How much will it cost? Where is it happening? POLITICO takes a look at some of the nuts and bolts of one of the biggest climate summit in history. | ALAIN JOCARD/AFP/Getty COP21 by numbers A look at the biggest-ever climate change conference.

The COP21 climate conference starts Monday under much higher security and in a much darker mood thanks to the Paris terror attacks.

The summit may not quite be the grand show that its French hosts had initially hoped for. However, its primary goal to strike a deal cutting the output of greenhouse gases and limiting the extent of global warming is still in place.

But for a new global agreement to see the light of day, the leaders, ministers, delegates, negotiators, activists, businesses and protestors all need a place to meet. POLITICO takes a look at some of the nuts and bolts of what promises to be the biggest climate summit in history.

40,000 people

There's going to be a crowd. Organizers expect 40,000 attendees, making it the largest so-called Conference of Parties (COP) ever.

Usually, around 10,000 people attend the U.N.’s annual climate conference. The largest previous summit was the Copenhagen COP15 in 2009 with roughly 27,000 participants.

This year's higher numbers are largely due to growing worries about global warming. What used to be the rather esoteric province of scientists and environmentalists has turned into one of the key issues of the age, with everyone from the Pope to oil company executives keen to get involved.

Pierre Cannet of WWF France said COP21 should be considered “not as a show, but as meeting point.” Companies also see “climate change [as] an important topic” and “global threat for our enterprises,” said Christian Thimann, a spokesman for AXA, the financial firm.

So far 150 presidents, prime ministers, as well as a smattering of kings and princes, from Barack Obama to Zimbabwe's Robert Mugabe and the leaders of tiny island nations, are signed up to speak on Monday. There are so many dignitaries that they are divided up between two venues, and each one only gets three minutes. "Time limits will be strictly enforced," say organizers.

After they're gone, bureaucrats and diplomats take over for the next two weeks as they try to hammer out a climate deal by December 11.

€79.5 million for free public transport

The venue is Paris-Le Bourget, right next to an airport about 10 kilometers north of the city center. The organizing committee is encouraging participants to get to the site with public transport. As part of an effort to minimize the conference’s carbon footprint, all accredited participants will be provided with free transport passes for all greater Paris transportation networks for free — at a total cost of €79.5 million.

Since 2005, the COP host country has to promise to minimize the event's environmental impact. Caterers will have to avoid wasting food and supply locally grown and seasonal foods as much as possible. Reduced paper usage, use of recycled paper and recycling are other environmental-friendly measures will be used. Organizers are also looking at energy-efficient ways of heating the venue.

120,000 police and soldiers

Following the deadly attacks on Paris, the French government had to implement unprecedented security measures for the summit, fearing it will be a magnet for terrorists.

France will deploy 2,800 police officers outside the main venues for the COP21, said Interior Minister Bernard Cazeneuve. On top of additional police at Le Bourget, Cazeneuve said that 8,000 officers would bolster security on France’s exterior borders during the conference.

“In total, there will be 120,000 policemen, gendarmes and soldiers that will be deployed throughout the territory,” Cazeneuve said at a press conference.

French forces are not alone. At every Conference of Parties, U.N. security forces ensure the security of the Blue Zone — the negotiation space of the conference only accessible to people in possession of a special U.N., accreditation. So the 10,000 government representatives will be protected by the Blue Helmets.

2,000 protest events in 150 countries

Paris was meant to experience ”the largest mass civil disobedience climate justice action that we have ever seen in Europe,” said Prayal Parekh, a campaigner with the 350.org NGO.

But security concerns after the November 13 attacks prompted authorities to cancel climate marches planned for November 28 and 29, as well as climate protests for December 12.

But activists will still get heard, as events organized for civil society groups at Le Bourget are still on.

With a ban on large street protests, NGOs and activists are coming up with alternative ways to get their point across during the summit. Alternatiba, an NGO, launched an online petition. Coalition Climate 21, representing 130 civil society organizations, plans to cover the Place de la République in Paris with shoes to symbolize all the people who wanted to take part in the marches.

Although climate marches can't take place in the French capital, they will happen in lots of other places. More than 2,000 events are being planned this weekend in more than 150 countries.

Total cost: €187 million

The budget is the biggest ever for a COP, at €187 million. Copenhagen was the runner-up at €142 million.

A report by the French Senate had the following breakdown: €20.5 million for the preparation, €151 million for the organization and €7.5 million for welcoming foreign delegations.

Included in the organizational costs are €64.3 million for the rent, telecoms and security at the venue, and €79.5 million for transportation.

The official reason for the higher costs is the large number of participants, more space for civil society groups and a bigger conference space.

But that cost estimate may be a little optimistic. The event is already €1.2 million in the red.

In addition to the government, businesses are covering about a fifth of the summit cost — something that is outraging many NGOs.

This article was first published on POLITICO Pro.