#PeoplesClimate trending on Twitter as over 10,000 people are expected to take part in The People's Climate March in London.
The march and rally is aimed at demanding urgent action on climate change.
Around the world, other mass demonstrations took place including New York, Berlin, Rio, Lagos and Melbourne. There are over 2,000 events in 150 countries ahead of a UN climate summit next week.
The UN summit is headed up by Secretary General Ban Ki-moon to mobilise debate and discussion before the conference in Paris next year, where it is hoped that a new global climate treaty can be agreed.
Ahead of the London rally, actress Emma Thompson told the Daily Mail: "Every single person on this Earth has the power to change the world. And when we all come together, our power becomes irresistible.
"Together we have built countries and cultures and technologies. Now we must use our power to tackle the biggest threat humanity has ever faced."
The Climate Summit will take place on 23 September 2014 at UN Headquarters in New York. It is being attended by more than 120 world leaders, including Prime Minister David Cameron. The summit will look at reducing the world temperature by two degrees Celsius in 2015.
Friends of the Earth's head of campaigns, Andrew Pendleton said: "Time is running out to avoid catastrophic climate change – international talks are not enough, we need urgent action too.
"The developed world, which is chiefly responsible for the crisis we face, must take the lead by cutting its emissions furthest and fastest.
He added: "The UK's environmental credibility has been sinking for years. The government has been bending over backwards to develop fracking and extract more dirty gas and oil, instead of investing in the UK's huge renewable power potential and a cleaner future for us all."
— David Stazicker (@DavidStazicker) September 21, 2014