People’s Climate March in New York and cities worldwide hopes to put pressure on heads of state at Ban Ki-moon summit

Hundreds of thousands of people are expected to take to the streets of New York, London and eight other cities worldwide in a fortnight to pressure world leaders to take action on global warming, in what organisers claim will be the biggest climate march in history.

On 23 September, heads of state will join a New York summit on climate change organised by Ban Ki-moon, the first time world leaders have come together on the issue since the landmark Copenhagen summit in 2009, which was seen as a failure.

The UN secretary general hopes the meeting will inject momentum into efforts to reach a global deal on cutting greenhouse gas emissions by the end of 2015, at a conference in Paris.

Ricken Patel, executive director of digital campaign group Avaaz, one of the organisers of the People’s Climate March on 21 September, said the demonstration was intended to send a signal to those world leaders, who are expected to include David Cameron and Barack Obama, though not heads of state from China and India.

“We in the movement, activists, have failed up until this point to put up a banner and say if you care about this, now is the time, here is the place, let’s come together, to show politicians the political power that is out there on there. Our goal is to mobilise the largest climate change mobilisation in history and the indications are we’re going to get there,” he told the Guardian.

Patel said he expects more than a hundred thousand people at the New York march alone, which will be the focus of the day’s events. Although many of the hundreds of organisations that have committed to taking part are environmental groups, he said not all those attending would be traditional ‘green’ activists.

“There’s a very strong range and diversity of people from all walks of life, including immigrant rights groups, social justice groups. Whoever you are and wherever you are, climate change threatens us all so it brings us together.”

Open contributions: Climate March

Nearly 400,000 have signed a call on Avaaz’s site, saying they will attend one of the global events, which also include marches in Berlin, Paris, Delhi, Rio and Melbourne.

Patel added: “We’re building for the longterm here. This is about launching a movement that can literally save the world over the longterm. We want to build to last. We recognise that at this stage what needs be done is build political momentum behind this issue – our governments are nowhere near even the planning to reach the agreements needed to keep warming below [temperature rises of] 2C.”

Around 500 adverts will appear on the London tube network from Monday, calling on people to join the march, and advertising has already appeared across the New York subway. In Rio, the organisers have permission to project messages about the march on to the statue of Christ.

Facebook Twitter Pinterest Thousands of people had taken part in the 2009 climate march in London. Photograph: Janine Wiedel/Alamy

In an open letter to be published this week, environment and development groups including Greenpeace, Oxfam and WWF, plus politicians including Green party MP Caroline Lucas and Labour MP Tom Watson, have joined with trade unions and faith groups to call on world leaders to use the UN summit to take action on climate change.

“Politicians all over the world cite a lack of public support as a reason not to take bold action against climate change. So on 21 September we will meet this moment with unprecedented public mobilisations in cities around the world, including thousands of people on the streets of London.

“Our goal is simple – to demonstrate the groundswell of demand that exists for ambitious climate action,” they write.

Celebrities backing the People’s Climate March include model Helena Christensen, musician Peter Gabriel, actor Susan Sarandon, Argentine footballer Lionel Messi and actor Edward Norton.

The previous biggest assembly for a climate march was in Copenhagen in 2009, when tens of thousands of people took to the streets.

Separately on Monday, NGOs Greenpeace, WWF, Green Alliance, RSPB and Christian Aid published a report, Paris 2015: Getting a global agreement on climate change, laying out the level of ambition required for a deal at the UN climate talks in Paris.

Matthew Spencer, Green Alliance’s director, said: “There is a fashionable pessimism about multilateralism which shields people from disappointment but does nothing to protect us from the insecurity that climate change is bringing. Only a strong international agreement can avoid that and give nation states the confidence that they will not be alone as they decarbonise their energy systems.”