It may seem like a small number, but it's central to the 12-day conference. The goal of COP21 is to reach a global agreement to cap warming at 2C (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels. If emissions keep rising at the current rate, we will instead see a rise of 5C - which, coincidentally, was the same change in temperature between the last Ice Age and today.
The number of people hired to work at COP21. Although organizers had promised local workers would get "priority treatment" for jobs generated by the summit, at least 200 of these workers were revealed to have been subcontracted from eastern Europe, reportedly on low paid contracts.
The amount one Slovakian worker was paid for a 12-hour shift, according to France TV. The man was allegedly hired by GL events to work on COP21 preparations, however this salary would be illegal as it is below France's minimum wage, which would see him earning at least €115 for 12 hours' work.
The number of police France's interior minister announced would be deployed, of which 2,800 will be stationed at the conference venue, with the remaining 8,000 carrying out border checks. France had planned to introduce border checks during the climate summit, but security measures are being ramped up as the event comes just over two weeks after the deadly terror attacks on the city.
The number of truly legally binding and global treaties on climate change before now. The Kyoto protocol commits only developed nations to a reduction in greenhouse gases while eight days of talks in Copenhagen in 2009 ended with an agreement which "recognized" the need to cap temperature rises but did not contain any commitments to do so. It is hoped that the Paris summit will be more successful.
The number of world leaders who will be in attendance. Notable presences include long-time climate change sceptic Vladimir Putin, US President Barack Obama, Indian Prime Minister Narenda Modi and China's President Xi Jinping.
Photo: Alain Jocard/AFP
The total number of participants. This figure includes 25,000 official delegates (government figures along with representatives from intergovernmental organizations, UN agencies, NGOs, civil society), 3,000 accredited journalists who will be noting down every development, organizers, speakers and world leaders.
The total budget, in euros, to be spent on COP21. The gathering is expected to generate €100 million of income for the Ile de France regions.
The proportion of biodiversity which could be lost before the end of the century if global warming continues at current rates.
The increase in Airbnb reservations in Seine-Saint-Denis, near to Bourget, for the duration of the conference. Local hotels haven't seen the boom in reservations they were hoping for, and are pointing the finger at the home-sharing service for taking their custom.
That's how much CO2 is expected to be produced just by hotels during the conference, not taking into account the emissions from transport, electricity and other sources linked to COP21. To compensate, organizers plan to have 27,000 trees planted in Peru.
This is the carbon footprint of a large cappuccino, measured in grammes of CO2 equivalent (gCO2e). A large proportion of the emissions come from raising the cow to produce the milk. For a cup of home-made tea or coffee with no milk, the figure is just 21 gCO2e. As well as getting world leaders to agree on limits for carbon emissions, the conference also aims at making ordinary people more aware of their contribution to climate change.