How relevant is climate change research for climate change policy? An empirical analysis based on Overton data

confirmed as ‘dummy’ publication dates by Euan Adie or contained many policy documents published later than the specified date (see https://help.overton.io/article/why-am-i-seeing- unknown-date-instead-of-a-publication-date). We used PostgreSQL and R [30] commands including the R package ‘tidyverse’ [31] for data analysis. We searched in the fields ‘title’, ‘translated title’, and ‘snippet’ for climate-change-related terms in the Overton snapshot. We searched for ‘climate change’ and ‘global warming’ (note that both terms were truncated on both sides and a single arbitrary character was allowed instead of the white space between the words) to cover the bulk of policy documents that are related to climate change. The search strategy is based on keyword analyses in connection with search queries of previous climate change related papers [21, 22]. We found 10,846 policy doc- uments that met the climate change search criteria out of 799,716 policy documents with any citation relation to a scientific paper or another policy document. The Overton database includes links to scientific publications via digital object identifiers (DOIs)–“scholarly” references in Overton must have a DOI. There are 8,533,973 citation rela- tions from 492,958 policy documents to 3,242,626 scientific papers. We used the SciTech Strat- egies’ in-house version of Scopus containing 52.04 million items indexed as of May 2020 and published between 1996 and 2019 as a database for scientific papers. 76.7% of these items have

a DOI. We were able to match 2,071,085 DOIs cited in Overton to Scopus papers. Thus, nearly 4.98% of Scopus items with a DOI have been cited by policy documents indexed in the Over- ton database. This is substantially higher than the 1.12% mentioned in Fang, Costas [24]. We used the journal metric CiteScore to measure the citation impact of journals [32]. It is the mean number of citations for papers published in a journal. For the current study, Cite- Score values were downloaded from https://www.scopus.com/sources.uri on November 10, 2020. The most current CiteScore values from 2019 were used for our analyses. Results Policy documents This study is based on 10,846 climate change policy documents covered in the Overton database. This corresponds to 1.36% of all policy documents in the database. Fig 1 shows the distribution of the climate change policy documents across publication years. For a better interpretation of this distribution, we also included distributions for all policy documents in the Overton database and the papers on climate change in the Scopus database. The comparison of climate change with all policy documents reveals that the climate change policy documents reached a plateau in 2015 whereas all policy documents steadily increased until 2018. Since the scientific paper distribution also shows a steadily increasing trend, it seems that the discussion of climate change in the policy area reached its maximum several years ago (at least temporarily). Policy documents can be published by various types of institutions. Based on the classifica-

tion of these institution types used in Overton, Fig 2 shows the percentage of policy documents published by think tanks, governments, and IGOs. The comparison of climate change policy documents with all policy documents in Fig 2 reveals that climate change documents were pub- lished by think tanks and IGOs at higher than expected rates given their overall share of policy documents; fewer climate change documents were published by governments than expected. This substantially lower share of climate documents issued by governments could be a reflection of their hesitance in dealing with the problem of climate change as documented in continued emissions growth [33–35] as well as the gap between long-term ambition and short- term actions [36, 37]. NGOs and IGOs might be particularly active in the field of climate change. IGOs, for example, may consider climate change as a problem of international coordi- nation in nature. PLOS ONE How relevant is climate change research for climate change policy? PLOS ONE | https://doi.org/10.1371/journal.pone.0274693 September 22, 2022 6 / 24