U.S. President Barack Obama warned Tuesday global warming posed imminent security and economic risks, as negotiators embarked on an 11-day race to seal a U.N. pact aimed at taming climate change.

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

Weather-related disasters in the past two decades have killed more than 600,000 people and inflicted economic losses estimated at trillions of dollars, the United Nations said on Monday, warning that the frequency and impact of such events was set to rise.

The figures were released before a United Nations-backed climate meeting, starting next Monday in Paris, at which more than 120 national leaders will try to rein in greenhouse gas emissions and slow the rise in global temperatures.

Luka Kinyere felt the wet, dark volcanic soil in his calloused palm, thankful for the rain that was falling again after a dry spell.

Although the coffee plants in his plantation were turning green, dry conditions had doomed his chances of turning a profit from this year's second harvest.

Despite the organization and funding behind groups which try to cast doubt about the causes and implications of climate change, the facts have spoken. The world continues to warm and their favorite myths have died.

We know that human-emitted heat-trapping gases warm the planet. In fact, this has been known for well over a century. With modern instruments (like ocean thermometers and satellites among others) we are now measuring the change. With advanced climate models, we can predict the changes. The measurements and the predictions are in excellent agreement, despite what cable news and second-rate skeptical scientists say.

Northern China choked under some of the worst smog this year on Monday, with Beijing's pollution soaring to 22 times healthy limits, triggering the city's second-highest air alert on the eve of global climate change talks.

Thick haze blanketed cities across the country after President Xi Jinping arrived in Paris for the talks where China, the world's largest emitter of greenhouse gases, will be central to discussions.

World leaders opened an historic summit in the French capital on Monday with "the hope of all of humanity" laid on their shoulders as they sought a deal to avert a climate catastrophe.

The heads of more than 150 nations kicked off 12 days of talks in search of an elusive pact that would indirectly restructure the world economy, weaning it off fossil fuels that stoke global warming.

Climate negotiators in Paris vowed Sunday to craft an historic pact to avert catastrophic global warming in honor of the victims of this month's horror attacks in the French capital.

The undertaking was made as negotiators met ahead of Monday's formal opening of a two-week conference tasked with forging a pact unifying long-bickering nations in the struggle to end the world's dependence on climate-altering fossil fuels.

Protesters linked hands near the violent heart of the Paris terror attacks Sunday, giving an emotional jolt to world leaders flying into the French capital to try to save Earth from a climate catastrophe.

As hundreds of thousands of people joined worldwide protests, the human chain aimed to send a highly symbolic message to leaders on the eve of the official opening of a 195-nation UN climate summit in Paris.

The campaign to sell off investments in fossil fuel projects, particularly those involving coal, is no longer a fringe movement as big players like banks and investment funds get on board.

The divestment campaign has come a long way from its beginnings in the United States, where students began pressuring their university investment funds in 2008 to pull their money out of companies connected with fossil fuels.

Thousands turned out for climate change marches in Manila and Brisbane Saturday, part of a weekend of action across the globe to demand results from next week's historic Paris summit.

Religious clergy, students and activists marched through the Philippine capital calling for curbs on emissions to mute the impact of climate change, which is blamed for a spike in typhoons and extreme weather that has wreaked havoc on the nation.