Agence France-Presse: China has leapfrogged the United States as the world’s biggest carbon emitter and India is heading for third place, scientists said on Friday in a report that warned global greenhouse-gas levels were scaling record peaks. The report, by a research consortium called the Global Carbon Project (GCP), confirms an estimate that China has become the biggest producer of carbon dioxide (CO2), the principal gas that causes global warming. Until 2005, rich countries emitted most of the world’s …