Some 150 heads of state and government, including US president Barack Obama and Chinese counterpart Xi Jinping, urged each other to agree in two weeks of talks to steer the world away from fossil fuels.
They arrived at UN climate change talks in Paris with high expectations and armed with promises to act. After decades of struggling negotiations and the failure of a summit in Copenhagen six years ago, some form of landmark agreement appears all but assured by mid-December.
Warnings from climate scientists, demands from activists and exhortations from religious leaders such as Pope Francis have coupled with major advances in cleaner energy sources like solar power to raise pressure for cuts in carbon emissions.
Most scientists say failure to agree on strong measures in Paris would doom the world to ever-hotter temperatures, bringing with them deadlier storms, more frequent droughts, and rising sea levels as the polar ice melts. Facing such projections, the leaders of nations responsible for about 90% of the world’s greenhouse gas emissions have come bearing pledges to reduce their carbon output.
Over the next two weeks, negotiators will hammer out the strongest international climate pact yet.
“What should give us hope that this is a turning point, that this is the moment we finally determined we would save our planet, is the fact that our nations share a sense of urgency about this challenge and a growing realisation that it is within our power to do something about it,” said Mr Obama.
Security has been tightened after Islamist militant attacks killed 130 people on November 13, and Mr Hollande said he could not separate “the fight with terrorism from the fight against global warming”.
Leaders must face both challenges, leaving their children “a world freed of terror” as well as one “protected from catastrophes”.
On the eve of the summit, an estimated 785,000 people from Australia to Paraguay joined the biggest day of climate change activism in history, telling world leaders there was “no Planet B” in the global warming fight. The US and China “have both determined that it is our responsibility to take action”, Obama said after meeting Mr Xi.
That partnership has been a balm for the main source of tension that characterised previous talks, in which the developing world argued that countries that grew rich by industrialising on fossil fuels should pay the cost of shifting all economies to a renewable energy future.
Now even China, once a leading voice of that club, has agreed to contribute to a Green Climate Fund that hopes to dispense €94.5bn a year after 2020 as a way to finance the developing world’s shift towards renewables.