\makeatletter
\@ifundefined{HCode}
{\documentclass[screen,CRGEOS,Unicode,biblatex,published]{cedram}
\addbibresource{crgeos20240760.bib}
\newenvironment{Table}{\begin{table}}{\end{table}}
\newenvironment{noXML}{}{}
\let\citep\parencite
\let\citet\textcite
\def\xcitealp#1#2{\citeauthor{#1}, \citelink{#1}{#2}}
\newcommand*{\citelink}[2]{\hyperlink{cite.\therefsection @#1}{#2}}
\def\defcitealias#1#2{}
\let\citetalias\textcite
\let\citepalias\parencite
\def\thead{\noalign{\relax}\hline}
\def\endthead{\noalign{\relax}\hline}
\def\tabnote#1{\vskip4pt\parbox{.95\linewidth}{#1}}
\def\botline{\\\hline}
\def\dollar{\$}
\def\tbody{\noalign{\relax}}
\def\tsup#1{$^{{#1}}$}
\def\tsub#1{$_{{#1}}$}
\def\og{\guillemotleft}
\def\fg{\guillemotright}
\let\permil\textperthousand
\RequirePackage{etoolbox}
\usepackage{upgreek}
\usepackage{wasysym}
\usepackage{pifont}
\def\jobid{crgeos20240760}
%\graphicspath{{/tmp/\jobid_figs/web/}}
\graphicspath{{./figures/}}
\newcounter{runlevel}
\usepackage{multirow} 
\def\nrow#1{\@tempcnta #1\relax%
\advance\@tempcnta by 1\relax%
\xdef\lenrow{\the\@tempcnta}}
\def\morerows#1#2{\nrow{#1}\multirow{\lenrow}{*}{#2}}
\let\MakeYrStrItalic\relax
\def\refinput#1{}
\def\back#1{}
\csdef{Seqnsplit}{\\}
\newcommand*{\hyperlinkcite}[1]{\hyper@link{cite}{cite.#1}}
\makeatletter
\g@addto@macro{\UrlBreaks}{\UrlOrds}
\gappto{\UrlBreaks}{\UrlOrds}
\makeatother
\DOI{10.5802/crgeos.304}
\datereceived{2024-09-19}
\daterevised{2025-05-29}
\dateaccepted{2025-07-28}
\ItHasTeXPublished
}
{
\PassOptionsToPackage{authoryear}{natbib}
\documentclass[crgeos]{article}
\usepackage[T1]{fontenc} 
\usepackage{pifont}
\def\CDRdoi{10.5802/crgeos.304}
 \def\citelink#1#2{\citeyear{#1}}
 \def\xcitealp#1#2{\citealp{#1}}
\def\href#1#2{\url[#1]{#2}}
\makeatletter
\def\CDRsupplementaryTwotypes#1#2{}
 \def\selectlanguage#1{} 
 \def\hyperlinkcite#1#2{\citeyear{#1}}
\let\newline\break
}
\makeatother

\dateposted{2025-09-18}
\begin{document}

\begin{noXML}


\CDRsetmeta{articletype}{research-article}

\TopicFR{Sciences du climat}
\TopicEN{Climate Sciences}

\title{From hashtags to hostility: global dynamics of climate denialism
on Twitter in the post-COVID era}

\alttitle{Des Hashtags \`a l'Hostilit\'e : la dynamique mondiale du
d\'eni climatique sur Twitter \`a l'\`ere post-COVID}

\author{\firstname{David} \lastname{Chavalarias}\CDRorcid{0000-0001-9485-1399}\IsCorresp}
\address{Complex Systems Institute of Paris \^Ile-de-France, France}
\email[D. Chavalarias]{david.chavalarias@cnrs.fr}

\author{\firstname{Paul} \lastname{Bouchaud}\CDRorcid{0000-0002-0310-8194}}
\addressSameAs{1}{Complex Systems Institute of Paris \^Ile-de-France, France}
\email[P. Bouchaud]{paul.bouchaud@iscpif.fr}

\author{\firstname{Victor} \lastname{Chomel}}
\addressSameAs{1}{Complex Systems Institute of Paris \^Ile-de-France, France}
\email[V. Chomel]{victor.chomel@iscpif.fr}

\author{\firstname{Maziyar} \lastname{Panahi}\CDRorcid{0000-0002-3060-9883}}
\addressSameAs{1}{Complex Systems Institute of Paris \^Ile-de-France, France}
\email[M. Panahi]{maziyar.panahi@iscpif.fr}

\shortrunauthors

\keywords{\kwd{Climate disinformation}
\kwd{Socio-semantic networks}
\kwd{Astroturfing}
\kwd{Opinion manipulation}
\kwd{Polarization}
\kwd{Computational social sciences}}

\altkeywords{\kwd{D\'esinformation climatique}
\kwd{R\'eseaux socio-s\'emantiques}
\kwd{Astroturfing}
\kwd{Manipulation de lopinion}
\kwd{Polarisation}
\kwd{Sciences sociales computationnelles}}

\thanks{European project NODES (LC-01967516-CNECT/2022/5162608), 
CFM Foundation for Research.}

\begin{abstract} 
The rise of climate denialism in the general population ($+$5\% between
2019 and 2023) has been accompanied by a very significant increase in
denialist activism on ``X''/Twitter since the summer of 2022, and increased
hostility towards climate scientists.

Through global tracking of Twitter exchanges about climate change
between 2019 and 2023, as well as exchanges about COVID-19 pandemics,
we analyzed this online trend and its interaction with other societal
issues like politics and COVID-19 pandemics.

Beyond fact-checking, we show, through complex networks and semantic
analyses, that there are structural differences between these denialist
and pro-climate online communities, as well as between the circulation
of false information and other climate change-related narratives.

All the evidence suggests that the behavior of deniers is designed to
deceive, and that they are over-represented on social networks compared
to what they actually represent offline. This is particularly true on
``X''/Twitter since Musk's takeover.

We have also highlighted the globalized aspect of this new denialism,
its alignment with the interests and visions of powers such as Russia
and how it has benefited from the COVID-19 pandemic.
\end{abstract}

\begin{altabstract} 
La mont\'ee du n\'egationnisme climatique dans la population
g\'en\'erale (${+}$5 \% entre 2019 et 2023) s'est accompagn\'ee d'une forte
augmentation de l'activisme climatosceptique et du d\'eni climatique sur
X/Twitter depuis l'\'et\'e 2022, ainsi que d'une hostilit\'e croissante
envers les scientifiques du climat. 

Gr\^ace \`a un suivi mondial des
\'echanges sur X/Twitter concernant le changement climatique entre 2019
et 2023, ainsi que sur la pand\'emie de COVID-19, nous avons analys\'e
cette tendance en ligne et son interaction avec d'autres enjeux
soci\'etaux tels que la politique et la crise sanitaire.

Au-del\`a du
fact-checking, nos analyses des r\'eseaux complexes et s\'emantiques
montrent qu'il existe des diff\'erences structurelles entre les
communaut\'es en ligne n\'egationnistes et pro-climat, ainsi qu'entre la
circulation de fausses informations et d'autres r\'ecits li\'es au
climat. 

Tous les \'el\'ements indiquent que le comportement des
climato-d\'enialistes est intentionnellement trompeur, et q'uils sont
surrepr\'esent\'es sur les r\'eseaux sociaux par rapport \`a leur
pr\'esence r\'eelle dans la soci\'et\'e. Cela est particuli\`erement
vrai sur X/Twitter depuis la reprise de la plateforme par Elon Musk.

