French president Francois Hollande has met environmental groups, pushing for an ambitious global deal to reduce man-made emissions blamed for global warming.
The talks, which had an emphasis on helping developing countries adapt to a changing world, in the Elysee Palace came as world leaders prepare to converge on Paris to launch two weeks of high-stakes talks.
Leaders and climate negotiators from 196 countries meeting at the UN talks from November 30-December 11 will try to hash out the broadest, most lasting deal to date to slow global warming.
Saturday's meeting and the talks are taking place under extra-high security after Islamic extremists killed 130 people in Paris on November 13.
Security was already planned to be tight even before the attacks, given the throng of government leaders attending.
French interior minister Bernard Cazeneuve said on Saturday that just under a thousand people thought to pose security risks have been banned from entering the country since tighter border controls were enforced earlier this month in the run-up to the COP21 climate talks and in the wake of France's deadliest attacks in recent memory.
Later foreign minister Laurent Fabius symbolically handed over the "keys" to the climate conference to the UN climate change agency, which will oversee the two-week talks.
Mr Fabius and Mr Hollande have travelled the world this year and used France's diplomatic weight to try to rally international support for a tough and binding deal.
"The keys to the (conference) are now in the hands of the UN, a symbolic key of hope," Mr Fabius tweeted after handing over a giant key to Christiana Figueres, head of the UN Framework Convention on Climate Change.
Ms Figueres, speaking at a joint news conference, evoked a moral, economic and technological imperative "to act now on climate change".
"On the 11 of December (when the conference closes) I want to be able to pronounce six simple words that will be the outcome of unprecedented efforts," Mr Fabius said: "The Paris agreement has been approved."
The last global climate treaty, the 1997 Kyoto Protocol, required only rich countries to reduce emissions and the US, the world's biggest emitter, did not take part.
The changing of the guard for the climate conference means that UN security now takes over the watch inside the vast conference site outside Paris, while 2,800 French forces guard surrounding zones during the two-week conference.
The talks are happening with France in a state of emergency and thousands of troops and police fanned out to ensure security after the Paris attacks.
A big march by environmental activists was cancelled because of the security measures. Activists are still planning other small actions around France and other countries.
Greenpeace anchored a hot air balloon next to the Eiffel Tower on Saturday bearing the words "rise up for renewables".