Organisers claimed 500,000 people turned out for the march, but authorities in Madrid put the number at 15,000 without an immediate explanation for the disparity in the count. Thunberg addresses a demonstration in Madrid. Her placard translates as "Strike for Climate". Credit:AP The Swedish teen was followed on her first day in Madrid by a swarm of cameras and reporters, as well as curious members of the public wanting to film her on their smartphones, from the very first step she took out of an overnight train from Lisbon. Two young activists earned cheers as they abseiled from a bridge and strung out a banner saying: "Just 8 years till 1.5 degrees C. HOW DARE YOU?" - a reference to scientists' forecasts of rising temperatures and what activists complain is a lack of a convincing political response to the threat. The crush as people tried to get a glimpse of Thunberg led her to pull out shortly after the start of the march, saying police had advised her to leave for safety's sake, and she climbed into an electric car.

A Madrid police spokeswoman who spoke on condition of anonymity because she wasn't authorised to be named in media reports said that it had only been "suggested" to that Thunberg leave after she appeared "overwhelmed" by the attention and that police never ordered the activist to abandon on safety grounds. Earlier in the day, the 16-year-old had said at a press conference that calls for real action against climate change are still being "ignored" by political leaders despite their continuous praise of the global environmental youth movement she helped create. Thunberg hoped the COP25 summit would lead to "something concrete" and "increasing awareness among people in general," but she said that after more than one year of student strikes"still basically nothing has happened." "The climate crisis is still being ignored by those in power," she added. Consensus proving 'difficult'

During the talks, which run from December 2-13, nearly 200 countries are meant to streamline the rules on global carbon markets and agree on how poor countries should be compensated for destruction largely caused by emissions from rich nations. An official directly involved in the negotiations said that despite a few setbacks, the technical negotiations were progressing, although many issues were being left for ministerial-level meetings in the summit's second and final week. The official, who spoke on condition of anonymity given the sensitivity of the discussions, added that a political declaration on greater "ambition" - a buzzword at the summit - was shaping to be "difficult to achieve." "A summit that doesn't end with enhanced ambition would be something that nobody would understand if we take into account what the streets and science are telling us," the official said. Loading Replay Replay video Play video Play video

The talks came as evidence mounts about disasters that could ensue from further global warming, including a study published Friday predicting that unchecked climate change could devastate fishery industries and coral reef tourism. The study commissioned by 14 nations whose economies rely heavily on the sea says climate change could cause hundreds of billions of dollars in losses by 2050, adding that limiting global warming would lessen the economic impact for coastal countries, but that they also need to adapt to ocean changes. Tipping point for an 'uprising' Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research, said social scientists believed that when roughly 3.5 per cent of a nation's population joins "civil and non-violent uprisings" it can be enough to force change, even in a dictatorship. In Germany, numbers at the climate demonstrations on September 20 were estimated at nearly 2 per cent of the population, and in New Zealand at 3.5 per cent, he said.

"If you start seeing an uprising ... there will be an enormous pressure for the political leadership to step up and start acting," Rockstrom said - though he noted it "can also be quite challenging along the way". Climate activists march in silence during a 'Fridays For Future' protest in Madrid during the COP25 climate talks. Credit:Getty Images He questioned whether, at some point, it would start to become morally unacceptable to cause people's deaths with car exhaust, as happened with cigarette smoking. In New Delhi, at some times of the year, young people are inhaling toxic pollution equivalent to smoking 10 cigarettes a day, killing over 7000 people a year in the city, he noted. On Friday morning, eight-year-old Indian climate striker Licypriya Kangujam, of New Delhi, headed to her country's pavilion at the Madrid talks, clutching a hand-written poster calling on India's Prime Minister Narendra Modi to pass a flagship climate change law in the current parliament session.