WATCH: World leaders gather for crucial climate change talks

World leaders have gathered for a critical climate conference in Le Bourget, outside Paris, today.

UN Secretary General Ban Ki-moon declared the moment of silence in honour of people killed in recent attacks in Paris, Beirut, Baghdad, Tunisia and Mali as he launched two weeks of talks in Paris aimed at a long-term deal to slow man-made global warming.

Organisers sought a high-level kick-off to the talks in hopes of providing impetus for a strong agreement. They say 151 world leaders are expected to attend.

Some leaders have visited the sites of the deadly November 13 attacks in Paris. US president Barack Obama laid a flower at a concert hall where dozens of people were killed.

Peruvian Environment Minister Manuel Pulgar Vidal, who played host to the last UN climate conference in Lima, declared this year's meeting open.

Mr Vidal said a deal would show the world that countries can work together to fight global warming as well as terrorism. The talks are occurring just two weeks after deadly attacks in Paris by so-called 'Islamic State' extremists.

Leaders are set to pledge billions of pounds to research and develop a technical fix to the planet's climate woes.

Clean energy technology is being promoted as the key to fighting global warming at the UN climate summit.

UN Secretary General Ban Ki-moon, French president Francois Hollande, the head of the UN climate change agency Christina Figueres, and French Environment Minister Segolene Royal, greeted heads of state and government from around the world as they arrived at the conference centre near the Le Bourget airfield just north of Paris.

Afterwards, each leader will give a speech laying out their countries' efforts to reduce man-made emissions and cope with climate change.

Microsoft founder Bill Gates, US president Barack Obama and Mr Hollande will launch a joint initiative after a diplomatic push in recent weeks ahead of the Paris climate conference.

A key goal is to bring down the cost of cleaner energy. At least 19 governments and 28 leading world investors, including Facebook founder Mark Zuckerberg, billionaires George Soros and Saudi Prince Alaweed bin Talal, and Jack Ma of China's Alibaba, have signed on so far.

"It's quite a big deal," said Jennifer Morgan, global climate director for the World Resources Institute.

"It brings a new kind of burst of energy into the conference right at the beginning on something very important."

The UN summit formally opened on Sunday afternoon with a minute of silence for the victims of this month's Paris attacks and vows not to let terrorism derail efforts to slow or stop climate change.

But a few miles away, police trying to secure the nation against new violence sprayed tear gas on protesters who defied a ban on demonstrations and threw projectiles.

Mr Hollande is urging a strong, binding global agreement to fight climate change.

Mr Hollande told other world leaders gathered that a solid global warming deal would help ensure world peace for future generations and reduce the number of refugees fleeing increasingly extreme weather.

He linked the fight against global warming to the fight against extremism.

"What is at stake with this climate conference is peace," he said.

"The fight against terrorism and the fight against climate change are two major global challenges we must face."

He called for a "deep change" in human attitudes toward resources and the planet.