We start by highlighting the significance of COP21 and COP26 (Fig. 1). Figure 1a shows the number of posts on Twitter from 2014 to 2021. The inset shows general online engagement with COP measured using Google Trends, revealing that Twitter engagement closely reflects wider online attention. Within our study period, COP21 and COP26 are of particular significance, with the Paris Agreement signed at COP21 and the Glasgow Climate Pact agreed at COP26. Consequently, content creation and engagement (that is, retweet count) are larger for COP21 and COP26 than in the intermediate years. Our data show the influence of local engagement (inset), where the overall Google Trends scores are presented alongside country-specific scores for France (the host of COP21) and the United Kingdom (the host of COP26). Supplementary Sections 1A and 1B show a similar analysis for YouTube and Reddit, where activity is significantly lower than on Twitter.

Fig. 1: Content creation and user retweet distributions on Twitter from COP20 to COP26.
figure 1

a, Total number of Twitter posts using the term ‘COP2x’ created each day. Inset: Google Trends (GT) popularity scores for ‘COP2x’, with country-specific scores showing the local enhancement of public engagement. b, The retweet distributions for COP21 and COP26. The total numbers of retweets are shown in the top right. Extended time periods and other COPs are shown in Supplementary Figs. 1 and 2.

Ideological polarization during COP

To assess the emergence of a broad climate-contrarian community, we now analyse the evolving nature of ideological polarization between COP20 and COP26. Polarization is most often quantified in terms of the modality of a distribution of surveyed opinions38 (the definition we choose to use here; see the discussion in the Methods), although other valid definitions exist. However, on Twitter true opinion data are unavailable, so instead we infer a synthetic opinion distribution from retweet data as a proxy (Methods). In subsequent sections, we validate this proxy method by showing how opposite ends of the ideological spectrum correspond to distinct views on climate change.

We start by assuming that the climate ideology of an individual, i, can be expressed as a single number, xi (ref. 27). Polarization then refers to the properties of the probability distribution, ({{{mathcal{P}}}}(x)), of ideological scores across a population. The ideological spectrum is extracted from the Twitter retweet network using the “latent ideology” method4,5,39. Loosely speaking, the method produces an ordering of users and influencers where accounts with similar retweet interactions are close to each other in the ordering, resulting in similar scores (Methods). We specify that the majority group map to −1 and the minority to +1. Any account with an ideology score less than (more than) zero is part of the majority (minority).

We calculate the latent ideology for COP21 and COP26 (Fig. 2), where influencers are selected as the top 300 most retweeted accounts, excluding a small number (3%) that conflate the results (Methods). Influencer demographics and labelling are discussed in Supplementary Section 1D.

Fig. 2: The ideological spectra for COP21 and COP26.
figure 2

Top, a histogram of the influencer and user ideology scores for COP21 and COP26. The ideological minority group map to +1, whereas the majority group map to −1. Bottom, the 30 most retweeted influencers and accompanying user ideology distributions. Influencers who are primarily retweeted by the ideological minority are on the right, and influencers primarily retweeted by the ideological majority are on the left. Alongside each influencer, we show the distribution of user ideologies who retweeted that influencer. For COP21, no members of the ideological minority are found among the top influencers, in contrast to COP26, where we observe ideological polarization. Note, @C4Ciaran appears in the minority but has cross-ideological appeal due to tweets referencing diesel car emissions (‘Political hypocrisy and the ideological divide’). An expanded figure with all 300 influencers is available in ref. 57. For other COPs, see Supplementary Figs. 1115. Active users with fewer than 30,000 followers indicated with @_______.

The latent ideology shows unimodal user ideology for COP21, whereas the COP26 user ideology is multimodal, as confirmed by Hartigan’s diptest (Methods): the bimodality statistic, D, increases from COP21 to COP26 (COP21: D = 0.0023; 95% confidence interval, (0.0020, 0.0026); P = 0.003; COP26: D = 0.049; 95% confidence interval, (0.048, 0.050); P < 2.2 × 10−16). Despite the special significance of COP21, similarly low polarization (that is, unimodal ideologies) is found for all COPs prior to COP26 (Extended Data Fig. 1).

For both COP21 and COP26, influencers split into majority and minority actors. The majority are largely pro-climate accounts. Focusing on the minority gives some indication of the ideological divide present in these datasets. The COP21 minority has three influencers: @BjornLomborg, @Tony__Heller and @JunkScience. These individuals are climate focused and self-identify as outside the climate mainstream: @JunkScience quotes a Nature Climate Change article referring to him as “the most influential climate science contrarian”40, @BjornLomborg references his book False Alarm: How Climate Change Panic Costs Us Trillions and @Tony__Heller links to his climate-critical blog realclimatescience.com.

