A farmer burns a paddy field in Thailand's Phitsanuloke province, about 377 km (234 miles) north of Bangkok, March 29, 2008. A new U.N. treaty to fight climate change should aim to halve greenhouse gas emissions by 2050, the U.N.'s top climate change official said on Friday.Senior officials from up to 190 nations will meet from March 31-April 4 in Bangkok for the opening session of two years of meetings to work out a new global warming pact to widen and succeed the United Nations' Kyoto Protocol. REUTERS/Chaiwat Subprasom (THAILAND)