US President Barack Obama has warned global warming poses imminent security and economic risks, as negotiators embarked on an 11-day race to seal a UN pact aimed at taming climate change.

But, speaking on Tuesday after attending an historic climate summit with 150 other leaders, Obama voiced confidence mankind would make the tough decisions to brake rising temperatures.

Obama and others employed lofty rhetoric on Monday to inject energy into the start of the UN negotiations, which are due to deliver a global masterplan on December 11.

The president followed that up on Tuesday with grim warnings for the near future if the temperature curve went unchecked.

"Before long we are going to have to devote more and more of our economic and military resources, not to growing opportunity for our people, but to adapting to the various consequences of a changing planet," Obama said.

"This is an economic and security imperative that we have to tackle now."

The talks in Paris aim at an accord which, taking effect from 2020, would slash carbon emissions - the emissions that come mainly from burning fossil fuels - and deliver hundreds of billions of dollars in aid for climate-vulnerable countries.

But it is only the latest chapter in a 25-year-old diplomatic saga marked by spats over burden-sharing and hobbled by a negotiation system of huge complexity.

Behind their vows of support, many leaders have often preferred the short-term benefits of burning cheap and dependable fossil fuels to power prosperity, ignoring the consequences of carbon pollution.

Despite this, Obama said he believed the global political landscape was shifting, boding well for Paris and beyond.

"Climate change is a massive problem, it is a generational problem. And yet despite all that, the main message I have got is, I actually think we are going to solve this thing," Obama said.

At the heavily secured summit venue in Le Bourget on the northern outskirts of Paris, a city on edge since the November 13 terror attacks that killed 130 people, bureaucrats from 195 nations began a frantic effort to distil a 54-page text into a global warming blueprint.

They have until just Saturday to iron out as many differences as they can, before handing the text over to environment and foreign ministers and a final push for a pact.