For COP26, we find 56 minority influencers. Of these, 6 have a clear climate focus. The remainder include media organizations and journalists (for example, @newsmax, @nypost, @GBNEWS, @PrisonPlanet and @bennyjohnson), politicians (@SteveBakerHW and @laurenboebert) and accounts campaigning against COVID-19 restrictions (@BernieSpofforth and @JamesMelville). This last group may not have strong views on climate; however, their presence in the minority remains important given how similarities in user–content interactions are used by recommendation systems41.

Qualitatively, the increase in polarization is robust to variable influencer number, different influencer definitions, different data-collection time windows and the removal of tweets related to COVID-19 (Supplementary Figs. 37). Further analysis also suggests that bot activity and deleted content do not conflate the observed increase in polarization (Supplementary Sections 2C and 2D). Our analysis shows that around 30% of climate-sceptic accounts from 2015 are no longer active on Twitter. However, deletion rates would need to exceed 80% to explain the observed increase in polarization.

One important question is whether growing polarization is a consequence of shifting views (that is, individuals moving from a majority to a minority ideological position) or changes in minority activity (that is, users with pre-existing climate-sceptic views expressing those views more prominently on Twitter). We assess this by recomputing the ideological spectrum using an equal number of minority and majority influencers who appear in both the COP21 and COP26 datasets (Fig. 3). This shows that minority influencers from COP21 remain in the minority for COP26, and majority influencers remain in the majority; over half of the minority influencers selected using this method are climate-focused accounts. However, for the standard retweet-based COP26 minority (Fig. 2), only 11% are climate focused. This demonstrates that the promotion of climate-contrarian views is shifting away from climate-focused accounts towards a broader set of non-specialized influencers. The observed increase in polarization is probably due to users with existing minority views expressing those views more prominently on Twitter, although determining this precisely is difficult.

Fig. 3: The ideological spectra for COP21 and COP26 recomputed using equal numbers of minority and majority influencers.
figure 3

Majority (minority) influencers are listed on the left (right) of each panel. The influencers selected must appear in both the COP21 and COP26 datasets. Influencer polarization is similar between COP21 and COP26, but user polarization (that is, distribution bimodality) increases significantly. This reflects a large increase in user engagement with the ideological minority during COP26 (that is, minority influencers are attracting a disproportionately large fraction of retweets in COP26 relative to COP21). More detail is provided in Supplementary Section 1G. Active users with fewer than 30,000 followers indicated with @_______, excluding elected politicians (@RogerHelmerMEP).

The political dimension of COP26

To better understand how ideological views on climate change are associated with political leanings, we now highlight the role of elected politicians in the COP26 dataset (Methods). We do this by recomputing the latent ideology twice: first, using exclusively politicians as influencers, and second, excluding politicians, generating a two-dimensional spectrum (Fig. 4). Political engagement between COP20 and COP25 is discussed in Supplementary Section 1E; for COP21, we find only one minority politician (Roger Helmer, former UK Independence Party Member of the European Parliament).

Fig. 4: A two-dimensional representation of the latent ideology, split according to political and non-political influencers.
figure 4

Triangles label the median ideological positions of accounts affiliated with specific political parties. Circles indicate the median positions of users who tweeted a particular topic, as derived using BERTopic. In Fig. 2, the latent ideology is calculated using the top 300 most retweeted accounts. Here we calculate the latent ideology twice using (1) the top 300 most retweeted accounts affiliated with individual elected politicians (x axis; political dimension) and (2) using the top 300 most retweeted accounts excluding politicians (y axis; climate dimension). The non-political axis can be thought of as the general climate dimension, whereas the political axis can be thought of as capturing the specific political groupings of the COP discussion. Some topics are merged into a single point for visual clarity.

Marking the median positions of select Anglophone political parties shows how the majority and minority, which appear homogeneous along the climate axis, split into groups with more geographical and political nuance. In the minority, we find a large block dominated by the US Republicans and former UK Brexit / UK Independence Party politicians, alongside a smaller block corresponding to the Canadian Conservative party. Related tweet extracts include calls for a “Net Zero Referendum” (Nigel Farage), claims that COP “has absolutely zero credibility” (Lauren Boebert) and statements that “everything you’ve being [sic] told by climate alarmists is a lie” (Maxime Bernier).

In the majority, we find most other mainstream political parties. It is perhaps surprising that some parties criticized as weak on climate action appear in the majority, notably the Australian Liberals42. However, this reflects pro-climate rhetoric by Scott Morrison, which attracted majority retweets (for example, “pleased to agree a new low emissions tech partnership”) as well as criticism (“#ScottyFromMarketing”).

One apparent oddity is that left-leaning political groups (for example, UK Labour and the Greens) appear ideological closer to the minority on the climate axis than more conservative parties. The analysis below suggests that this is due to cross-ideological accusations of political hypocrisy.

