Michael Knowles, who hosts a podcast for Ben Shapiro's right-wing website the Daily Wire, argued the new wave of climate activism inspired by figures including Ms Thunberg, 16, was “hysteria” and that the teenager was “being exploited by her parents and by the international left”.
Ms Thunberg, who began protesting the political response to climate change when she was 15 by taking time off school to demonstrate outside the Swedish parliament, was diagnosed with Asperger’s – a form of autism – in 2015.
Speaking on Fox’s The Story programme, Knowles said: “The climate hysteria movement is not about science. If it were about science it would be led by scientists, not politicians and a mentally ill Swedish child who is being exploited by her parents and by the international left.”
When challenged by left-wing pundit Chris Hahn, Mr Knowles reiterated that she “has many mental illnesses”.
His comments came after the teenager gave a severe and impassioned speech to the United Nations climate change summit, telling world leaders and officials from about 60 countries “I shouldn’t be up here. I should be back in school on the other side of the ocean. Yet, you all come to us young people for hope? How dare you. You have stolen my dreams and my childhood with your empty words.”
Fox News has since apologised to the 16-year-old for the conservative podcast host’s comments, adding they have “no plans” to feature Mr Knowles on the channel in the future.
A spokesperson told the Hollywood Reporter: “The comment made by Michael Knowles who was a guest on The Story tonight was disgraceful — we apologise to Greta Thunberg and to our viewers."
The pundit’s comment drew criticism for groups who speak out for people living with autistic spectrum disorder. Julia Bascom, executive director of the Autistic Self Advocacy Network, said “It's absolutely unconscionable to attack someone for their disability, especially when that person is a child.
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“History is full of autistic people and people with other cognitive disabilities who were and are compelling, credible activists and leaders. Greta is a part of that tradition, and our community is lucky to have her. Period."
Ms Thunberg has faced repeated criticism and comments on her condition, particularly from climate change sceptics, after issuing blunt warnings to world leaders about the state of the planet, but has described her Asperger’s as a “superpower”.
“When haters go after your looks and differences, it means they have nowhere left to go”, she wrote on Twitter in August. “I'm not public about my diagnosis to ‘hide’ behind it, but because I know many ignorant people still see it as an 'illness', or something negative. And believe me, my diagnosis has limited me before.
“Before I started school striking I had no energy, no friends and I didn’t speak to anyone. I just sat alone at home, with an eating disorder. All of that is gone now, since I have found a meaning, in a world that sometimes seems shallow and meaningless to so many people.”
The activist has also repeatedly faced claims that she has been indoctrinated by her opera singer mother and actor father, although her parents insist that it was her who convinced them of the urgent need to address climate change.
In an interview with the Guardian in July, her father Svante Thunberg said “She kept showing us documentaries, and we read books together. Before that, I really didn’t have a clue. I thought we had the climate issue sorted.”