Nous mettons \'egalement en lumi\`ere le caract\`ere mondialis\'e de ce
nouveau n\'egationnisme, son alignement avec les int\'er\^ets et
visions de puissances telles que la Russie, et la mani\`ere dont il a
\'et\'e renforc\'e par les cons\'equences sociales de la pand\'emie de
COVID-19.
\end{altabstract} 

\maketitle

\vspace*{9pt}

\twocolumngrid

\end{noXML}

\defcitealias{witkowski_obscop_2023}{ibid.}
\defcitealias{chavalarias_toxic_2022}{ibid.}

\newcommand{\qot}[1]{``#1''}

\section{Introduction}\label{sec1}
Policies to combat climate change face a paradox\footnote{According to
IPCC, we define \textit{climate change} as anthropogenic shifts in the
global climate system.}. A sharp reduction in greenhouse gas emissions
is considered an absolute priority, with changes to our lifestyles and
behaviour as one of the main levers  \citep{ipcc_evidence_2022}. This
will only happen if public opinion is convinced that climate change is
man-made and can be combated by a change in collective behavior
\citep{huber_public_2020}.

But this seems to be less and less the case, although the consequences
of climate change are becoming increasingly apparent. According to a
\mbox{worldwide} longitudinal survey on 24k people from 30 countries and five
continents \citep{witkowski_obscop_2023}, the proportion of population
believing in anthropogenic climate change (ACC) has declined globally
from 69\% in 2019 to 63\% in 2022, with 9\% of the people surveyed
believing that there is no climate change at all, and  28\% believing
that it has only a natural origin or having no opinion about it.
Outliers States are the United States of America and Russia, with only
52\% of believers in ACC and France with the sharpest one year decline
(${-}$8\% between 2021 and 2022), with 63\% believing in ACC in 2022
(resp.\ 71\% in 2021), 8\% (resp.\ 9\%) denying climate change and 29\%
(resp.\ 20\%) denying its anthropogenic origin. 

It's to be expected that the presence of an increasing and significant
proportion of climate-denialists\footnote{In this article, we use 
``climate skepticism'' and  ``climate denialism'' interchangeably, the
second expression having the advantage of not referring to skepticism,
which is defended by some as a quality in science. See
\citep{jacques_general_2012} for more developments on this naming.} in
a country's population will lead to future climate measures being
contested, possibly violently. Understanding this global anachronistic
denialist trend is thus a major challenge for the efficient
implementation of future climate policies. 

Social networks such as Twitter/X could be both one of the factors
contributing to the rise of climate skepticism and a privileged view
point to observe and understand its evolution. For example
\citep{rogstad_is_2016, conway_rise_2015}  demonstrated the 
``symbiotic relationship'' that exist between social networks such as
Twitter/X and the media agenda, while \citep{wang_framing_2018} shows
that Twitter could contribute to frame the debate on societal issues in
advance of media coverage. On the other hand, computational science
studies have illustrated the power of large scale Twitter analyses to
depict opinion landscapes \citep{barbera_birds_2015} and their dynamics
\citep{Gaumont_2018,chomel_polarization_2022,chavalarias_toxic_2022}.

Twitter has been traditionally one of the main networks for
disseminating climate information from medias, NGOs, grassroots
activists, celebrities, and politicians \citep{fownes_twitter_2018}.
But times have changed and it is today at the very heart of the climate
denialist propaganda. Since 2022, climate crisis deniers have been
increasingly targeting scientists on this platform
\citep{fazackerley_climate_2023, vidal_valero_death_2023}, silencing
climate scientists which results in both boosting climate
disinformation\footnote{Arguments range from  \qot{climate change is
not real} to \qot{CO$_{2}$ is not a greenhouse gas}, to \qot{there is
no scientific consensus on climate change}, \qot{climate change is real
but caused by natural climate variability} or \qot{climate concerns are
part of a left-wing political agenda to destroy capitalism}  
\citep[see also][]{Coan_2021}. It should be noted that all these
arguments have made their way to the highest political circles and were
officially relayed in 2025 by the US Department of Energy 
\citep{Tollefson2025}.} and slowing down climate science
dissemination. A 2023 large scale \textit{Nature} survey of scientists
\citep{vidal_valero_thousands_2023} revealed that, while many said that
they had noticed an uptick in the amount of fake accounts, trolls and
hate speech, more than half reported that  ``they have reduced the time
they spend on the platform in the past six months and just under 7\%
have stopped using it altogether.'' At the collective level, following
low polarization of COP20 to COP25 debates on  ``X'',
\citep{falkenberg_growing_2022} reported an increase in polarization
during COP26 which was mainly driven by growing right-wing activity.
This context makes Twitter/X a particularly interesting vantage point
from which to study the rise of the climate denialism. 

Beyond fact-checking or the characterization of skeptics narratives,
this article aims to better understand the structural and
organizational specificity of denialist communities that enable them to
sustain themselves over time, as well as the factors that contribute to
the circulation of different denialist narratives at the global level.
To this end, we analyze the 2022 upsurge of climate denialism at the
global level through the Twitter lens with a special focus on two
outliers of this dynamics, the United States and France. 

\section{Data and methodology}\label{methodo}

\subsection{The Climatoscope database}\label{sec2.1}
Since 2015, we used the Twitter's track API to collect in real-time the
tweets associated to a list of several dozens of English and French
keywords related to climate change (see Supplementary Material~A). 
More than 400 millions tweets related to climate change were collected
until Twitter/X closed its APIs in spring 2023 (\textit{Climatoscope}
database). This data collection was not exhaustive but represents a
sufficiently large and diverse sample of the climate change Twitter/X
debates to understand the social dynamics driving them.

Similarly, we conducted a monitoring of the debates on COVID-19
(\textit{Covidoscope} database 2.5 billion tweets over 2019--2023,
77~millions being vaccine related) and on French politics
(\textit{Politoscope} database, 711~millions tweets over 2016--2023),
two independently collected databases that allow for cross-reference
between societal issues.

\subsection{Reconstruction of opinion landscape and\newline 
social
groups}\label{sec2.2}
We adopted a socio-semantic analysis approach to identify online social
groups associated to selected topics. Following  \citet{Gaumont_2018},
we used the intensity of retweets\footnote{The retweet is a message
that is relayed from account to account without modification
nor comment.} between
two accounts as an indicator of belief and representation alignment. In
short, the collection and analysis of millions of tweets and their
retweets makes it possible to build the network of interactions between
Twitter accounts. In these retweet networks, two accounts are linked if
one retweets the other intensively. Such  interactional approach to
social phenomena is performed without having to know the content of the
\break tweets.

By analyzing these interaction networks using graph theory tools, 
clusters or  ``communities'' can be identified, i.e.~groups of
accounts which productions reflect shared representations and common
beliefs on a given topic. We used the Louvain clustering algorithm
\citep{blondel_fast_2008} to identify the communities which has proved
suitable for this type of task \citep{Gaumont_2018}. For example, the
map of the entire climate change database for autumn 2022 is shown in 
Figure~\ref{fig:landscape2022}.  

\begin{figure*}
\includegraphics{fig01}
\caption{\label{fig:landscape2022}Climate Twittersphere in the fall of
2022. Mapping of 200k Twitter accounts retweeting climate
change-related content, in English or French. Each color indicates a
specific community, either geographic (country level) or ideologically
oriented (pro-climate science activists or denialists). Links
correspond to a retweet intensity equal to or greater than 7 over the
period. On the left: pro-climate/IPCC communities, on the right:
climate-denialists.}
\vspace*{-4pt}
\end{figure*}

This interactionist categorization of Twitter/X accounts makes it
possible to identify climate-denialist and pro-climate accounts, and
paves the way for new analyses of the social structure, strategies and
narratives of climate-denialist groups and their evolution.\looseness=1

Thanks to generic databases such as \textit{Politoscope}, we can
identify the different communities of opinion on more specific subjects
by applying this method to a filtered database whose messages are
filtered using certain keywords. Finally, these networks can be
visualized to highlight the social structures of these groups and the
relationships they maintain. 

