As many as 50,000 people are likely to attend the December 2015 talks in Paris aimed at forging a UN pact on climate change, host France said on Tuesday.
"Between 40,000 and 50,000 people from 195 countries are expected," Foreign Minister Laurent Fabius told reporters at the site in Le Bourget, just north of the French capital, where the talks will be held.
Roughly half this number will be official delegates, and the remainder will be support staff or observers, he said.
The talks, under the banner of the UN Framework Convention on Climate Change (UNFCCC), will run from November 30 to December 11, 2015.
The biggest official turnout at climate talks was at the ill-fated 2009 summit in Copenhagen, which drew about 26,600 delegates.
Taking effect from 2020, the Paris agreement must curb heat-trapping carbon emissions that are damaging Earth's fragile climate, amplifying risks from drought, flood, storms and rising seas.
Efforts to secure a deal are intensifying in the run-up to Paris, with a special summit of heads of state and government, called by UN Secretary General Ban Ki-moon, to be held in New York on September 23.
This year's annual round of negotiations in Lima, Peru, in December must yield a draft agreement upon which to build towards Paris.
Countries have committed to announcing their emissions reduction targets by the first quarter of next year.
The United Nations seeks to limit global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Resolution levels, but scientists say current emission trends could hike temperatures to more than twice that level by century's end.
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