French President Francois Hollande arrived at the venue early on Monday to welcome the leaders which include the UN Secretary General as well as the heads of state of the United States, Russia, China and India among others.
The biggest-ever climate summit, which lasts for 12 days, is aimed at ending two decades of international bickering with a pact that would limit emissions of the greenhouse gases blamed for climate change.
Scientists warn that, unless action is taken soon, mankind will endure ever-worsening catastrophic events, such as droughts that will lead to conflict and rising sea levels that will wipe out low-lying island nations.
Speaking on the occasion, Hollande said that the fate of humanity was at stake in this conference.
“After the attacks in France, we have to deal with the urgent priorities and respond to the terrorist challenge but also act for the long term," he said.
In an interview with French daily newspaper ‘20 minutes’, Hollande said leaders would meet in Paris “to reaffirm their solidarity with France” and to "assume their responsibilities in the face of the warming of the planet”.
“History will judge the heads of state and government harshly if, in December 2015, they miss this opportunity.”
Besides dealing with the climate change, the participating countries have also vowed to forge an ambitious deal to honour the 130 people killed in the November 13 attacks that were claimed by the Islamic State group.
US President Barack Obama's first act after touching down in Paris on Monday was to visit the scene of the worst carnage at the Bataclan concert venue.
The summit is "an opportunity to stand in solidarity with our oldest ally... and reaffirm our commitment to protect our people and our way of life from terrorist threats," Obama said in a Facebook post before flying to Paris.
This is the 21st summit hosted by the United Nations since 1995 to tackle the global warming issue. However, all previous efforts have foundered, primarily due to deep divisions between rich and poor nations.
Many poor nations insist rich countries bear the most responsibility for tackling the problem because they have burnt the most fossil fuels since the Industrial Revolution on their way to prosperity.
But the United States and other developed nations insist more must be done by China, India and other emerging countries, which are burning increasing amounts of coal to power their fast-growing economies.