\subsection{Detection of inauthentic behavior}\label{inauthentic} %2.3
\textit{Astroturfing}---the attempt to win the support of the general
public by artificially increasing the presence of an idea, person or
product in a population---takes a new dimension online with the
possibility to use automated accounts in opinion manipulation
campaigns. The line between the proselytizing of an automated account
or one operated by an actor paid to defend a cause and that of a
grassroot supporter of that same cause is often blurred. However, it is
possible thanks to machine learning techniques to assign a \qot{score
of inauthenticity} to an account based on its profile and online
activity, which would somehow give a probability for it to be
inauthentic. 

Drawing on publicly available datasets\footnote{Data aggregated by
Indiana University, as part of the
\href{https://botometer.osome.iu.edu/bot-repository/datasets.html}{botometer project}, 
containing thousands of bots involved in various online behaviors, such
as hyperactive political bots or fake accounts purchased from multiple
companies to increase a client's follower count.} and including tens of
thousands of accounts manually labeled as \qot{probably automated} 
(``bots''), we trained an AI model to assign an inauthenticity score to
a Twitter account based on the collected data and computed this score
for over 13 million accounts.

We decided to define as \qot{bot-like} the accounts having more than
50\% of chances to be inauthentic according to this method. Identifying
these accounts, however, is a race against the improvement of automated
techniques, and it is difficult to really assess the accuracy of these
methods without knowing exactly how advanced astroturfing techniques
are (see Section~\ref{inauthentic_behavior}).

Although we don't know the absolute level of performance of this
approach, we can still get insights by comparing the level of
inauthenticity between communities, or by analyzing its evolution for a
given community. A community with a higher average inauthenticity score
than others would point to possible \textit{astroturfing} operations.

\subsection{Toxicity of the tweets}\label{sec2.4}
\citet{bouchaud_crowdsourced_2023} have shown that toxic
\textit{tweets}---such as insults, threats or obscenity, are amplified
across the platform by Twitter's recommendation system, so that on
average they are ${+}$48.7\% over-represented in users' news feeds.
Moreover, \citet{chavalarias_can_2024} showed that Twitter-like
recommendation systems concentrate social power in the hands of the
most toxic users. The toxicity of online discourse is thus an important
dimension in understanding the over-representation of certain accounts
and narratives.

We employed Detoxify \citep{Detoxify}, an open-source natural language
processing model trained on Google's Jigsaw toxic comments database,
for the detection of toxic tweets. Significant attention was dedicated
to mitigating unintentional biases in the training process, notably
addressing racial biases, in accordance with the insights provided by
\citet{davidson2019racial}. The suitability of utilizing this model in
our study was affirmed through the manual annotation of randomly
sampled tweets from the aggregated dataset.

\section{Results}\label{sec3}
\subsection{The structure of the climate twittersphere}\label{sec3.1}
Since 2015, the mapping of English and French speaking activists on
climate change issues, regardless of time period, reveals a
bi-polarized social structure at the global level, with two major
regions clashing, one grouping Twitter communities that believe in
anthropogenic climate change, the other region is made up of
communities that dispute this fact---the narratives developed by these
communities will be referred to as \qot{denialists} 
(Figure~\ref{fig:landscape2022}).

Each of these regions has communities whose boundaries coincide with
geographic, political, or ideological borders. The largest and most
\mbox{stable pro-climate} science communities in this English/French speaking
landscape are Canada, the United Kingdom, Australia, France, Germany,
Pakistan, major international media (AP, Reuters, BBC, etc.),
international organizations (UN, COPX, UNICEF, NASA, etc.), climate
activists (Greta Thunberg, Greenpeace, etc.) and, \textit{last but not
least}, the United States of America, divided into two sub-communities:
the left wing of the Democratic Party-around Bernie Sanders and Alexandria 
\mbox{Ocasio-Cortez-,} and the \qot{mainstream} Democratic party
around Joe Biden, Kamala Harris and Barack Obama.

Overall, over the last few years (January 2021 to March 2023), the
core\footnote{Core of online communities are defined as those
communities detected on a graph whose links exceed a certain activity
threshold. For this study, we considered communities detected on the
interaction graph whose links represent a minimum of three to ten
retweets, depending on the extent of the reference period. For 
Figure~\ref{fig:landscape2022}, communities were detected with links of
strength 3 or more. Restricting the analysis to the core ensures a high
degree of accuracy in the categorization of accounts attitudes.} of
pro-climate accounts that we identified on Twitter are composed of a
little more than one million Twitter accounts that produced 51M tweets,
17.79\% of them being original tweets, the rest being retweets
(62.4\%), retweets with/of comments (13.39\%) or simply comments
(6.37\%). 

As for the denialist communities, the geographical structuring is
weaker, indicating greater coordination at the international level or
greater geographical concentration. On the one hand, we find Donald
Trump supporters and MAGA Republicans, accompanied by other leaders
such as those of UKIP in England, and on the other hand, a group of
influencers \qot{experts} in climate science, who have their own
audience and are densely connected to each other. It is in this latter
denialist community that one finds accounts notoriously supported by
the fossil fuel industries \citep{friedman_coal_2019}, such as the
Heart Land Institute or the Competitive Enterprise Institute. Last, a
small French denialist community had appeared during the year 2022
(${\approx}$10k accounts).

Overall, over the last few years (January 2021--March 2023), the
denialists communities identified on Twitter/X were composed of about
330,000 Twitter accounts that produced 20M tweets, 14.4\% of them being
original tweets, the rest being retweets (60.25\%), retweets with/of
comments (17.5\%) or simply comments (7.8\%).

\subsection{When Twitter descends into climate-denialism}\label{sec3.2}
The relationships between communities change over time, but overall,
the communities at the heart of the pro-climate science region, which
link all the others, are climate activists and to a lesser extent
mainstream media and news agencies. Over the period from Autumn 2019 to
Spring 2022, the proportion of denialist accounts was roughly stable
between 25\% and 30\%, which is consistent with sociological surveys
\citep{witkowski_obscop_2023}.

These digital communities are evolving social structures, both in terms
of their activity and their composition. Years of observation through
the \textit{Climatoscope} show that the intensity of the climate change
debate is locally modulated by extreme seasonal events that may be
linked to climate change (e.g.~Australian bushfires, extreme
heat waves or droughts), but it is also influenced by international
events such as the COP, political events such as the 2020 US
primaries---where the mainstream Democrats' agenda was challenged by
the left wing of the party (Bernie Sanders)---, or events with strong
societal impacts such as the COVID-19 pandemic. The latter caused a
significant drop in activity in all communities for a few months
(cf.~Supplementary Figure~B.1).

This relative stability between the pro-climate and denialist
communities was, however, challenged in July 2022, with a clear
resurgence of climate skepticism at the global level from July 20,
2022 as depicted on  Figure~\ref{fig:worldnumbers} and 
Supplementary Figure~B.2:
the relative weight of denialists communities on Twitter/X largely
increased to reach 50\% in December 2022 (against 37\% offline
\citetalias{witkowski_obscop_2023}). How is this evolution possible in a
period where climate change impacts have been more visible than ever?

\begin{figure*}
\includegraphics{fig02}
\vspace*{2pt}
\caption{\label{fig:worldnumbers}Worlwide evolution of number of
estimated core pro-climate and climate denialists accounts on Twitter
between 2021 and 2023. Data are averaged over a rolling week for better
readability.}
\vspace*{3pt}
\end{figure*}

The balance of power between digital communities is based on their
ability to keep their members mobilized and to recruit new ones. Each
of these phenomena has evolved in recent times on Twitter in ways
defavorable to pro-climate communities.

