French President Francois Hollande, left, French Foreign Affairs Minister Laurent Fabius and United Nations Secretary General Ban Ki-moon, right, attend a plenary session of the COP21.

World leaders have launched an ambitious attempt to hold back rising temperatures, with the United States and China leading calls for the climate summit in Paris to mark a decisive turn in the fight against global warming.

In a series of opening addresses to the U.N. talks, heads of state and government exhorted each other to find common cause in two weeks of bargaining to steer the global economy away from its dependence on fossil fuels.

French President Francois Hollande said the world was at a “breaking point”.

The leaders arrived 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 agreement – likely to be the strongest global climate pact yet – appears all but assured by mid-December.

“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 realization that it is within our power to do something about it,” said U.S. President Barack Obama, one of the first leaders to speak at the summit.

The leaders gathered in a vast conference center at Le Bourget airfield. In all, 195 countries are part of the unwieldy negotiating process, with a variety of leadership styles and ideologies that has made consensus elusive in the past.

Key issues, notably how to divide the global bill to pay for a shift to renewable energy, are still contentious.

“Climate justice demands that the little carbon space we still have, developing countries should have enough room to grow,” said India’s Prime Minister Narendra Modi, a key player because of his country’s size and its heavy dependence on coal.

One difference this time may be the partnership between the United States and China, the two biggest carbon emitters, who between them account for almost 40 percent of the world’s greenhouse gas emissions, according to the World Resources Institute think-tank.

Related articles across the web

• PM Narendra Modi arrives in New York on second US visit
• PM Modi arrives in New York for his five-day US visit
• No bilateral meeting scheduled between Modi, Sharif in U.S.
• Pak PM Sharif likely to raise Kashmir issue at UN meet
• India To Concentrate On Critical Issues At UNGA Session
• Summit Charts New Era of Sustainable Development
• Indian PM in US to attend UNGA, woo investors
• Modi arrives in US; packed schedule ahead of him
• Kofi Annan: UN security council must expand and reform - video interview
• Modi in Silicon Valley