Tough, unresolved issues keep the United States, European Union, Canada, Japan and Australia far apart from developing nations, a month before an "Earth Summit" formally called the World Summit on Sustainable Development (WSSD), that will bring some 100 world leaders and 60,000 participants to Johannesburg. South Africa's foreign Minister Nkosazanna Dlamini-Zuma will chair an "informal" New York meeting of representatives from 25 countries in an effort to bridge the gap of differences.