First, while pro-climate communities historically enrolled more new
members than denialist communities (i.e., accounts that were
contributing to their online momentum for the first time), the trend
has been reversing since April 2022 (cf.\ 
Supplementary Figure~B.2). A first
increase in relative denialist \mbox{recruitment} capacity occurred over the
period April--July 2022 with a spike of activity in July 2022 for both
pro-climate and denialist activists. For the former this correspond to
reactions to that month's extreme heat waves, and for the latter to
reactions following the release of a \textit{Project
Veritas}\footnote{\textit{Project Veritas} was an American far-right
activist group which used deceptively edited videos and secret
recordings in an effort to discredit mainstream media organizations and
progressive groups. It was among others financed by the  Donald J.
Trump Foundation and had close links to the Trump administration.}
video (cf.~Section~\ref{CNNExpose}). This video---featuring a
``CNN technical director'' talking about  ``instilling the next fear
(climate change) because COVID is no longer a fear factor to control
Americans''---illustrates the rise of conspiracy theorists who are
increasingly taking over the climate change debate and have become a
significant part of climate deniers on Twitter/X. As documented in 
Section~\ref{global_disinfo}, they are not there by chance and a
geopolitical explanation cannot be ruled out with potential links  to
propaganda operations by the Kremlin, whose hybrid war with Europe and
NATO intensified following its invasion of Ukraine. 

But the major alteration in relative recruitment capacities occurred
the weeks following Elon Musk's takeover of Twitter in October 2022. On
one hand, Musk's decreed an  ``amnesty'' for accounts previously banned
from the platform i.e.~for abusive behavior, harassment or
identity theft. This allowed super hate and misinformation spreaders to
return to the \mbox{network} \citep{milmo_elon_2022}. On the other hand Musk
changed Twitter's recommendation algorithm in a way that led to an
increase of the \textit{algorithmic negativity bias}
\citep{chavalarias_toxic_2022}, i.e.~the over-representation
of toxic content in users' news feeds, which jumped from 32\% to 48.7\%
\citep{bouchaud_crowdsourced_2023}. Given the increased toxicity of
climate denialists' tweets (cf.~Section~\ref{acute_toxicity}), this
has mechanically reduced the exposure of pro-climate messages and
increased that of climate skeptics, altering the ability of both
communities to recruit new \mbox{supporters.}

As for the capacities of communities to keep their members mobilized,
there has been a clear ``Elon Musk effect'' on pro-climate
communities. Immediately after Musk's takeover, the number of
pro-climate tweets halved and 33\% of pro-climate activists stopped
tweeting, along with 25.5\% of their supporters, while those who stayed
on Twitter reduced their number of daily messages by 33\% 
\mbox{(Figure~\ref{fig:worldnumbers}).}

In contrast, climate-denialists content producers experienced a weaker
than usual seasonal decline in mobilization (${-}$10\%) and daily
publication rate (${-}$11.2\%), while the activity of their relays even
increased slightly (cf.~Supplementary Table~B.1).  We can reasonably
assume that this silencing of pro-climate accounts is partly explained
by the perceived wave of  ``abuse and rude comments'' against 
climate
scientists since Musk's takeover \citep{fazackerley_climate_2023},
fostered both by the increase in the number of 
denialist accounts and
the increased visibility of their~posts due to a higher algorithmic
negativity bias.

Two preliminary conclusions can be drawn from the observation of these
global trends since 2022. First, Twitter/X has become an active place
of conversion to climate skepticism, as long as these new accounts are
not mostly fake accounts.  Second, Twitter/X is losing its status as a
globalized space for the expression of opinions on climate change, with
a desertion of people supporting the IPCC synthesis. These two
phenomena could reinforce each other, as the lack of contradiction
makes it easier for deniers to convert new accounts on Twitter/X.
Ultimately, this could also reinforce the offline pattern: 
\citet{witkowski_obscop_2023} has shown on a 30 countries survey that
climate denialism has gained 3\% globally in 2022, and up to 8\% in
France.

We will now investigate the structural differences between denialist
and pro-climate communities.

\subsection{Characterization of denialists communities}\label{sec3.3}
The communities of activists and the complex network they form are
mathematically reconstructed independently of the content of the
messages exchanged. The reason why denialist accounts are found in the
same community is that they mainly retweet each other. The same is true
for accounts supporting the IPCC conclusions. We can now draw on this
categorization to determine how these communities differ in terms of
their attitudes, skills, and the types of content they produce or
relay.

\subsubsection{Acute toxicity}\label{acute_toxicity} %3.3.1
The comparison of the toxicity of the tweets for different communities
reveals a glaring difference between the denialist communities and the
member of pro-climate communities. Performing a toxicity detection over
20k randomly sampled tweets either in the pro-climate or denialist
communities, at the global scale, we reveal that the later produced on
average 2.75 times more toxic tweets than the former with some
geographic variations. For example, the proportion of messages
identified as  ``toxic'' circulating in the French denialist community
is 3.5 times higher than that of the French IPCC community, and 1.5
times higher than that of pro-sufficiency community 
(cf.~Supplementary Figure~D.4). 

A public report presenting preliminary results of this study was
published online in \citep{Chavalariasetal2023}. We collected 7718 original tweets
published within twelve days in reaction to this publication, 1604
being produced by accounts categorized in 
Figure~\ref{fig:landscape2022}. These tweets have generated a total of
2.4M impressions, 1.3M retweets, 17.7k likes and discussions involving
3920 replies and 400 quotes. The over-toxicity of reactions of the
denialist community reached ${+}$373.3\% compared to the IPCC community
(see Supplementary Figure~E.1 and 
Supplementary Table~E.1), with estimated weights of
60.88\% for  ``insult'',  23.71\% for  ``obscene'' and 5.71\% for 
``identity attack'' contents. This is a modest illustration of what
climate scientists face when they try to combat online climate
\mbox{denialism.}

\subsubsection{Inauthentic forms of expertise and\newline 
concentration of
social power}\label{expertise} %3.3.2
Since it is difficult to have extensive expertise in distinct domains,
it is reasonable to expect that the number of people able to talk about
two different topics with a certain level of expertise will decrease as
the required level of expertise increases.

This intuition can be formalized with the multi-expertise
index\footnote{The measure of multi-expertise on two topics $a$ and $b$
is simply the normalized proportion of accounts using both arguments at
least $n$ times, $n$ being the expertise threshold, among all users
using at least one of them (Jaccard index) \citep{chomel_beyond_2022}.}
developed in \citep{chomel_beyond_2022}, which indicates the extent to
which multi-experts are present in a given community (see also 
Supplementary Material~J).

By quantitative and qualitative analyses of tweets, we first identified
the narratives most often used by members of the various Twitter
communities over a six month period in 2019 in order to identify their
favorite topics. For the denialist community, we focused our analysis
on the following narratives: the influence of the sun, the natural
variability of the climate and its cycles, the fact that CO$_{2}$ would
be beneficial for plants and the planet, or the idea that global
warming is simply a good thing. For the pro-climate science community,
we have identified narratives such as the greenhouse effect, melting
ice, rising sea levels, and bush fires.

\begin{figure*}
\includegraphics{fig03}
\caption{\label{fig:jaccard}Jaccard index based on retweet threshold,
calculated on online discussions that took place on Twitter in 2021.  A
high jaccard index for a high threshold means that the exact same
accounts are tweeting or retweeting about the two topics with high
volume (see Supplementary Material~J).}
\end{figure*}

For each of the topic pairs and each of the communities, we computed
the multi-expertise index, whose variations as a function of the
required expertise threshold are presented in 
Figure~\ref{fig:jaccard}. The pro-climate science community has an
expected expertise profile (Figure~\ref{fig:jaccard}a): most vocal
accounts on one topic are not vocal on the others (or not to the same
extent). This could be explained by the fact that only the \qot{true}
specialists of a given subject speak frequently on this subject, and
speak much less on the other subjects. As for the other members of
these communities, if they were to speak about several subjects, it
would only be very occasionally for each of them (for example in
reaction to extreme events related to climate change).

