At the heart of the discord is how to divide the burden of cutting emissions of heat-trapping gases, including carbon dioxide.Such emissions, primarily from the burning of fossil fuels such as coal and oil, have increased by 20 percent since 2000, according to a U.N. report released last week.Van Ypersele (vahn EE-purr-say-luh) said the slow pace of the talks was frustrating and that negotiators