The United Nations human rights chief has condemned “verbal attacks” on teenage environmental activist Greta Thunberg after calling on government to take the threat posed by climate change more seriously.

Michelle Bachelet, the UN High Commissioner for Human Rights, warned on Monday during her address to the Human Rights Council that climate change has become an unprecedented threat to freedoms worldwide.

“The world has never seen a threat to human rights of this scope,” Ms Bachelet said. “This is not a situation where any country, any institution, any policymaker can stand on the sidelines.

“We are burning up our future – literally.”

Ms Bachelet then turned to criticism of environmental activists, decrying ”verbal attacks on young activists such as Greta Thunberg and others.”

Greta Thunberg inspires climate activists everywhere: In pictures Show all 12 1 /12 Greta Thunberg inspires climate activists everywhere: In pictures Greta Thunberg inspires climate activists everywhere: In pictures In the protest that started a movement, Greta skips school to sit outside of the Swedish parliament in Stockholm in order to raise awareness of climate change on 28 August 2018 Getty Greta Thunberg inspires climate activists everywhere: In pictures Greta speaks at the World Economic Forum in Davos on 25 January AFP/Getty Greta Thunberg inspires climate activists everywhere: In pictures Greta stages a protest at the World Economic Forum in Davos on 25 January Reuters Greta Thunberg inspires climate activists everywhere: In pictures Greta speaks at the House of Commons in London on 23 April PA Greta Thunberg inspires climate activists everywhere: In pictures Greta addresses to the occupation at Marble Arch in London on 21 April AFP/Getty Greta Thunberg inspires climate activists everywhere: In pictures Greta meets the pope on a visit to Rome Reuters Greta Thunberg inspires climate activists everywhere: In pictures Greta speaks at the senate in Rome on 18 April Reuters Greta Thunberg inspires climate activists everywhere: In pictures Greta addresses a debate of the EU Environment, Public Health and Food Safety committee at the European Parliament in Strasbourg on 16 April AFP/Getty Greta Thunberg inspires climate activists everywhere: In pictures Greta receives the Special Climate Protection Award at the German Film and Television awards in Berlin on 30 March AFP/Getty Greta Thunberg inspires climate activists everywhere: In pictures Greta attends a children's climate protest in Berlin on 29 March AFP/Getty Greta Thunberg inspires climate activists everywhere: In pictures Greta addresses a children's climate protest on 1 March in Hamburg Getty Greta Thunberg inspires climate activists everywhere: In pictures Greta attends a meeting for the Civil Society For rEUnaissance at the EU Charlemagne Building in Brussels on 21 February AFP/Getty

Swedish teenager Ms Thunberg has become the poster girl of a renewed wave of youth environmental activism worldwide, after she sparked the ‘climate school strikes’ movement earlier this year.

But as she has grown in fame – amassing 1.4 million followers to date on Twitter – so the backlash from some public figures has grown more vicious.

During her recent voyage by yacht to New York to attend a UN Climate Action Summit set to begin on 23 September, the Brexit-backing businessman Arron Banks tweeted: “Freak yachting accidents do happen in August ...”.

Ahead of a speech to the French parliament in July, one of several sermons she has given to political leaders, some far-right and conservative MPs staged a boycott and hurled insults, calling her the “Justin Bieber of ecology” and a “prophetess in shorts”.

Ms Thunberg, who has Aspergers, has also fought back. Last month when a newspaper columnist called her “deeply disturbed”, she responded by asking: “Where are the adults?”.

In her speech, Ms Bachelet also joined the global outcry in recent weeks over far-right Brazilian president Jair Bolsonaro for his handling of fires that continue to ravage the Amazon rainforest.

Michelle Bachelet, the UN High Commissioner for Human Rights, hit out at critics of Greta Thunberg in a bold speech (REUTERS)

“The fires currently raging across the rainforest may have catastrophic impact on humanity as a whole,” Ms Bachelet said, “but their worst effects are suffered by the women, men and children who live in these areas, among them, many indigenous peoples.”

Ms Bachelet, a former president of Chile, urged authorities in Brazil, as well as Paraguay and Bolivia, to ensure “longstanding environmental policies” are carried out, “thus preventing future tragedies.”

She also spoke of her “alarm” at migrant children still being held in detention centres in the United States and Mexico, expressing concern that policies by the United States, Mexico and others in the region “are putting migrants at heightened risk of human rights violations and abuses.”

The Trump administration pulled the United States out of the council last year, accusing it of an anti-Israel bias and denouncing some member states that Washington says are repeat rights violators.