Scientific literature on carbon dioxide removal revealed as much larger through AI-enhanced systematic mapping

Abstract

Carbon dioxide removal plays an important role in any strategy to limit global warming to well below 2 °C. Keeping abreast with the scientific evidence using rigorous evidence synthesis methods is an important prerequisite for sustainably scaling these methods. Here, we use artificial intelligence to provide a comprehensive systematic map of carbon dioxide removal research. We find a total of 28,976 studies on carbon dioxide removal-3-4 times more than previously suggested. Growth in research is faster than for the field of climate change research as a whole, but very concentrated in specific areas-such as biochar, certain research methods like lab and field experiments, and particular regions like China. Patterns of carbon dioxide removal research contrast with trends in patenting and deployment, highlighting the differing development stages of these technologies. As carbon dioxide removal gains importance for the Paris climate goals, our systematic map can support rigorous evidence synthesis for the IPCC and other assessments.

Fig. 1. Overview of the data retrieval for this study.

Squares symbolise documents, a coloured square a document with labels, either assigned by hand (solid colour) or automatically (faded colour). Red documents are excluded, blue ones included. Step 1: 70,000 documents were retrieved from databases using search queries. Step 2: Of these about 6000 documents are sorted (=coded) by hand into being on CDR (relevant, blue squares) or being not on CDR (irrelevant, red squares). Documents on CDR were additionally described with CDR options, see Fig. 2, and other categories. Steps 3 and 4: The relevance labels and additional categories were used to train machine learning classifiers. Step 5: The trained classifiers were used to extend all labels to the unseen ~64,000 documents. Detailed information on methods can be found in the “Method” Section and the Supplementary Methods 3 and 4.

Fig. 2. Schematic overview of the coding guidelines used for inclusion in the systematic map.

The definitions of each carbon dioxide removal (CDR) option shown in this figure served as the baseline for inclusion. Additional coding guidelines are provided in the Supplementary Methods.

Fig. 3. Time development of the scientific literature on CDR in Web of Science and Scopus.

a Total number of publications per year between 1990 and 2022. Additionally, we note the number of publications released during each Assessment Report (AR) cycle of the Intergovernmental Panel on Climate Change, the latest AR6 considered publications until 2021. b Share of CDR option covered in scientific publications. Multiple options per publication are possible. A more complete list of all counts per option is published in the Supplementary Fig. 1. c Annual growth rate of the scientific literature on CDR, climate change and individual options. Growth rate is only calculated if there were more than 50 publications in total available. Colorblind-friendly versions of the middle and lower panel can be found in the Supplementary Figs. 2 and 3. Source data is provided as a Source Data file.

Fig. 4. China dominates the scientific literature on CDR.

a Number of studies per country based on first author affiliation. The three highest study counts are added. b We sort the origin of the study into the world regions. For each world region, we compare the percentage difference of the investigated CDR options against all others from the complete dataset. Displayed are only the three highest and the three lowest differences. c Location-based research derived from locations mentioned in title and abstract. Displayed is the share of location-based research in all scientific literature per CDR option. A colorblind-friendly version of panel b can be found in the Supplementary Fig. 4. Source data is provided as a Source Data file.

Fig. 5. Most studies focus on investigating the CDR option from a technical perspective, where the technology or ecosystem management method itself is investigated.

a The number of studies which report on each of the CDR options. One study can report on multiple CDR options. b For each CDR option the share of research fields the studies were published in. This is based on meta-data from the Web of Science and follows the OECD Category scheme. c For each CDR option the share of scientific method used in the studies as identified by our classifier. One study can use multiple methods, see Supplementary Table 3. Source data is provided as a Source Data file.

Fig. 6. Comparison of all literature on CDR with CDR papers cited by the 6th assessment of the IPCC (reports of all three working groups).

Reading guide for colorblind people: The categories follow the order listed in the legend, beginning from the top of each circle and proceeding counterclockwise. Source data is provided as a Source Data file.

Fig. 7. Share of CDR options for current deployment of CDR, patenting activity, scientific literature, invested capital and considerations in the scenarios assessed in the recent IPCC report.

Data was taken from ref. . Source data is provided as a Source Data file.