In a year of mounting deaths and economic destruction from record-breaking floods, wildfires and drought, protesters have planned more than 500 gatherings in 54 countries - from Pakistan and Nigeria to the United States.
Organizers of the protests expect global turnout over the weekend to total more than a million people. That could make this weekend's action the largest international climate protest since before the Covid-19 pandemic when the "school strike" movement led by Swedish activist Greta Thunberg saw millions of people worldwide join marches.
"This is directed at world leaders," said Mitzi Jonelle Tan, a climate activist with youth movement Fridays for Future in Manila, the Philippines.
"The fossil fuel industry's time is up. We need a just transition, and we need to phase out the fossil fuels causing the destruction of our environment," she told Reuters.
Organizers said they would call on governments to immediately end subsidies for oil and gas and to cancel any plans for expanding production.
Governments spent a record-high $7 trillion in subsidies to oil, gas, and coal last year, according to an IMF analysis.
"We're taking to the streets to demand that African leaders phase out fossil fuels and focus on investing in community-led renewable energy, to meet the energy demand for the 600 million Africans who do not have access to electricity," said Eric Njuguna, a climate activist based in Nairobi, Kenya.
The demonstrations take place two months before this year's U.N. COP28 climate summit, where more than 80 countries plan to push for a global agreement to gradually phase out coal, oil, and gas.
The burning of fossil fuels is the main cause of climate change, but countries have never agreed in U.N. climate talks to phase out fossil fuels - though they have committed to phase down the use of coal power.
Governments reliant on oil and gas revenues, and those planning to use fossil fuel-based energy to improve poor communities' living standards, are expected to push back on the proposal.
Wealthy nations will also face pressure to offer far more funding to help developing countries invest in low-carbon energy.
Renewable energy is cheaper than fossil fuels in terms of its running costs, but communities need support to make the upfront investments required to quickly build wind farms and install solar panels.
Despite having plentiful solar energy resources, Africa received only 2% of global investments in renewable energy over the last two decades, the International Renewable Energy Agency has said.
Around 15,000 people were expected to join a march in New York on Sunday, as leaders gather for next week's U.N. General Assembly, as well as a "climate ambition summit" on Wednesday. U.N. Secretary-General Antonio Guterres is expected to ask governments to strengthen their plans for cutting planet-warming emissions.
A U.N. report last week warned that the world was on a dangerous track toward severe global warming, and said more action was needed on all fronts, including a drastic drop in coal-fuelled power use by 2030.
The report also urged a massive boost in financial investment to developing countries for both clean energy and measures to adapt to rising heat, worsening storms, and other consequences of the warming climate, the U.N. said.