The denialist community exhibits a very different and somewhat
anomalous expertise profile. While for low levels of expertise, the
same initial decrease in the multi-expertise index is observed as a
function of the required expertise threshold, there is a sharp increase
in this index for high expertise thresholds 
(Figure~\ref{fig:jaccard}b). Therefore, there are accounts
that speak on all topics in large quantities. Either these topics are
not really technical and, given the complexity of earth systems, do not
contribute much to the debate, or these denialists speak on topics
regardless of their actual knowledge of them. Either way, instead of
having prescriptive power distributed across many specialists as in the
pro-climate community, there is a small group of accounts within the
denialist 
\mbox{community} that concentrates the presumed expertise and
fabricates the majority of the narratives that circulate there.

\subsubsection{A higher density of accounts with inauthentic
behavior}\label{inauthentic_behavior} %3.3.3
The global proportion of bots on Twitter is estimated between 8\% and
18\% by 2022 \citep{fukuda_estimating_2022} and it is quite easy to buy
fake Twitter accounts, operated by humans or robots, which will act
according to the wishes of their buyers (see for an example the 2023
\qot{Team Jorge} case \citep{kirchgaessner_how_2023}). 

For this reason, \textit{astroturfing} is a very popular strategy for
some actors \citep{chavalarias_unlikely_2016}.  With the arrival of
conversational artificial intelligence such as ChatGPT, which reduces
its costs while increasing its effectiveness
\citep{hsu_disinformation_2023, goldstein_generative_2023}, an
intensification of this practice is to be expected.

We have estimated the proportion of \qot{bot-like} accounts in climate
change discussions to be about 3.5\% in the global pro-climate
community when it approaches 6\% for the global denialist community
(${+}$71\% in comparison with the pro-climate community). As pointed 
in Section~\ref{inauthentic}, 
these  figures are probably underestimated but relative proportions of
\qot{bot-like} accounts between communities and their evolution is
informative.

The proportion is not uniform within the different sub-communities. For
example, it is estimated at 10\% in the Indian pro-climate community
accounts but at only 1.8\% in the British pro-climate 
\mbox{community.}

As for the evolution, two indicators point to an intensification of
astroturfing practices since 2022. First, the yearly proportion of
account creation with inauthentic behavior in climate exchanges has
seen a sharp increase between 2020 and 2022 globally on Twitter
(cf.~Supplementary Figure~B.3). As we collected the tweets in real
time, this means either that there has been an increase in the creation
of such accounts over the last few years, or that this type of account
is used in turn on different subjects and that the oldest ones were
more likely to be detected and deleted by Twitter as they were
campaigning on subjects we didn't monitor.

Second, there has been a steady increase in the proportion of 
``bot-like'' active accounts since the end of February 2022.  For the
North America and Australia communities the increase was of ${+}$400\% by
the end of 2022 compared to the end of 2021 (see 
Figure~\ref{fig:astroturfingOp}a). The same phenomena is observed for
France (cf.~Supplementary Table~D.1). 

\begin{figure*} 
\includegraphics{fig04}
\caption{\label{fig:astroturfingOp}{Astroturfing operations}.
({a-left})~Evolution of the proportion of  ``bot-like'' accounts
for North America (USA and Canada) and Australia;
({b-right})~Anomaly in the creation dates of the accounts that
participated to the \#CNNExpose operation during the period July 20--21,
2022.}
\end{figure*}

Last, as demonstrated in  Section~\ref{global_disinfo}
(Figure~\ref{fig:polar}), the most influential accounts in the core
denialist community behave almost exactly like the rest of the group on
a wide range of topics at various times, which is a sign of
coordination.

In short, climate skeptics use inauthentic accounts and bots to
propagate their ideas far more than any other actors in the climate
debate, and this practice is intensifying since February 2022.

\subsubsection{Opinion and platforms' algorithm manipulation through
planned astroturfing operations}\label{CNNExpose} % 3.3.4
By focusing on the level of activity on certain topics of discussion
rather than interactions among accounts, the denialist community
community reveals a very particular form of social organization that
relies on the ability of a few to influence the flow of information, a
form of organization already documented in other fields
\citep{starbird2017examining}.

We identified two different strategies: repeated operations over longer
periods that use repetition bias to make a narrative plausible to those
exposed to it; and massive operations over short periods to influence
recommendation algorithms. 

An example of the former is detailed in 
Supplementary Figure~G.1. An example of
the latter is provided by a detailed analysis of the climate denial
wave of July 20, 2022. It gives insights into both the scale of these
practices and the extent to which the proportion of fake accounts could
be underestimated.

July 20, 2022 saw the emergence of a narrative that had been
circulating only quietly until then, namely that CNN and the U.S.
government were planning  ``to instill the next fear [Climate change]
as COVID is no longer a fear factor in controlling Americans.'' This
narrative was based on a video first published  on
YouTube\footnote{\url{https://www.youtube.com/watch?v=Dv8Zy-JwXr4}.} on
April 13, 2021 by far-right group \textit{Project Veritas}. It features
a  ``CNN Tech director'' who had supposedly been trapped on hidden
camera. We identified most variants of this narrative and analyzed the
corresponding tweets captured by the climatoscope\footnote{Climatoscope
query ${=}$ climat* AND (``CNN tech director'' OR  ``CNN technical
director'' OR  ``CNN director'' OR ``CNN employee'' OR ``CNN guy'' OR 
``CNN producer'' OR ``directeur de CNN'' OR  ``directeur technique de
CNN'' OR  ``project Veritas'' OR ``CNN leaks'' OR (fear AND CNN)).} in
order to analyze its 
\mbox{propagation.}

Although a first rumor surfaced in the U.S. as early as January 1,
2022\footnote{See
\url{https://twitter.com/LetsgoBrandonDE/status/1477127280044482566}.}, with
an average of 6 tweets per day between January and July 2022, this
narrative did not get much traction on Twitter until July 20, 2022
with only 1281 accounts in total participating to its diffusion so
far. Suddenly, between July 20, and 21, the number of tweets
skyrocketed to more than 22k per day involving 43.3k accounts before
quickly fading out (see Supplementary Figure~F.1-3).

Not only is this pattern of activity highly inorganic, but the study of
the 43.3k accounts' profiles that took part in this narrative burst
leads to other troubling elements. While there is less than a dozen
accounts with same creation day on average, more than 1807 of them
(4.17\%) have been created in just one week between 2022-04-25 and
2022-04-30 (cf.~Figure~\ref{fig:astroturfingOp}b). This
means that most of these accounts are fake accounts created few months
before the operation for the purpose of astroturfing. Creating a cohort
of astroturfing accounts with such a statistical anomaly is a gross
error, and we can reasonably assume that the proportion of fake
accounts among the 43.3k accounts that took part in this operation is
much higher than this 4.17\%.

