The stream of world leaders continues into the Le Bourget conference centre. 

Here's some of what we can expect at COP21 today:

• 10:00 Paris time (09:00 GMT) - opening ceremony, which sees the French government formally take over the running of the talks
• 12:00 CET (11:00 GMT) - a first batch of three-minute speeches from the country leaders present will ensue in two consecutive sessions
• Presidents Barack Obama (US), Xi Jinping (China) and Vladimir Putin (Russia) are all part of that first session
• 14:45 CET (13:45 GMT) - a second batch of speeches will include British prime minister David Cameron and Germany's Angela Merkel, among many others

Image source, Reuters

Roger Harrabin
BBC environment analyst

The biggest change between the failed Copenhagen climate summit and the relative optimism of Paris is not politics but technology, says Michael Jacobs, who advised the UK government in Copenhagen.

In my documentary on BBC Radio 4 this evening at 8pm, he tells me the other big factors are Obama's hunt for a legacy and China's realisation that coal is killing its people.

All three episodes of Changing Climate will be on BBC iPlayer and full interviews are collated on the Open University website creativeclimate.org, external

The Indian prime minister Narendra Modi, in an opinion piece in the Financial Times, struck a note of caution about the talks.

He said there were still huge differences between the developing and developed world and the richer countries simply had to take more of the burden in dealing with climate change.

Francois Hollande could not be accused of underestimating the importance of the COP21. In an interview with France's 20 Minutes newspaper, he said:

Image source, EPA

President Obama landed in Paris on Sunday evening ahead of the conference and went straight to the Bataclan concert hall, where 89 people were killed in the terror attacks a little over a fortnight ago.

Obama was accompanied by French president Francois Hollande and Paris mayor Anne Hidalgo.

Obama is due to speak at the climate summit today among 140 heads of state.

Each has been given three minutes and there will be two parallel sessions, commencing at 11:00 GMT.

Good morning and welcome to our live coverage of the Paris climate summit's first full day. The day is due to kick off with an opening ceremony at 09:00 GMT.

We'll start today with some insights from our team - including environment correspondent Matt McGrath who faced an early start amid justifiably tight security...

Yesterday evening, science correspondent Rebecca Morelle was investigating the facilities:

And in London yesterday, environment correspondent Claire Marshall got a birds-eye view of the climate march:

That's it from our team in Paris for today; we'll be back at 08:00 GMT tomorrow.

We'll leave you with a photo of the Eiffel Tower, lit up this evening in support of climate action.

Image source, Reuters

Rally organisers Avaaz say more than 570,000 people participated in climate marchers worldwide today, according to their early estimates.

The group's campaign director Emma Ruby-Sachs described the call from the public as "deafening".

"Despite events being cancelled across France, global actions were larger than last year's massive march in New York, breaking records in Bangladesh, Australia, Britain and more," she said.

Image source, AP

Image source, AFP

Image source, EPA

The French president Francois Hollande, speaking at an EU-Turkey summit in Brussels, said the violence in Paris had been caused by troublemakers.

The AFP wire agency is reporting that candles from a memorial to victims of the recent terror attacks in Paris were thrown at police during the disturbances that followed a climate demonstration.

People took to social media to express their disgust. 

UN Executive Secretary Christiana Figueres has tweeted from the opening session of the ADP negotiations, the most important part of COP21.

The Adhoc Durban Platform on enhanced action (ADP) is the programme of negotiations that began in South Africa in 2011 and is due to end in a new global deal here in Paris.

The session was brought forward to Sunday, preceding Monday's opening ceremony, with the UN saying that "an early opening of the session will offer an opportunity to make the best possible use of the very limited time available to finalise negotiations".

The organisers of the London climate march say more than 50,000 people joined in their event.

Alex Wilks, campaign director at Avaaz, called it "the biggest climate march in British history".

Image source, AFP

Matt McGrath
Environment correspondent, BBC News

A minute's silence was observed at a negotiating session this afternoon here at Le Bourget, in memory of the victims of the recent terror attacks.  

Negotiators at COP21, conscious of the short amount of time they have at this meeting to craft a deal, have decided to start work early.

"The best way to honour the memory of those who have fallen, those who are victims of barbaric attacks, is to carry out what we have committed to," said the co-chair of these talks, Ahmed Djoghlaf.

Meanwhile in London, Emma Thompson is among the marchers.

Image source, EPA

Christian Aid's Joe Ware was in the Place de la Republique when the scuffles broke out. He told BBC News that in his view the police were well prepared for trouble. 

"There were hundreds and hundreds of riot police and I saw at least 20 riot vans in the areas around the square. 

"As I was leaving there was tear gas being fired; I was with other people who had been in tear gas situations before and they assured me that's what it was."

Image source, Hawkey

According to the AFP news agency, the masked protesters were shouting "State of emergency, police state" - referring to the emergency restrictions introduced after the November 13th terror attacks.

Paris police chief Michel Cadot told AFP that about 100 people had been detained after the demonstration turned violent. He said that police identified about 200 or 300 people who violated a ban on all protests under the country's state of emergency.

The state of emergency was declared in the wake of the recent extremist attacks in Paris.

Cadot said the 100 people who were detained were found to have projectiles or other suspicious objects.

Image source, REUTERS

One of the groups who organised the climate events in Paris has condemned the scuffles at the Place de la Republique and moved to distance itself from the troublemakers:

The AFP news agency reports that 100 people have been detained following the clashes that took place after a climate demonstration near the Place de la Republique in Paris.