After a pandemic hiatus, Extinction Rebellion plans to resume large-scale street protests next week in a bid to push for more rapid action on increasingly evident climate threats.
With heat records broken, and wildfires, hurricanes and floods wreaking havoc from India to the United States, "we know humanity itself is at very, very grave risk," said Clare Farrell, a co-founder of the climate activist group.
But huge behavioural changes in response to the COVID-19 pandemic - and trillions of dollars in government spending in response - also indicate the viability of fast and large-scale action on serious global threats, she said.
"It's shown us things can change very rapidly when people realise there is an existential threat to human life," she said in an online briefing on Thursday.
Activists said a series of smaller regional protests - many around airports, an important source of planet-heating emissions - will kick off this Friday in Britain, followed by marches in London, Manchester and Cardiff starting next Tuesday.
The protests are expected to draw fewer participants than previous actions, as organisers try to adhere to government social distancing guidelines.
"Obviously we're expecting lower numbers than in October because of COVID and because we're encouraging social distancing," said Anneka Sutcliffe, a protest organiser, referring to the group's last major protests.
She said she expected "thousands" of activists to take part.
Planned action in May was cancelled amid the virus outbreak. But an easing of restrictions - schools, restaurants and offices are re-opening - has created space to resume, she said.
Paul Stephens, a police liaison for Extinction Rebellion, said restrictions on gatherings of 30 or more people mean the group risks heavy fines - though it says demonstrations should be exempt.
Extinction Rebellion organisers said a UK citizen's assembly called early this year to advise on how to meet Britain's 2050 net-zero emissions goal had been a positive step in involving people in decision-making on climate change.
The group, reflecting the country's demographic diversity, is set to deliver recommendations to government next month.
But activists said it fell short as participants could not question whether the 2050 goal was sufficiently ambitious.
Extinction Rebellion activists say an emergency response and mass move away from polluting industries and behaviours is needed to avert a looming climate cataclysm.
Chidi Obihara, a finance expert with the group, took aim at British government stimulus spending, saying cash to airlines and other polluters had not mandated a cut in emissions, as in other countries.
Extinction Rebellion organisers said the group - criticised for its largely white, middle-class support - had spent time in lockdown building ties with other activist movements.
With a new global push for racial justice under the 'Black Lives Matter' banner, climate activists are now "joining this much bigger story of rebellion against this toxic system", said Alejandra Piazzolla, an activist originally from Colombia.
Climate activists have supported racial justice protests in recent months, she said, and while Extinction Rebellion "has faced a lot of challenges about how they relate to other communities .... we're all learning and growing".