Indeed, among those 1807  accounts, only 126 are characterized as
\qot{likely-bot} by our bot detector and only 189 were suspended by the
Twitter Moderation Research
Consortium\footnote{\url{https://transparency.twitter.com/en/reports/moderation-research.html}.}, 
which was supposed to remove content and accounts violating the
platform's manipulation and spam policy, before ``X'' put an end to
its moderation program. On the assumption that accounts have been
suspended by Twitter because of their inauthenticity, this means that
only about 10\% of accounts used for astroturfing practices are
identified either by Twitter or by state-of-the-art AI bot detectors.
Since there are 2205 suspended accounts among the 43.3k, we can
estimate the order of magnitude of the proportion of fake accounts that
took part to this astroturfing operation to near 50\% (21k accounts).
This is more than enough to manipulate Twitter/X trends
\citep{chavalarias_toxic_2022} and get some Twitter/X users outside the
denialist community to relay this story. 

This case study illustrates both the astroturfing practices of these
communities and the scale of their digital army: a low-key
dissemination of a narrative, followed by a  ``one-two punch''
operation to impose it on the recommendation algorithms and some of the
users of a social network, insisting in the process that it has been
hidden from the public for\break months.

Last, it should also be noted that both phases of dissemination take
advantages of a globalized space. The second phase, more intense,
feature messages in English, French, Italian and Dutch in the case
studied. As for the first phase, although the very first tweets on January
1, 2022 came from an apparently U.S. citizen (see   Supplementary
Figure~F.4), French accounts also contributed as soon as January 14,
2022 (see  Supplementary Figure~F.5) as well as to the bootstrap of
the second phase on July 17, with for example the participation of
the @Elpis\_R account  (Supplementary Figure~F.6).

This last account occupied a particular position in the French
informational landscape in 2022 and the detailed analysis of its
messages reveals an other important aspect of the new climate
disinformation and denialism trends.

\subsubsection{Opportunism and the connection of global\newline
extremes}\label{sect:elpis} %3.3.5
@Elpis\_R is not just an insider in U.S.\ denialist narratives, it is
also the main influencer who structured the new denialist community in
France at the summer 2022. Both the \textit{PageRank} or the
\textit{eigenvector centrality}, two  metrics from graph theory used to
measure influence in a network, rank this account first during summer
2022 in the French part of the landscape depicted by 
Figure~\ref{fig:landscape2022}  (see also 
Supplementary Figure~C.1).

This account is anonymous and has a male profile picture retrieved from
an image bank (see   Supplementary Figure~H.2). For this reason, we
will refer to this account with  ``he/his/him'', although there is no
guarantee that this account is owned by one and the same person. It was
created in July 2012, but had only 27 followers in September 2021,
which means that it was dormant between 2012 and 2021.

As of 2023-10-08, \textit{Elpis\_R} defines himself as 
``\textit{Climate Science Research---Climate Realist---Alarmists Ignore
The Geological Climate  Record.}''\footnote{Note that although all his
posts are in French, his profile is in in English with elements of
language borrowed from American denialists.}.

By reconstructing the network of interactions of \textit{Elpis\_R} from
the global data of the climatoscope (all second neighbors), it appears
that this account serves as a bridge between the French information
space and the community of English speaking climate deniers (cf.\ 
Figure~\ref{fig:ElpisNeigh}). If this is not sufficient to attribute
any geographical origin to it, it nevertheless points to a convergence
of interests at an international level in climate misinformation, as it
has already been documented on other subjects such as COVID-19 
\citepalias[see][]{chavalarias_toxic_2022}.

\begin{figure*} 
\includegraphics{fig05}
\caption{\label{fig:ElpisNeigh}Core of the information flow network
between U.S. and French denialists (dense network of second neighbors
of @Elpis\_R with at least three links to other members of this group).
Pink and red communities are French speaking, orange communities are
English speaking.}
\vspace*{6pt}
\end{figure*}

To defend its point of view, the account \textit{Elpis\_R} uses a
rhetoric that can be analyzed with the  ``4D'' approach, developed to
investigate Kremlin propaganda \citep{nimmo_anatomy_2015}, (see 
Figure~H.3): \textit{Dismiss} (\qot{if you don't like what your
critics say, deny the allegations on the ground, or denigrate the one
who makes them}), \textit{Distort} (\qot{if you don't like the facts,
distort them}), \textit{Distract} (\qot{if you're accused of something,
turn the attention away by launching accusations elsewhere}),
\textit{Dismay} (\qot{if you don't like what someone else is up to, try
to scare them}). In particular, \textit{Elpis\_R} specifically attacks
IPCC members as well as climate science scientists, with several daily
posts, some of them very technical.

He complements these 4Ds with a fifth that is perhaps the most
important in promoting climate inaction: \textit{Doubt}
\citep{oreskes_merchants_2010}. 

\textit{Elpis\_R} is also one of those accounts that spread
contradictory messages, such as  ``there is no global warming'' along
with  ``the climate has always changed and warming is not due to our
emissions''  
(Supplementary Figure~H.2). When someone pointed this out to him,
the interaction came to a screeching halt, proving that this was not an
attempt to convince on the basis of proven facts.

His climate activism is however quite recent.  As shown in 
Figure~\ref{fig:ElpisEvol}, prior to the spring of 2022, this account
had a long period of anti-vaccine activism, with the transition between
these two periods taking place through a phase where he was the
discreet relay of the pro-Kremlin propaganda that flooded the social
networks at the beginning of the war in Ukraine. In fact, before
defining himself as \qot{Climate Science Research (Independent)}, he
defined himself between 2021-12-23 and 2022-06-10 as
\qot{Biostatistician, (data analyst)} and indicated at other times in
his profile wanting to \qot{Reinform against this Orwellian
propaganda}, or to be a \qot{Free spirit, for a fair information and
not biased by the systemic corruption which gangrene this  world}.  
Supplementary Material~H.1 provides the full history of his
profile description, a timeline that is only accessible to those who,
like us, did record tweets and their associated profile descriptions on
the fly.

\begin{figure*} 
\includegraphics{fig06} 
\caption{\label{fig:ElpisEvol}Daily number of messages from the account
\textit{Elpis\_R} on some key topics. Warnings: the plot of messages
relaying Kremlin propaganda has been drawn on another scale for
questions of readability. All Elpis\_R messages were retrieved using
Twitter's public API before it was shut down. Key words used to define
the topics (originally in French):  \textit{Climate}---``CO$_{2}$'', 
``warming'',  ``climate''; \textit{IPCC}---IPCC, GIEC; 
\textit{Covid}---``covid'', ``vaccination'',  ``vaccine''; 
\textit{Russia}---``Putin'',  ``russia'', ``ukraine'',  ``Zelensky''.}
\end{figure*}

One of his profile description even once referred to his profile on
Gettr, a microblogging platform popular with the American far right and
on \href{http://VK}{vk.com}, the Russian Facebook controlled by the
Kremlin \citep{nast_how_2022}, that he has since deleted. A snapshot of
Nov 8 2021 by the
WayBackMachine\footnote{\url{https://web.archive.org/web/20211108200828/http://vk.com/real\_elpis}.} 
of his VK homepage shows that of the nine archived messages posted by
\textit{Elpis\_R} on its wall between 3/07/2021 and 11/10/2021, eight
were  ``vaccin alarmist'' and one warned about the impending food
shortage due to the pandemic. Nothing on climate change.

\begin{figure*}
\includegraphics{fig07}
\caption{\label{fig:antivax}Core activists common to the COVID and
climate debates. The split of the COVID-19 landscape into geographical
communities is also given (right side) to highlight the multi-country
alignment. The climate change data collection focused on messages in
English and French, which explains why other languages are
under-represented in this visualization.}
\end{figure*}

\textit{Elpis\_R} thus appears to be an opportunistic anonymous
account, whose real motivations are obviously not those displayed in
his profile. He has jumped from one divisive debate to the other but it
is however his climate denialist period which allowed him to gain in
visibility in France, making him pass in few months, from less than
1000 followers (July 2022) to more than 25.5k in 2023.

