Half of people regularly tweeting about the climate and nature crises abandoned Twitter after it was taken over by Elon Musk, according to new analysis.

The researchers said Twitter, now renamed X, had previously been the leading social media platform for environmental discussion and the decline was “troubling”. They said the “exodus of environmental users on Twitter is an existential threat” to a main way of informing people who want to take climate action.

Musk, who has called himself a “free speech absolutist”, radically cut Twitter’s content moderation staff after the takeover, which began in April 2022 and was finalised in October 2022.

Reports have found rising climate change dis- and misinformation on the platform and a dramatic increase in hate speech. Scientists and others told the Guardian in December that there had been a surge in debunked climate change denialist talking points on Twitter since the Musk takeover.

The researchers studied 380,000 users who tweeted regularly about global heating and biodiversity and found that 47.5% had become inactive six months after the final takeover. By comparison, only 21% of a control group of 458,000 who tweeted about US politics became inactive in the same period.

“The incredible power of Twitter was that it was this open forum where people could share ideas and opinions and influence other people,” said Prof Charlotte Chang, of Pomona College in the US, who led the research. “We have this immense challenge of empowering stakeholders across all sectors of society to take action to halt the loss of biodiversity and to combat catastrophic climate change. We were pretty disheartened to find that after the sale, our environmental Twitter community has really declined.”

The analysis, titled: Environmental users abandoned Twitter after Musk takeover, is published in the journal Trends in Ecology & Evolution. It analysed the Twitter use of the groups in 15-day intervals from July 2019 to April 2023. A user was deemed to be active if they tweeted at least once about their topic in a 15-day window.

Chang said it was uncertain where the environmental discourse now missing from Twitter might be moving to, with Mastodon, Threads and Instagram yet to replicate the past success of Twitter in this area. She said the decline on Twitter could well continue, with previous research on social networks noting a snowball effect where users leaving leads to others following.

“This snowball may have been kicked off too much to really halt the ongoing trend,” Chang said. The researchers highlighted initiatives such as the Coalition for Independent Technology Research as a way of raising coordinated concerns to Twitter and policymakers. X’s media office did not respond to a Guardian request for comment.

Chang said plans to start charging significant sums for access to large numbers of tweets via the platform’s API would damage research. “It would make it impossible to access and understand what’s happening on these platforms, to document their positive contributions to society as well as some of the harms,” she said.

Leo Hickman, editor of Carbon Brief, said: “Over the past decade, Twitter has been the best social-media platform by far for following, sharing and discussing the latest news and talking points about climate change. In particular, many climate scientists have found a place to explain their work and findings in detail. But this study’s results only confirm the lived experience about just how toxic and alienating Twitter has become for people hoping to converse about the challenges of climate change in a nuanced, sensible way.”

In May, the climate scientist Prof Mark Maslin, of University College London, said: “There’s been a massive change. I get so much abuse and rude comments now.” Maslin said he used to have regular meetings with Sean Boyle, Twitter’s former head of sustainability. “But he was sacked [in Musk’s mass cull of staff] and Twitter became the wild west.”