Reuters: The world should widen a fight against global warming by curbing a string of pollutants other than carbon dioxide, the main greenhouse gas, the U.N. Environment Programme (UNEP) said on Friday. Heat-trapping methane, nitrogen compounds, low-level ozone and soot are responsible for almost half of the man-made emissions stoking climate change in the 21st century, it said. A wider assault on pollutants, twinned with cuts in carbon dioxide, would help toward a new U.N. climate pact …