\subsubsection{Globalized, multi-topic
disinformation}\label{global_disinfo} % 3.3.6
The multi-topics opportunism of \textit{Elpis\_R} is not an isolated
case nor specific to France. We have been independently monitoring the
English and French speaking COVID-19 Twitter debate since 2020 and
could  map the full COVID-19 Twitter landscape in these two languages
over the period January 2020 to June 2021 (core composed of 157k accounts
for 40M tweets, see  
Supplementary Material~I). The structure of
the COVID-19 landscape (period 2020--2022)  is different from the one of
the climate: a core formed by the bi-pole of US pro-vaccine vs.\ 
``anti-sanitary dictatorship''/anti-vaccine accounts, with a replica of
this dipole structure for each country. Although the  confusionist
covid-19 ``antivax'' communities form a less coherent global structure
than for climate change, there is a significant flow of
(dis)information between the main alt-right/anti covid-19 vaccine
community in the USA toward other communities in other countries
(cf.~Supplementary Figure~I.1).

Tweets about climate and Covid-19 have been collected independently
within two separate digital observatories. Moreover, the focus period
of this climate change study (2021--2023) only partially overlaps the
``hot'' period for the Covid-19 database (2020--June 2021). There are
however accounts that appear in both databases. Cross-referencing the
two debates, we found ${>}$96.3k worth of accounts that talked about both
climate change and Covid-19 between 2020 and  2023.
Figure~\ref{fig:antivax} shows their ideological alignment. This
analysis reveals a clear pattern: in every country involved in this
analysis (here mainly USA, UK, France, Netherlands, Italy), all 
confusionist covid-19 ``antivax'' accounts who also took part in the
climate debate where, except few exceptions, denialists and vice versa.
This means that there is a global alignment between anti-Covid-19
vaccine attitudes and climate denialist attitudes. What's more, in
France, since climate denialist communities only emerged after the
pandemic was over, we can deduce that the pandemic created fertile
ground for the development of very powerful anti-system communities
with conspiracist  and confusionist tendencies, which then converted to
climate denialism under the influence of their leaders. Consequently,
all we had to do to anticipate future disinformation actions was take
the opposite of what the \textit{Project Veritas} fake news announced
at spring 2022: the Covid-19 disinformation campaigners were about to
become climate change disinformation campaigners as the Covid-19
epidemic comes to an end.

This opportunistic pattern of mobilization is not an isolated case.
Among French climate activists accounts identified in the Climatoscope
a significant proportion of accounts representing 53.1k 
accounts are also active in politics and can be identified in the
Politoscope: 96.5\% of the core of French climate deniers  (9.2k
accounts), 77.4\% of the core of IPCC aligned accounts (15.6k
accounts),  77.8\% of the core of techno-solutionist group (6.2k
accounts), those core communities being mapped on  Supplementary
Figure~C.1.

We can see that climate deniers over-invest in politics. To describe
their contribution to the political arena, in addition to their
involvement in anti-covid vaccine polemics, we have analyzed their
participation to some other divisive issues studied with the
Politoscope \citep{chavalarias_minuit_2024} (see  
Supplementary Material Section~K for
their precise definition). The selected issues are  ``Islamo-leftism''
(50.6k accounts),  ``Great replacement \mbox{theory''} 
\mbox{(35.9k~accounts),} 
``Israeli-Palestinian conflict'' 
(39.8k accounts), ``Jean-Michel
Trogneux'' (21.6k accounts),  ``Anti-wokism'' (5.3k accounts) and
``Kremlin propaganda'' (62.4k accounts). The social groups identified
in the politoscope database over 2020--2023 are the far-right
communities (\textit{Rassemblement national} and \textit{Reconqu\^ete!};
69k accounts in total), the
\textit{Patriotes}\footnote{\textit{Patriotes} is a fringe confusionist
far-right political community, one of whose leaders is Marine Le Pen's
former right-hand man, formed in reaction to the discovery of a vaccine
against covid-19. It has no weight in the pool but has one of the
largest Twitter community \citep[cf.][]{chavalarias_toxic_2022}.} (74.7k
accounts) and 	all other political 
\mbox{communities} that we aggregated in a
group labeled ``All but far-right'' (458.8k 
accounts). To give an order
of magnitude, we identified 602k accounts in the Politoscope (mostly
French accounts) between 2020 and 2023 that belong to clearly
identified communities while we identified 138k accounts (most English
and French speaking accounts) in the Climatoscope over the period 2021
to 2022, that were categorized either as pro-climate or as deniers.
53.1k accounts are common to these two database samples, making it
possible to cross-reference political affiliation with attitudes to
climate  change.

We compare the involvement in politics of French deniers  with a
reference group formed by IPCC aligned communities from the
Climatoscope database over the same period (20.2k accounts),
i.e.~the union of the mainstream media community, the IPCC
community and the pro-sufficiency 
\mbox{community.} 
These three communities
form a super-cluster of French pro-climate accounts (cf.\  
Supplementary Figure~C.1) which have in common that they are not opposed to
sufficiency, and that they recognize the reality of ACC.  We also
computed this involvement for the top 10\% of the most influential
deniers accounts in terms of pageRank to assess the profile of the
group's  leaders.

As it can be seen on  Figure~\ref{fig:polar}, the common characteristic
of the core climate denialist community is that it invests
opportunistically in divisive issues compared to the reference group of
IPCC-aligned communities (20k accounts): 84.5\% contributed to
anti-vaccine propaganda (8.45 times more than the reference group),
59.4\% to exchanges about the Israeli-Palestinian conflict (3.36 times
more than the reference group), 47.1\% to great replacement theory
propaganda (25.9 times more than the reference group), 44.7\% to the
promotion of ``islamo-leftism'' concept (12.7
times more than the
reference group), 17\% to ``anti-wokism'' movement (36.7 times more
than the reference group). 94\% of core climate deniers are involved in
far-right groups (see also   Supplementary Figure~D.5): 20.8\% 
in the \textit{Rassemblement national} or \textit{Reconqu\^ete!} communities
and 73.2\% in the \textit{Patriotes} (vs.\ 3.81\% for the reference
group). But what is most striking is their involvement as relays of
Kremlin propaganda. More than 80\% of them have relayed at least once
some Kremlin narratives about NATO, the Ukraine war or President
Zelensky, this estimation being a lower bound. In comparison, only
5.48\% of the reference group had done  so.

\begin{figure*}
\includegraphics{fig08}
\caption{\label{fig:polar}Involvement of the French climate denialist
accounts in other divisive societal issues and extremes political
groups (see  
Supplementary Material Section~K for their description). Involvement in a
topic is defined as the proportion of climate deniers who have also
contributed to that topic on Twitter/X.  Level of involvement for the
10\% of the most influential accounts (yellow) as well as for all 
climate denialist accounts (red) can be compared to the one of
pro-climate accounts that do not oppose to sufficiency (blue) which
correspond to the mega-cluster of  
Supplementary Figure~C.1. made up of the IPCC
community, the media community and the community of pro-sufficiency 
advocates. The fact that the top 10 most influential accounts behave
almost exactly like the rest of the group on such a wide range of
subjects and at such varied times indicates a very high degree of
coordination among climate deniers, which is a sign of inauthenticity.}
\vspace*{-2pt}
\end{figure*}

\section{Discussion}\label{sec4}
We investigated at climate denial through the prism of Twitter/X.
Although Twitter/X is not representative of the general population, it
was home to some of the most influential figures in public life and, by
working with long time series data, we can assess trends in climate
change denial, investigate the structure of denialist groups and the
evolution of their strategies.

