French President Francois Hollande will speak to the group in Lyon on Wednesday -- the hottest day of the year so far in parts of France.

The meeting is part of France's strategy to get as many people implicated in climate negotiations as possible, to increase the pressure on world leaders to reach a global accord to reduce emissions.

French development minister Anick Girardin told the gathering that it's often easier for municipal leaders to prevent climate disasters and clean up towns than it is for governments worldwide to agree on emissions targets.