Germany ? A tax on airline tickets and an auction of pollution rights are just two ideas likely to be studied at a 162-nation conference examining ways of raising the billions of dollars needed every year to fight global warming.

More than 2,000 delegates opened the two-week meeting Monday, launching an 18-month process of intense negotiations on an agreement to succeed the Kyoto Protocol, which expires in 2012.

Discussions began with a warning from poor countries and environmentalists that global warming already is harming millions of people, worsening the global food crisis and changing Earth more rapidly than scientists earlier predicted.

The Bonn talks are to go into the details of an agreement to be concluded in December 2009 and signed in Copenhagen, Denmark. The talks are based on an accord reached in Bali last December when the United States, India and China indicated they would take part in a post-2012 arrangement.