Climate denialism has many facets, each of them often developed by a
small number of actors whose true motivations are generally masked. The
best-known and historically most active is supported by the fossil fuel
industries, which have an economic interest in delaying action against
climate change \citep{oreskes_merchants_2010, brady_exxon_2021}. Their
involvement in online climate disinformation has been revealed on
several occasions, including recently following the bankruptcy of an
American coal company \citep{friedman_coal_2019}. 

Another strand of climate skepticism is  politically motivated and is
historically  associated to conservative ideologies
\citep{oreskes_merchants_2010}. Indeed, we observed that one of the
world's largest climate-skeptic communities was made up of MAGA
activists who were particularly active during election campaigns (cf.\ 
Figure~\ref{fig:landscape2022} and Supplementary Figure~B.1).

Ultimately, these two trends in climate denialism have a seasonal
activity that peaks when the news deals with extreme climatic events in
the case of the former, or election campaigns in the case of the
latter.

But a new globalized trend that doesn't follow these patterns has
recently been added to the landscape. Involving activists from the
American alt-right, the French far-right  and Kremlin's propagandists
among others it contributes to a globalized circulation of narratives
and is made up of opportunistic accounts accustomed to social conflict.

Climate denialists stand out for the type of disinformation they
produce: a high degree of toxicity in their messages, fake expertise, a
high degree of coordination across topics, an abnormal proportion of
\qot{probably bots} or inauthentic accounts---mobilized for astroturfing
operations and manipulation of the platform's algorithms---and a
tendency to relay conspiracy theories and Kremlin propaganda.

Although the conspirationist and confusionist approach to climate
change has been active for years \citep{uscinski_climate_2017}, we
should not understate the particular context in which this trend is now
unfolding. First, we are in a post-pandemic world that has witness an
unprecedented growth in online anti-system and conspirationist
theories. These theories have been favored by two years of fears and
uncertainties engendered by the pandemic and the scale of the
restrictive and often liberticide measures that had to be put in place
by governments to contain it. This situation has provided fertile
ground for the development of very powerful digital communities
\citep{chavalarias_toxic_2022}, which are now being re-mobilized on the
climate denialism front by leaders seeking to maintain an audience. 

We also live in a world where authoritarian states such as Russia have
long been waging a permanent hybrid war on social networks with the
strategy of amplifying divisions within democracies in order to weaken
them \citep{schoen_putins_2016, colon_guerre_2023,
linvill_russians_2019, howard_ira_2019}. This cyberwar has been
amplified by the Ukraine war with a surge of online Kremlin's
propaganda on social network
\citep{oecd_disinformation_2022,geissler_russian_2023,
chavalarias_minuit_2024} and the emergence of fossil fuels as the bone
of contention in economic sanctions against Russia.

Last, restricting the focus to Twitter, the situation is exacerbated by
Elon Musk's choices \citep{chavalarias_elon_2025}, which have made this
network a major forum for climate denial and proselytizing.

The issue of climate change is an area where governments are being
urged by a part of the  of the population to take strong actions,
involving major changes in the lifestyles of all citizens. Many of them
will only accept these measures if the results are worth it. Instilling
doubt and misinformation about the reality of climate change in some
communities, while heightening awareness of the climate emergency in
others, is therefore a very effective way to destabilize governments by
placing them at the center of conflicting demands from their citizens.
Whatever the policy adopted, social revolt is guaranteed and violence
can steam from all sides.

In Januray 2025, Poland's military counterintelligence service
revealed that ``Russia is intensifying its disinformation activities
on the climate crisis. Increased activity in this regard has been
observed since the outbreak of the war in Ukraine. It affects the
entire European Union, with a special focus on Poland''
\citep{grostern_russia_2025}. Although it is impossible, with the data
available to us, to prove the exact origin of the climate
disinformation, they do suggest that former Russian disinformation
channels and actors are now being used to spread disinformation about
climate change and attack climate scientists\break  globally.

Putin is known for its climate denialism
\citep{tynkkynen_climate_2018,ashe_russian_2022} and his support to
far-right occidental groups \citep{futak-campbell_political_2020}. It
would have been a major strategic mistake not to take advantage of this
opportunity in his roadmap to undermine Western  democracies.

Sowing division through online interference is inexpensive and
risk-free for would-be agitators because, unlike in dictatorships, it
is not illegal to engage in this kind of activity within democratic
regimes. Having at their disposal powerful digital communities
inherited by the pandemics and eager to rebel against the  ``system''
in place is an unhoped-for opportunity.

Donald Trump's second term in office has given these anti-establishment
actors an unexpected ally: the US administration, whose officially
climate-denialist policy directly attacks climate science and
climatologists \citep{Voosen2025}, and whose Department of Energy
includes in its reports the climate-sceptic theories that until now had
been circulating in the depths of the Internet \citep{Tollefson2025},
some being referenced in this paper.

We consequently must expect that the low-risk, high-gain amplification
of climate-denialism and conflicts linked to the fight against global
warming to be further exploited in the  future.

\section{Conclusions}\label{sec5}
The rise of denialism in the general population has been paralleled by
a very significant increase in climate denial activism on Twitter/X
since the summer of 2022.

Beyond fact-checking, we've shown that there are structural differences
between these deniers and pro-climate online communities, as well as
between the circulation of misinformation and other climate
change-related narratives. 

All the evidence points to the idea that the behavior of denialists is
deceptive adn coordinated, and that they are over-represented on
Twitter/X compared to what they actually represent offline,  especially
since Musk's takeover. This probably also applies to other social
networks.

We have also highlighted the globalized aspect of this new climate
denialism, as well as how it has benefited from the pandemic and the
alignment of its protagonists with the interests and visions of powers
such as Russia and, since Donald Trump's second term in office, the
United States.

So it's no coincidence that we're witnessing a resurgence of climate
skepticism at a time when it's becoming indisputable that global
warming is man-made. Not only must the fossil fuel industries redouble
their efforts to slow down the implementation of measures that are
becoming increasingly urgent, but climate change issues are becoming an
active field of subversion for actors for whom the deterioration of
living conditions on Earth is nothing compared to the prospects of
strengthening their power. 

Division is an effective strategy for conquering power, theorized
millennia ago by Sun Tzu in \textit{The Art of War}
\citep{griffith1963sun}, which during the Cold War was the bedside
guide of KGB officers. It's hard to say how effective this strategy
will be in weaponizing climate change, but one thing must be said: it
loses much of its effectiveness when revealed to the public.

This is why it is imperative that independent players, including the
scientific community, are able to analyze and publicize the large-scale
manipulation of the digital information space. Given the tendency of
very large online platforms such as Twitter/X to close off access to
their data, this is another anachronistic trend that needs to be
addressed. The fight against climate misinformation will only succeed
in this broader context. For now, we need to be aware that online, the
climate change ``debate'' may not be a debate at all.

\section*{Acknowledgments}
This study and the associated research were conducted within the
framework of the \href{http://climatoscope.org}{Climatoscope} and
\href{http://politoscope.org}{Politoscope} platforms of the Paris
Ile-de-France Institute of Complex Systems. 
They were also supported by the European project NODES
(LC-01967516-CNECT/2022/5162608), the Ile-de-France Region, the City of
Paris and, via a PhD grant, by the CFM Foundation for Research.

\CDRGrant[EC]{LC-01967516-CNECT/2022/5162608}

\section*{Declaration of interests}
The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Supplementary materials}
Supporting information for this article is available in open access in
the Harvard Dataverse repository, at
\url{https://doi.org/10.7910/DVN/QIC8SB}.

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crgeos-304-suppl.pdf}}

\back{}

\printbibliography
\refinput{crgeos20240760-reference.tex}

\end{document}
