World leaders including UN Secretary-General Ban Ki-moon were set to join farmers, fishermen, children, and others in a massive demonstration on Sunday to demand action on climate change.
Organizers are expecting 100,000 to join the People's Climate March in midtown Manhattan ahead of this week's U.N. General Assembly, which brings together 120 world leaders to discuss reducing carbon emissions that threaten the environment.
The New York rally was expected to be the largest on a day of events in 161 countries including the United Kingdom, France, Afghanistan, and Bulgaria.
The gathering will include celebrities such as musician Sting, scientists in lab coats, labor groups, 20 marching bands, and floats powered by biodiesel vehicles or pulled by hand, said Jamie Henn, spokesman for 350.org, which organized the event with more than a dozen other environmental, labor, and social justice groups.
"You can't fight climate change sitting on your couch and holding your breath," Henn said.
Organizers said the massive mobilization is aimed at transforming climate change "from an environmental concern to an everybody issue.'"
The United Nations on Tuesday is set to host a climate summit where world leaders will continue talks toward a pact 200 nations are working on that would rein in the rising greenhouse gas emissions. Negotiators aim to complete that deal in late 2015.
In London, actress Emma Thompson and fashion designer Vivienne Westwood were among celebrities who took part in a march of thousands of people who processed through central London towards a rally by parliament.
"Politicians are not showing the will. There is not a problem with the science, there is a problem with the political will," said Ben Phillips, campaigns director for Oxfam. "That is why it is so important that people are marching here today."
New York City Mayor Bill de Blasio, who is expected to join the marchers, on Sunday unveiled a new plan for the city to reduce its greenhouse gas emissions by 80 percent from 2005 levels by 2050.
All 3,000 city-owned buildings that use significant amounts of energy would be retrofitted with energy saving heating, cooling and light systems by then, he said, though meeting the commitment will also require significant investments by private landlords.
"Climate change is an existential threat to New Yorkers and our planet. Acting now is nothing short of a moral imperative," de Blasio said.
The 2-mile (3.2-km) route sanctioned by the New York Police Department winds pastTimes Square, where dozens of giant billboards flash even at midday and attempts at eco-friendly signs - lit by wind power - have been spotty.
Organizers bill the event as the largest gathering focused on climate change since 2009, when tens of thousands of people gathered in Copenhagen in a sometime raucous demonstration that resulted in the detention of 2,000 protesters.
“Own a trumpet? Bring it. Own a vuvuzela? Definitely bring it,” said Bill McKibben, co-founder of 350.org, a Brooklyn-based activist organization against climate change, which helped organize the march. “Whistles, drums, tin cans, vocal cords – we're going to make a noise that will echo down over the eons.”