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.