People participate in a rally during a global day of action on climate change in Sydney on November 6, 2021, as world leaders attend the COP26 UN Climate Change Conference in Glasgow. AFP
From Paris to Sydney, Nairobi to Seoul, more than 200 events are planned worldwide to demand immediate action for communities already affected by climate change, particularly in the poorer countries in the South.
In Glasgow, organisers and police said they expected up to 50,000 people to parade through the streets of the Scottish city near the COP26 summit venue, which is under tight security.
Delegates from nearly 200 countries are in Glasgow to hammer out how to meet the Paris Agreement goals of limiting temperature rises to between 1.5 and 2 degrees Celsius.
At the halfway stage of the COP26 negotiations, some countries have signed up to pledges to reduce their greenhouse gas emissions, with separate deals on phasing out coal, ending foreign fossil fuel funding and slashing methane.
The promises followed a major assessment that showed global CO2 emissions were set to rebound in 2021 to pre-pandemic levels.
But activists have been left unimpressed by the summit so far.
"They cannot ignore the scientific consensus and they cannot ignore us," said Thunberg.
"This is no longer a climate conference. This is now a global greenwashing festival."
In Australia on Saturday, protesters in Sydney and Melbourne -- some dressed as lumps of coal or Prime Minister Scott Morrison, a vigorous defender of the mining industry -- labelled the talks "a sham" and their national leader "an absolute embarrassment".
"No more blah, blah blah. Real climate action now," read one sign at a protest in Sydney.
The South Korean capital of Seoul saw around 500 take to the streets demanding immediate action for communities already hit by the fallout of a heating planet.
South Korea has few energy resources of its own and relies on imported coal -- a cheap but dirty fuel -- for around 40 percent of the electricity powering the world's 12th-largest economy, according to figures from the International Energy Agency.
The country aims to be carbon neutral by 2050, but local activists say the goal cannot be accomplished without more fundamental changes.
"At COP26, the expected 'blah blah blah' is taking place," Climate Strike, one of the organising groups of Saturday's march in Seoul, said.
Security has been boosted around Glasgow's locked-down city centre ahead of the planned demonstrations there, which are expected to draw a variety of groups including Extinction Rebellion.
"Many thousands of us are marching right across the world today to demand immediate and serious action," said Scottish activist Mikaela Loach.
"We're clear that warm words are not good enough -- and that the next week of talks must see a serious ramping up of concrete plans."
'Can't go on today'
COP26 negotiations will continue on Saturday before taking a pause on Sunday ahead of what is shaping up to be a frantic week of shuttle diplomacy, as ministers arrive to push through hard-fought compromises on a number of issues.
Countries still need to flesh out how pledges made in the Paris deal work in practice, including rules governing carbon markets, common reporting timeframes and transparency.
Countries came into COP26 with national climate plans that, when brought together, put Earth on course to warm 2.7C this century, according to the UN.
With just 1.1C of warming so far, communities across the world are already facing ever more intense fire and drought, displacement and economic ruin wrought by global heating.
Brianna Fruean, a Samoan member of the Pacific Climate Warriors, who addressed a world leaders' summit at the start of COP26, said it was time for leaders to take note of protesters' demands.
"It can't go on like this," she said.
"We refuse to be just victims to this crisis. We are not drowning, we are fighting and on Saturday the world will hear us."