Greta Thunberg, the 16-year-old Swedish environmental activist, has given her support for a general strike for the climate, saying the student movement she inspired needs more support from older generations to ensure politicians keep their promises under the Paris agreement.

Speaking at a public event in London as Extinction Rebellion protests continued in the capital, the initiator of the school strike for climate movement was typically frank about the scale of the problem the world faces and the impact her campaign has made. “People are slowly becoming more aware, but emissions continue to rise. We can’t focus on small things. Basically, nothing has changed,” she said.

At several points, she stressed the need for the protests to spread. “This is not just young people being sick of politicians. It’s an existential crisis,” Thunberg said. “It is something that will affect the future of our civilisation. It’s not just a movement. It’s a crisis and we must take action accordingly.”

In a question and answer session, Franny Armstrong, the director of the climate documentary The Age of Stupid, asked whether it was time for a general strike. “Yes,” replied Thunberg in unison with the other members of the panel.

Traditional unions have so far been wary of joining the strikes. Although workers’ federations in Italy made Thunberg an honorary member, most others have given either tepid support or none due to concerns about the possible impact on jobs. But there is growing support in the UK, the US and other countries for a Green New Deal that would increase spending on renewable energy.

The talk took place on Earth Day, after a week of protests by Extinction Rebellion activists pushed the climate crisis on to news broadcasts and newspaper front pages.

Police have arrested more than 1,000 demonstrators at Parliament Square, Oxford Circus and Waterloo Bridge, but hundreds remain camped in Marble Arch, where Thunberg spoke on Sunday.

“I support Extinction Rebellion. What they are doing is good. Civil disobedience is important to show this is an emergency. We need to do everything we can to put pressure on the people in power,” she told the audience on Monday, prompting cheers and applause.

“Why study for a future that is being taken from us? Why study for facts when facts don’t matter in this society? It’s empowering to know I am doing something, I am taking a stand, I am disrupting.”

The interest in the event was so intense that a long line of supporters stretched along Euston Road waiting for the doors to open at Friends House. Most guests appeared to be fellow school strikers. A handful wore shirts or headbands printed with the Extinction Rebellion symbol.

Facebook Twitter Pinterest An Extinction Rebellion activist sits in front of tents at Marble Arch in London. Photograph: Tolga Akmen/AFP/Getty Images

But the audience included all age groups, and just about every major environment organisation associated itself with the talk, which was hosted by the Quakers and co-organised by Guardian Events. When Thunberg appeared on stage, she was greeted with thunderous applause.

Armstrong said: “I’ve been to dozens of talks here over the years, but I’ve never seen anything like this. It’s the first time I have seen a standing ovation even before the event starts. She’s a rock star.”

In the past week, Thunberg has met Pope Francis in the Vatican and addressed members of the European parliament. On Tuesday, she will visit the Houses of Parliament, meet the House of Commons Speaker, John Bercow, and take part in an event with the leaders of all the main parties except Theresa May.

Play Video 1:14:13 Greta Thunberg, Anna Taylor and Caroline Lucas on the new climate movement | Guardian Live

She told the audience she had been taken by surprise at the swift spread of a movement that began less than a year ago, when she went on strike alone outside the Swedish parliament. “It is hard to understand what is happening during the last months. It has all happened so fast. I don’t have time to think it through,” she said.

Veteran observers of the British parliament said she has helped push the climate issue higher up the UK political agenda than at any time since the 2008 Climate Change Act.

Green party officials said they hoped the meeting on Tuesday could spur a new phase of cross-party collaboration on climate change, including monthly meetings, wider public consultations and an agreement that party manifestos should be vetted by an independent body such as the Committee on Climate Change to assess whether they are in line with the Paris agreement.

Facebook Twitter Pinterest People queue outside Friends House in London to hear Thunberg speak. Photograph: Jill Mead/The Guardian

Caroline Lucas, the Green party MP, said the current wave of climate action on the streets and the school strikes gave her hope. “There is more political leadership there and here than I have seen in Westminster. It feels like a turning point in the history of how we defend our planet,” she said.

“Young people are calling out against a system that is sadly broken … We are going to change the definition of what is politically possible so that it is what is scientifically necessary.”

The discussion ranged from veganism and avoiding flying to political change throughout society. Thunberg said everything was necessary, though she put the focus on challenging the companies and governments that are responsible for the bulk of emissions.

How to deal with with people in power was a frequent subject of questions to the panel. Thunberg said her autism helped her filter out much of the greenwashing.

Facebook Twitter Pinterest The panel at the event also included the Green party MP, Caroline Lucas, right. Photograph: Jill Mead/The Guardian

“We are more likely to see through lies. We don’t follow the stream. You can’t be a little bit sustainable – either you are sustainable or you are not,” she said.

There were occasional moments of levity. At one point, Thunberg was asked how she dealt with climate deniers. “I don’t,” she replied.

Thunberg’s earlier point was reiterated by Anna Taylor from the UK Student Climate Network. “We are not going to be satisfied by politicians saying ‘we support you’ and then walking away,” she said.

“We won’t be satisfied until they meet our demands and act. That’s why simply taking a selfie or posting support on Twitter isn’t enough. That’s why we have to keep striking.”

Extinction Rebellion protest day eight – in pictures Read more

For all the talk of politics and protest, however, some of the most poignant and pertinent questions came from the youngest children. One asked: “If pollution continues, how much time have we got left?” Another wanted to know: “Can we achieve our goal in the time we have?”

Thunberg, in response, was reassuring but measured: “Of course we can, it’s physically possible, the scientists say. It’s up to us. If we do this now then of course we will. But if we don’t, we might not do it. But yes, definitely we can.”