Bill Clinton and New York Mayor Michael Bloomberg have decided to merge their global climate groups. The new group will be a combination of C40, the Bloomberg-run coalition of international cities, and the Clinton Climate Initiative, one of Clinton’s philanthropic projects. Both groups seek to cut carbon emissions in major cities by reducing energy use in buildings, promoting mass transit, and reusing greenhouse gases emitted from landfills. Cities account for 70 percent of carbon production. The combined group will likely have a budget of $15 million and a staff of 70, with main offices in New York, Los Angeles, and London.