A review of research on carbon dioxide removal reveals a lack of evidence on its costs, impacts and benefits in Africa and South America.

A review of research on carbon dioxide removal (CDR), carried out by a team from the Grantham Institute – Climate Change and the Environment at Imperial College London, the Humboldt University of Berlin and the Mercator Research Institute on Global Commons and Climate Change, reveals a lack of evidence on its impacts and benefits in Africa and South America, where many CDR schemes are planned.

CDR covers a broad swathe of methods to remove carbon dioxide (CO2) from the atmosphere, including reforestation, the manipulation of farmland to improve the carbon absorption of soils, and more technological techniques like carbon capture, utilisation and storage (CCUS).

The Intergovernmental Panel on Climate Change says CDR is required to achieve global and national targets on greenhouse gas reductions, and CDR schemes are a key component of models used by policymakers to make decisions about climate change mitigation.

This study shows, however, that while research on CDR and its impacts has risen dramatically in recent years, the vast majority has so far focused on Europe and Asia, or on the global picture.

“The underrepresentation of Africa and South America in the scientific literature is critical since these regions are considered essential for CDR deployment. The few studies that do exist mostly highlight negative aspects,” says lead author Ruben Prütz, a Visiting Researcher at the Grantham Institute.

Understanding the impacts

The work, which used machine learning to select relevant research and produce an inventory of nearly 400 CDR co-benefits, challenges, and limits, found a similar focus on negative effects across the literature.

These negative side effects included impacts on biodiversity, soil and land use. In addition to specific impacts, there is uncertainty concerning the effectiveness and scalability of some CDR methods.

Some research has highlighted that CO2 removal could delay climate action and may shift the burden of mitigation to other countries. Previous research also suggests CO2 removal may be inconsistent with international law.

However, the authors note that this emphasis on the negative effects may only reflect the current evidence and not CDR’s real-world costs and benefits.

The authors did also find positive effects of CDR. Evidence exists showing positive impacts on soil (through increases in key nutrients such as nitrogen, phosphorus, and potassium); yield increases for various crops such as maize, soybeans, and tomatoes; and increases in biodiversity.

The paper emphasises that these are highly dependent on the context and which CDR method is deployed. For instance, there may be big differences between sustainable forest management versus planting thousands of acres of non-native palm trees where there once was rainforest.

The authors argue this underlines the need for further evidence to better understand the size of the impacts of CDR, its side effects, the contexts, and the modes of implementation for affected countries.

Co-author and Director of Research at the Grantham Institute, Professor Joeri Rogelj, said: “Our study describes the current literature, which is vast but also shows gaps. Not every removal measure is studied in equal depth and for all countries. Looking at our inventory allows us to direct research attention to start filling these gaps.”