Protesters linked hands near the violent heart of the Paris terror attacks Sunday, giving an emotional jolt to world leaders flying into the French capital to try and save Earth from climate catastrophe.
As hundreds of thousands of people joined protests worldwide, the human chain aimed to send a highly symbolic message to leaders on the eve of the official opening of a 195-nation UN climate summit in Paris.
French authorities cancelled two climate demonstrations in the City of Light after gunmen and suicide bombers killed 130 people on November 13.
Instead of marching, activists left thousands of pairs of shoes -- weighing more than four tonnes according to organisers -- on Place de la Republique square. A pair of running shoes was left by UN Secretary General Ban Ki-Moon, and Pope Francis sent shoes to be placed on his behalf.
In the first organised demonstration in the French capital since the attacks, climate protesters of all ages lined the wind-blown streets to link up in a two-kilometre (1.2-mile) human chain.
"Hear our voices! We are here!" they changed, and held up placards with messages such as: "For a climate of peace".
"There was a lot of solemnity, dignity on the pavements. there was a powerful current that passed between people's hands," said Genevieve Azam, spokeswoman for organising group Attac.
"It was a pleasure to be able to lift the lid that has weighed on French people since the attacks."
Protesters left a 100-metre (300-foot) gap in the chain where flowers have been left outside the Bataclan concert hall, where the worst violence claimed 90 lives, as a mark of respect to the victims.
- Superstorms, drought -
Some 150 leaders including US President Barack Obama, China's Xi Jinping, India's Narendra Modi and Russia's Vladimir Putin will attend the official start Monday of the UN conference tasked with reaching the first truly universal climate pact.
About 2,800 police and soldiers will secure the conference site, and 6,300 others will deploy in Paris.
French Interior Minister Bernard Cazeneuve said nearly 1,000 people thought to pose security risks had been denied entry into France.
The goal of the climate talks is to limit average global warming to no more than two degrees Celsius (3.6 degrees Fahrenheit), over pre-Industrial Revolution levels by curbing fossil fuel emissions blamed for climate change.
"I hope this time the conference will lead to something solid," said protester Denis Diderot, a retired university teacher who joined the demonstration wearing a beret.
Rallies demanding curbs on carbon pollution have been growing around the world since Friday, with marches involving tens of thousands across Australia Sunday kickstarting a final day of people-powered protest.
Similar events were planned for Rio de Janeiro, New York and Mexico City, with protesters echoing scientific warnings of superstorms, drought and rising sea levels swamping vast areas if concrete action is not taken soon.
In Madrid, about 10,000 people, many of htem waving placards reading "Stop CO2", marched on the main Puerta del Sol square, led by a group of children.
- 'Mum, did you know?' -
"In 10 years' time our children are going to say, 'Mum, did you know about this? What was everyone doing'?" said Kate Charlesworth, a doctor and mother in Sydney, where 45,000 people converged.
Religious leaders in Paris delivered petitions to the UN summit organisers with almost 1.8 million signatures demanding immediate climate action.
In a sign of the urgency, the start of the negotiations themselves, conducted by bureaucrats, have been brought forward to Sunday -- the eve of the official opening.
In the past week, the UN's weather body said the average global temperature for the year 2015 is set to rise one degree Celsius above pre-industrial levels, halfway towards the targeted UN ceiling.
Voluntary carbon-curbing pledges submitted by nations to bolster the Paris pact, even if fully adhered to, put Earth on track for warming of 2.7-3.5 degrees C, according to UN climate chief Christiana Figueres.
French President Francois Hollande, host of the November 30-December 11 talks, has warned of obstacles ahead for the 195 negotiating nations.
Potential stumbling blocks range from finance for climate vulnerable and poor countries to scrutiny of commitments to curb greenhouse gases and even the legal status of the accord.
The last attempt to forge a global deal -- the ill-tempered 2009 Copenhagen summit -- foundered upon divisions between rich and poor countries.