It promises to be an unparalleled demonstration of the world’s fury at its leaders’ continued failure to tackle climate change: an unprecedented statement by hundreds of thousands of people.

Today, and for the next two days, before a key meeting on climate change at the UN in New York, protesters will take to the streets, from Papua New Guinea to central London.

Campaigners say the cost of climate change – estimated at 650 million people affected, 112,000 lives lost, hundreds of billions of pounds in the past five years alone – must produce real commitments from world leaders.

Before Tuesday’s summit, when the UK Government will sign up to a new reforestation commitment, 2,000 rallies and protests are planned across 150 countries.

In London, thousands are expected at the People’s Climate March this lunchtime, walking from Victoria Embankment Gardens to Parliament Square, including Emma Thompson, Peter Gabriel and Vivienne Westwood. Meanwhile, in New York, organisers are anticipating more than 100,000 people. In a highly unusual campaigning appearance, the UN Secretary General, Ban Ki-moon, will be among them, as will Lionel Messi, Brian Eno, Susan Sarandon, William Shatner and Kiefer Sutherland.

In rural Papua New Guinea, primary school students will march to a nearby lighthouse which is becoming submerged as sea levels rise.