Addressing international dignitaries at a "Summit of Conscience for the Climate" in the French capital, Hollande called insisted that "an agreement must be found".
As some 40 foreign and environment ministers met elsewhere in the French capital to accelerate flagging UN negotiations, Hollande underlined the urgency -- and difficulty -- of their task.
"Today, with the agreement we see taking shape, we are still above two degrees Celsius, and probably three," he said.
The Summit of Conscience "starts with the fact that the climate crisis, and more broadly the ecological crisis, is not restricted to its scientific, technological, economic and political dimensions".
The United Nations has embraced a goal of limiting average global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels.
Scientists say disastrous climate impacts can be avoided at this threshold, but warn that the world is on course for double the target, or more.
Any global accord reached at the November 30-December 11 talks in Paris will be supported by a roster of voluntary national pledges to cut greenhouse gas emissions over the next 10 to 15 years.
Hollande added that the global economy would have to take a sharp turn towards renewable energy.
Reaching a viable deal, he said, would require "forsaking the use of 80 percent of fossil-based energy resources to which we still have easy access".
Also on Tuesday, 24 of Britain's top academic and professional bodies issued a dire warning of pending climate catastrophe.
For a reasonable chance of staying under 2 C, they said in a joint statement, "we must transition to a zero-carbon world by early in the second half of the century".
A "zero-carbon world" is shorthand for a global economy that, on balance, is not adding any more carbon dioxide into the atmosphere.
The 400-strong "Conscience" gathering of religious and mo