Extinction Rebellion (XR) has announced it will blockade Parliament until the Government debates its three demands.
The environment activists plan to set up blockades in Westminster to prevent ministers from getting to work when Parliament returns from its summer recess in September.
"We’re not going to let them back in until they agree to start anew with justice, care and life at the heart of it," said the campaigners in a statement on their website.
Similar protests are planned for Cardiff and Scotland and as a precursor to the main demonstrations in September, XR will start a countdown to rebellion from August 28 with local groups invited to cause "high impact disruption" in their areas.
XR's three demands on the Government are that it declares a climate and ecological emergency, it commits to reducing greenhouse gas emissions to net zero by 2025 and for the Government to form a Citizens' Assembly on climate and ecological justice.
Clare Farrell, XR co-founder, said if business continued as normal the world was guaranteed "mass death and eventual extinction".
"With this prognosis in mind, empathy, compassion and solidarity are a pragmatic necessity, and they are vital ingredients of our rebellion," said Ms Farrell.
“Extinction Rebellion recognises that the climate crisis is a symptom of a far wider kind of malaise and corruption in our politics, society and the human imagination.
"In the failed story of unlimited growth and spiralling inequality we are told to forget about our power, our community, and our rights as citizens. But together we are powerful.
“It’s time we start a new story. One of compassion, community and trust. One where we reclaim the words 'growth' and 'value' and give them new meaning."
They also referenced a Climate Change Committee report which warns of a future world that is four degrees warmer.
Alex Armitage, Pediatrician and a member of Doctors for XR, added: “The Lockdown was an opportunity to confront the huge challenges of climate change but the Government, addicted to the malignant ideology of unlimited economic growth, is now pushing us in the opposite direction.
“We have lobbied MPs, stood for election, written letters, emails and we have tweeted at powerful people.
"But one thing gets clearer and clearer, our political system is rotten, no longer serving the needs of ordinary people."
Boris Johnson was asked for his thoughts about XR's plans for mass demonstrations in September in an interview with LBC's Nick Ferrari this morning.
The Prime Minister said: “I think they should be supporting the incredible things this Government is doing to combat climate change and if I were Extinction Rebellion I would be jumping for joy.
“Look at our plans for a green recovery, look at the amazing things we’re going to do to get this country making wind turbines, making batteries, the ambition I announced for a ‘jet zero’ – to be the first country to produce a zero-emission long-haul passenger jet.
“I mean, Extinction Rebellion should look at some of the things this Government is doing to tackle climate change and support us.”