Germany’s rightwing populists are embracing climate change denial as the latest topic with which to boost their electoral support, teaming up with scientists who claim hysteria is driving the global warming debate and ridiculing the Swedish climate activist Greta Thunberg as “mentally challenged” and a fraud.

The Alternative für Deutschland party (AfD) is expected to launch its biggest attack yet on mainstream climate science at a symposium in parliament on Tuesday supported by a prominent climate change denial body linked by researchers to prominent conservative groups in the US.

The AfD’s focus on climate change has increased since it entered the Bundestag in autumn 2017. It has added a sceptical voice to the rising number of parliamentary debates on the topic and concentrated its opposition specifically on the scandal over diesel car emissions and plans to phase out brown coal.

But the attention the party paid to the topic has been noticeably ramped up since the emergence last August of Greta, the teenage climate activist who has appeared at climate rallies across Europe, including in Germany.

A joint investigation by Greenpeace Unearthed and the counter-extremism organisation the Institute for Strategic Dialogue (ISD) has shown a surge in AfD digital communication on climate issues. While climate change barely got a mention on its social media channels when the AfD was first founded in 2013, it mentioned the topic on its channels about 300 times in 2017-18, and that has tripled over the past year to more than 900, with its main focus on Greta.

Play Video 2:04 The Greta Thunberg effect: her activism in London in two minutes - video

The party, whose members have been seen handing out climate change denial leaflets at school climate strikes, has ratcheted up its anti-Thunberg rhetoric ahead of the EU parliamentary elections this month. Its candidates have made comparisons between the Swedish teenager and a member of a Nazi youth organisation and called for her to seek treatment for what Maximilian Krah, an AfD candidate for the EU elections, called her “psychosis”.

It has also been repeatedly claimed on AfD’s Facebook page that she is the leader of a climate movement cult. Posts on the page make repeated use of terms such as “CO2Kult” (CO2 cult), “Klimawandelpanik” (climate change panic) and “Klimagehirnwäsche” (climate brain washing).

US is hotbed of climate change denial, major global survey finds Read more

Jakob Guhl, an ISD researcher, said climate change denial had become key to the party’s political platform. “The AfD has been denying human-made climate change on its social media pages since 2016, and while it has not shifted its position it is clear that the party decided to communicate it more frequently.

“The fact that many mainstream politicians from across the political divide in Germany supported a 16-year-old female activist who was virtually unknown until a few months ago, allowed the party to present belief in climate change as irrational, hysteria, panic, cult-like or even as a replacement religion. Attacking Greta, at times in fairly vicious ways, including mocking her for her autism, became a way to portray the AfD’s political opponents as irrational.”

The party’s symposium at the Bundestag is backed by the European Institute of Climate and Energy (EIKE), a group that rejects mainstream scientific consensus that climate change is man-made and has links to prominent conservative groups in the US.

EIKE’s annual climate conference is co-sponsored by the Heartland Institute, a fossil fuel industry-funded US thinktank that has a history of funding projects aimed at weakening public confidence in climate science, the investigation found. EIKE’s president, Holger Thuss, co-founded the European branch of another US climate change denial pressure group, Committee for a Constructive Tomorrow (CFACT).

Profile Who is Greta Thunberg? Show Hide 'Never too small to make a difference' In August 2018 Thunberg began a solo climate protest by striking from school in Sweden when aged 15. She has since been joined by tens of thousands of school and university students in Australia, Belgium, Germany, the United States, Japan and more than a dozen other countries. 'Irresponsible children' Speaking at the United Nations climate conference in December 2018, she berated world leaders for behaving like irresponsible children. And in January 2019 she rounded on the global business elite in Davos: “Some people, some companies, some decision-makers in particular, have known exactly what priceless values they have been sacrificing to continue making unimaginable amounts of money. And I think many of you here today belong to that group of people.” Inspiration Veteran climate campaigners are astonished by what has been achieved in such a short time. Thunberg has described the rapid spread of school strikes for climate around the world as amazing. “It proves you are never too small to make a difference,” she said. Her protests were inspired by US students who staged walk-outs to demand better gun controls in the wake of multiple school shootings. Family Her mother, Malena Ernman, has given up her international career as an opera singer because of the climate effects of aviation. Her father is actor Svante Thunber. Greta has Asperger’s syndrome, which in the past has affected her health, he says. She sees her condition not as a disability but as a gift which has helped open her eyes to the climate crisis. Photograph: Michael Campanella/CampanellaFoto

CFACT Europe received financial support from its US counterpart, according to documents seen by the Guardian.

Thuss acknowledged to Greenpeace Unearthed that he was “one of Heartland’s many experts”, and did not deny financial links between Heartland and EIKE but was keen to stress he was a member of Angela Merkel’s Christian Democrats and not the AfD.

He told Greenpeace Unearthed that CFACT Europe had been disbanded, although he did not say when, and denied that EIKE was supporting the AfD’s symposium, despite it promoting it on the homepage of its website as as an opportunity to “set facts against CO2 hysteria and climate activism”.

EIKE’s vice-president, Michael Limburg, who has previously run as a candidate for the AfD, has insisted EIKE was not politically affiliated, but admitted “loose ties” between EIKE, Heartlands and CFACT.

Among the scheduled speakers at the AfD event are the Tirolean glaciologist Gernot Patzelt, the Danish atmospheric physicist Henrik Svensmark, and Christopher Monckton, 3rd Viscount Monckton of Brenchley, a former Ukip candidate described as a hereditary peer, hobby mathematician and former adviser to Margaret Thatcher, who claims models used to measure climate change are flawed.

Facebook Twitter Pinterest The former Ukip candidate Christopher Monckton is speaking at the AfD climate denial event. Photograph: Alan Porritt/EPA

Promotional materials for the event cite Greta as someone placed on the frontline of climate activism “by PR professionals seeking to bedevil the plant-nutrient carbon dioxide” and describe the AfD as “the only party in Germany not willing to back the supposed climate consensus”.

The AfD did not respond to requests for comment.

Karsten Smid, a climate campaigner for Greenpeace Germany, told the Guardian: “The AfD is using the Bundestag as a stage for its dissemination of climate lies. They invite fake experts to a so-called symposium on climate change to generate content for mass dissemination via social media channels and stir up hatred and anger on the internet.

“We are experiencing a shift to the right on social media and in society. In a short period of time, the new right has established its own counter-society on climate issues. With troll armies, agitating magazines and the support of climate sceptics like EIKE, it has created its own sphere that is massively underestimated.”