More than half a million people from Australia to Paraguay joined the biggest day of climate change activism in history on Sunday, telling world leaders gathering for a summit in Paris there is "No Planet B" in the fight against global warming.

In the French capital, where demonstrations were banned by the authorities after attacks by Islamic State militants killed 130 people on Nov. 13, activists laid out more than 20,000 shoes in the Place de la Republique to symbolize absent marchers on the eve of the summit.

Among the high heels and sandals were a pair of plain black shoes sent by Pope Francis, who has been a vocal advocate for action to prevent dangerous climate change, and jogging shoes from U.N. Secretary-General Ban Ki-moon.