Topics of discussion

Topics in the COP26 discussion can be extracted using BERT topic modelling43 (Methods) and placed on the ideological spectrum (Fig. 4). See Supplementary Section 1I for the COP21 results.

Majority topics

Majority topics have a clear climate focus, making explicit reference to specific COP themes, including “women’s day”, “transport day” and “climate finance”. Beyond these, there are topics related to climate activism with a specific emphasis on youth protests, indigenous groups, the need for “climate justice”, and the “decolonisation” of climate change.

Potentially the most striking rift between users in the majority relates to whether they are COP supportive or not. Many pro-climate accounts are critical of the COP process, describing it as ineffective and accusing it of “greenwashing”. This theme is a clear shift from COP21, where only select influencers were COP critical (7% of labelled COP21 influencers; Supplementary Section 1D), most notably George Monbiot and Naomi Klein. Since then, criticism of the COP process has grown significantly (35% of labelled COP26 influencers).

Minority topics

The COP26 minority discuss a broad range of climate-related topics. Cross-referencing these with a taxonomy of “climate contrarian” claims37 shows that the COP26 minority promote and engage with all five of the leading contrarian claim types (Table 1).

Table 1 Common claims made by groups who oppose climate action and examples from the COP26 minority

Other topics not specific to climate include tweets critical of particular politicians, most notably Joe Biden (referred to as “sleepy Joe”), Boris Johnson (for promoting green policies) and Justin Trudeau (for allegedly destroying the Canadian oil/gas industry). Finally, there are topics of wider relevance to the political right, particularly COVID-19 (the “plandemic”), vaccines (“#NoVaccinePassports”) and illegal immigration (“[stop] illegal economic migrants”).

Political hypocrisy and the ideological divide

Understanding content that bridges the ideological divide is important for assessing which topics may act as a gateway into the ideological minority, particularly since Twitter recommends content on the basis of similarities in user–content interactions between accounts41. To assess this, we rank tweets according to the number of cross-ideological retweets—that is, majority author but minority retweeter, or vice versa. This reveals the theme of political hypocrisy, which includes references to the use of private jets and diesel cars, the continued use and development of fossil fuels, and the dumping of raw sewage. Half of all majority tweets referencing hypocrisy have been posted since December 2020 (Supplementary Section 1K and Extended Data Fig. 2).

News media reliability

Given the distinct topics discussed by the majority and minority, we may expect that these ideological groups reference different news media outlets. We show this using heat maps of ideology against independent news media reliability scores (Fig. 5 and Methods). This reveals that the ideological majority preferentially reference news domains with high trust scores, whereas the minority often reference domains with low scores. This result is robust if we use country-specific NewsGuard scores (Supplementary Section 1F). In Supplementary Section 1J, we show the formation of ideological echo chambers during COP, a common feature of polarized communities on social media9,27.

Fig. 5: The correlation of climate ideology with distinct media outlets.
figure 5

a,b, Heat maps showing the density of news media trust scores provided by NewsGuard, against the average ideological score of each media outlet’s Twitter audience for COP21 (a) and COP26 (b). Visualizations of the COP21 and COP26 network community structure are shown in Supplementary Section 1J, alongside heat maps illustrating the echo chamber effect27.

The wider climate discussion on Twitter

We now show that the COP discussion is broadly representative of the wider climate discussion on Twitter. This is important since keyword-based data collection using the search term ‘COP2x’ may fail to capture certain climate-related communities.

First, we cross-reference our COP dataset with two supplementary datasets: 1.3 million tweets using terms associated with climate scepticism, and all original tweets since 2012 using the term ‘climate change’ (Supplementary Section 1K). This reveals that (1) the activity of the COP26 minority is highly correlated to the activity of the broader climate-sceptic community on Twitter (Extended Data Fig. 3), (2) the COP26 minority started to engage with climate issues much more recently than the COP26 majority (Extended Data Fig. 4) and (3) climate-sceptic activity was very low, but present, before 2019. Note that there is no evidence of a change in the interaction rate between pro-climate and climate-contrarian groups (Supplementary Section 1K).

The expression of climate scepticism saw significant growth from 2019 onwards, peaking during the global climate strikes in September 2019 and the Australian bushfires in January 2020. This growth does not appear to have translated into significant engagement from sceptics during COP25, most likely due to its lesser importance (Fig. 1; major new agreements were not negotiated at COP25).

Increased sceptic activity does not necessarily imply an increase in the number of Twitter users with climate-sceptic views but more likely implies an increase in users expressing those views (which is in itself important). Possible drivers of this growth include (1) the issue of political hypocrisy (see above), specifically following the approval of a new Canadian oil pipeline in June 2019; (2) a backlash to the direct impact of the global climate strikes (minority content is particularly critical of Greta Thunberg and Extinction Rebellion); and (3) the belief that the climate movement is unreliable, with minority users blaming the Australian bushfires on arson, not climate change.

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