioritise sustainability over unchecked expansion. It is only through such comprehensive and transformative approaches that we can safeguard the health of our planet for generations to come.

Read the paper here.