Young ecologist Greta Thunberg addresses French parliament

Swedish teenage climate activist Greta Thunberg hit back at critics as she visited the French parliament on Tuesday following outraged comments from some right-wing MPs who have slammed her presence.

"Some people have chosen not to come here today, some have chosen not to listen to us. And that is fine. We are, after all, just children," said Thunberg.

"You don't have to listen to us. But you do have to listen to the science ... and that is all we ask, to unite behind the science."

Thunberg, whose school strikes protesting government inaction over climate change helped spark a worldwide movement, spoke to MPs at the National Assembly (lower house) and then attended debates in the main chamber as a guest of honour.

"We become the bad guys who have to tell people these uncomfortable things because no one else wants to, or dares to," said Thunberg, speaking in English at one of the parliament's conference rooms.

"And just for quoting or acting on these numbers, these scientific facts, we receive unimaginable amounts of hate and threats. We are being mocked and lied about by members of parliament and journalists," she added.

The activist, who was invited by 162 MPs from a cross-party group concerned about climate change called "Let's Accelerate", was welcomed by speaker Richard Ferrand at his residence before heading to parliament.

Divided French political class

Many conservative figures on the French right criticised the invitation for her to speak, dismissing her as the "Justin Bieber of ecology".

Republicans MP Guillaume Larrive called on MPs to boycott her appearance, saying that to fight climate change "what we need is scientific progress and political courage, not apocalyptic gurus".

Julien Aubert, like Larrive a Republicans MP contending for leadership of the right-wing party, snapped: "Don't count on me to applaud a prophetess in shorts, a Nobel Prize for Fear."

Jordan Bardella, an MEP who is one of the rising stars of the far-right National Rally (formerly the National Front), told France 2 television derided the "dictatorship" of emotion when it relies on "children".

Bardella, 23, lashed out at the use of "children to exhibit a fatalism to try to explain to all young people that the world is finished, that everything is going to catch fire and that nothing is possible".

Thunberg, who on her Twitter feed describes herself as a "16 year old climate activist with Asperger", has long been the target of vicious attacks by social media trolls. But it is rare for politicians to join the fray.

"It is sad people are so desperate that they make things up," she told French youth news site Konbini ahead of her visit to parliament.

"It seems they are more scared and concerned about me and some young people protesting than the actual problem."

Her appearance comes as France again swelters in a new heatwave with record-high temperatures expected in Paris on Thursday.