Paris climate change talks: Worldwide protests as leaders prepare for start of COP21 summit

Thousands of demonstrators across the world from Sydney to London have staged one of the largest ever days of protest

Policemen fight with climate change activists at the Place de la Republique in Paris (AP)

Placards warning the world’s leaders that there is “No Planet B” were waved. People dressed as polar bears or angels to demand “climate justice”. And the Pope, among others, sent a pair of his shoes to symbolise the marchers forced from the streets of Paris by terror.

Thousands of demonstrators across the world from Sydney to London have staged one of the largest ever days of protest to halt climate change ahead of the start of the United Nations summit in the French capital to thrash out a legally-binding agreement to curb emissions.

The gathering to be attended by 150 heads of government, including Prime Minister David Cameron and US President Barack Obama, is seen by many as the last opportunity to strike a global deal that would bring within sight the UN’s long-term goal of limiting global warming to 2C.

More than 2,500 demonstrations were held around the world, including a march by 45,000 people in Sydney hailed as the largest of its kind ever held in Australia. Organisers of a demonstration in London claimed it was attended by 50,000 and declared it “the biggest climate march in British history”.

In Paris, where the authorities had banned a planned march on public safety grounds following the 13 November atrocities, protesters laid out hundreds of pairs of shoes in the Place de la Republique to represent the missing demonstrators.

Among the symbolic ranks of high heels and sandals on the square that has been a gathering point for Parisians since the terror attacks was a pair of creased black shoes sent by Pope Francis, a vocal campaigner for action to prevent dangerous climate change. UN Secretary General Ban Ki-Moon provided a pair of jogging shoes.

Elsewhere in the French capital, some 10,000 joined arms to form a human chain along the route of the planned march.

The call for peaceful demonstration from organisers was defied by a small group who clashed with riot officers near the Place de la Republique. Police, who responded to the violence with tear gas, said they had arrested 100 people in connection with the clashes.

Campaigners warned that failure to reach an agreement that locks in action to slash carbon emissions would mean that the last opportunity to prevent the most extreme consequences of global warming had been lost.

The warnings were backed by Labour leader Jeremy Corbyn as he addressed marchers in London’s Hyde Park, where campaigners were joined by actor Emma Thompson and fashion designer Vivienne Westwood.

Addressing leaders attending the summit, Mr Corbyn said: “Do what you are sent there to do. Do what you have been sent there on our behalf [to do].”

The main challenge in Paris is to agree a process - known as a “ratchet mechanism” - that would require countries to step up their pledges to cut emissions every few years until they are sufficient to limit global warming to 2C.

Developing countries have warned that even at 2C, global warming will cause huge problems.